Keeping these around has two problems:
1) Each desc takes 64 bytes, 10 of them is 640B. This is a lot of
overhead on a 1024 byte chunk.
2) It can take well over a week to reach a point where this and thus
Prometheus memory usage as a whole enters steady state. This makes RAM
estimation very hard for users, and makes it difficult to investigate
things like memory fragmentation.
Instead we'll wipe them during each memory series maintenance cycle, and
if a query pulls them in they'll hang around as cache until the next
cycle.
Two cases:
- An unarchived metric must have at least one chunk desc loaded upon
unarchival. Otherwise, the file is gone or has size 0, which is an
inconsistency (because the series is still indexed in the archive
index). Hence, quarantining is triggered.
- If loading the chunk descs of a series with a known chunkDescsOffset
(i.e. != -1), the number of chunks loaded must be equal to
chunkDescsOffset. If not, there is a data corruption. An error is
returned, which leads to qurantining.
In any case, there is a guard added to not access the 1st element of
an empty chunkDescs slice. (That's what triggered the crashes in issue
2249.) A time series with unknown chunkDescsOffset and no chunks in
memory and no chunks on disk either could trigger that case. I would
assume such a "null series" doesn't exist, but it's not entirely
unthinkable and unreasonable to happen (perhaps in future uses of the
storage). (Create a series, and then something tries to preload chunks
before the first sample is added.)
This extracts Querier as an instantiateable and closeable object
rather than just defining extending methods of the storage interface.
This improves composability and allows abstracting query transactions,
which can be useful for transaction-level caches, consistent data views,
and encapsulating teardown.
When using the chunking code in other projects (both Weave Prism and
ChronixDB ingester), you sometimes want to know how well you are
utilizing your chunks when closing/storing them.
These more specific methods have replaced `metricForLabelMatchers`
in cases where its `map[fingerprint]metric` result type was
not necessary or was used as an intermediate step
Avoids duplicated calls to `seriesForRange` from
`QueryRange` and `QueryInstant` methods.
This is a followup to https://github.com/prometheus/prometheus/pull/2011.
This publishes more of the methods and other names of the chunk code and
moves the chunk code to its own package. There's some unavoidable
ugliness: the chunk and chunkDesc metrics are used by both packages, so
I had to move them to the chunk package. That isn't great, but I don't
see how to do it better without a larger redesign of everything. Same
for the evict requests and some other types.
* Add config, HTTP Basic Auth and TLS support to the generic write path.
- Move generic write path configuration to the config file
- Factor out config.TLSConfig -> tlf.Config translation
- Support TLSConfig for generic remote storage
- Rename Run to Start, and make it non-blocking.
- Dedupe code in httputil for TLS config.
- Make remote queue metrics global.
This is based on https://github.com/prometheus/prometheus/pull/1997.
This adds contexts to the relevant Storage methods and already passes
PromQL's new per-query context into the storage's query methods.
The immediate motivation supporting multi-tenancy in Frankenstein, but
this could also be used by Prometheus's normal local storage to support
cancellations and timeouts at some point.
CPUs have to serialise write access to a single cache line
effectively reducing level of possible parallelism. Placing
mutexes on different cache lines avoids this problem.
Most gains will be seen on NUMA servers where CPU interconnect
traffic is especially expensive
Before:
go test . -run none -bench BenchmarkFingerprintLocker
BenchmarkFingerprintLockerParallel-4 2000000 932 ns/op
BenchmarkFingerprintLockerSerial-4 30000000 49.6 ns/op
After:
go test . -run none -bench BenchmarkFingerprintLocker
BenchmarkFingerprintLockerParallel-4 3000000 569 ns/op
BenchmarkFingerprintLockerSerial-4 30000000 51.0 ns/op
My aim is to support the new grpc generic write path in Frankenstein. On the surface this seems easy - however I've hit a number of problems that make me think it might be better to not use grpc just yet.
The explanation of the problems requires a little background. At weave, traffic to frankenstein need to go through a couple of services first, for SSL and to be authenticated. So traffic goes:
internet -> frontend -> authfe -> frankenstein
- The frontend is Nginx, and adds/removes SSL. Its done this way for legacy reasons, so the certs can be managed in one place, although eventually we imagine we'll merge it with authfe. All traffic from frontend is sent to authfe.
- Authfe checks the auth tokens / cookie etc and then picks the service to forward the RPC to.
- Frankenstein accepts the reads and does the right thing with them.
First problem I hit was Nginx won't proxy http2 requests - it can accept them, but all calls downstream are http1 (see https://trac.nginx.org/nginx/ticket/923). This wasn't such a big deal, so it now looks like:
internet --(grpc/http2)--> frontend --(grpc/http1)--> authfe --(grpc/http1)--> frankenstein
Next problem was golang grpc server won't accept http1 requests (see https://groups.google.com/forum/#!topic/grpc-io/JnjCYGPMUms). It is possible to link a grpc server in with a normal go http mux, as long as the mux server is serving over SSL, as the golang http client & server won't do http2 over anything other than an SSL connection. This would require making all our service to service comms SSL. So I had a go a writing a grpc http1 server, and got pretty far. But is was a bit of a mess.
So finally I thought I'd make a separate grpc frontend for this, running in parallel with the frontend/authfe combo on a different port - and first up I'd need a grpc reverse proxy. Ideally we'd have some nice, generic reverse proxy that only knew about a map from service names -> downstream service, and didn't need to decode & re-encode every request as it went through. It seems like this can't be done with golang's grpc library - see https://github.com/mwitkow/grpc-proxy/issues/1.
And then I was surprised to find you can't do grpc from browsers! See http://www.grpc.io/faq/ - not important to us, but I'm starting to question why we decided to use grpc in the first place?
It would seem we could have most of the benefits of grpc with protos over HTTP, and this wouldn't preclude moving to grpc when its a bit more mature? In fact, the grcp FAQ even admits as much:
> Why is gRPC better than any binary blob over HTTP/2?
> This is largely what gRPC is on the wire.
This adds a flag -storage.local.engine which allows turning off local
storage in Prometheus. Instead of adding if-conditions and nil checks to
all parts of Prometheus that deal with Prometheus's local storage
(including the web interface), disabling local storage simply means
replacing the normal local storage with a noop version that throws
samples away and returns empty query results. We also don't add the noop
storage to the fanout appender to decrease internal overhead.
Instead of returning empty results, an alternate behavior could be to
return errors on any query that point out that the local storage is
disabled. Not sure which one is more preferable, so I went with the
empty result option for now.
By splitting the single queue into multiple queues and flushing each individual queue in serially (and all queues in parallel), we can guarantee to preserve the order of timestampsin samples sent to downstream systems.
- fold metric name into labels
- return initialization errors back to main
- add snappy compression
- better context handling
- pre-allocation of labels
- remove generic naming
- other cleanups
This uses a new proto format, with scope for multiple samples per
timeseries in future. This will allow users to pump samples out to
whatever they like without having to change the core Prometheus code.
There's also an example receiver to save users figuring out the
boilerplate themselves.
Turns out its valid to have an overall chunk which is smaller than the
full doubleDeltaHeaderBytes size -- if it has a single sample, it
doesn't fill the whole header. Updated unmarshalling check to respect
this.
This is (hopefully) a fix for #1653
Specifically, this makes it so that if the length for the stored
delta/doubleDelta is somehow corrupted to be too small, the attempt to
unmarshal will return an error.
The current (broken) behavior is to return a malformed chunk, which can
then lead to a panic when there is an attempt to read header values.
The referenced issue proposed creating chunks with a minimum length -- I
instead opted to just error on the attempt to unmarshal, since I'm not
clear on how it could be safe to proceed when the length is
incorrect/unknown.
The issue also talked about possibly "quarantining series", but I don't
know the surrounding code well enough to understand how to make that
happen.
Specifically, the TestSpawnNotMoreThanMaxConcurrentSendsGoroutines was failing on a fresh checkout of master.
The test had a race condition -- it would only pass if one of the
spawned goroutines happened to very quickly pull a set of samples off an
internal queue.
This patch rewrites the test so that it deterministically waits until
all samples have been pulled off that queue. In case of errors, it also
now reports on the difference between what it expected and what it found.
I verified that, if the code under test is deliberately broken, the test
successfully reports on that.
See discussion in
https://groups.google.com/forum/#!topic/prometheus-developers/bkuGbVlvQ9g
The main idea is that the user of a storage shouldn't have to deal with
fingerprints anymore, and should not need to do an individual preload
call for each metric. The storage interface needs to be made more
high-level to not expose these details.
This also makes it easier to reuse the same storage interface for remote
storages later, as fewer roundtrips are required and the fingerprint
concept doesn't work well across the network.
NOTE: this deliberately gets rid of a small optimization in the old
query Analyzer, where we dedupe instants and ranges for the same series.
This should have a minor impact, as most queries do not have multiple
selectors loading the same series (and at the same offset).
tl;dr: This is not a fundamental solution to the indexing problem
(like tindex is) but it at least avoids utilizing the intersection
problem to the greatest possible amount.
In more detail:
Imagine the following query:
nicely:aggregating:rule{job="foo",env="prod"}
While it uses a nicely aggregating recording rule (which might have a
very low cardinality), Prometheus still intersects the low number of
fingerprints for `{__name__="nicely:aggregating:rule"}` with the many
thousands of fingerprints matching `{job="foo"}` and with the millions
of fingerprints matching `{env="prod"}`. This totally innocuous query
is dead slow if the Prometheus server has a lot of time series with
the `{env="prod"}` label. Ironically, if you make the query more
complicated, it becomes blazingly fast:
nicely:aggregating:rule{job=~"foo",env=~"prod"}
Why so? Because Prometheus only intersects with non-Equal matchers if
there are no Equal matchers. That's good in this case because it
retrieves the few fingerprints for
`{__name__="nicely:aggregating:rule"}` and then starts right ahead to
retrieve the metric for those FPs and checking individually if they
match the other matchers.
This change is generalizing the idea of when to stop intersecting FPs
and go into "retrieve metrics and check them individually against
remaining matchers" mode:
- First, sort all matchers by "expected cardinality". Matchers
matching the empty string are always worst (and never used for
intersections). Equal matchers are in general consider best, but by
using some crude heuristics, we declare some better than others
(instance labels or anything that looks like a recording rule).
- Then go through the matchers until we hit a threshold of remaining
FPs in the intersection. This threshold is higher if we are already
in the non-Equal matcher area as intersection is even more expensive
here.
- Once the threshold has been reached (or we have run out of matchers
that do not match the empty string), start with "retrieve metrics
and check them individually against remaining matchers".
A beefy server at SoundCloud was spending 67% of its CPU time in index
lookups (fingerprintsForLabelPairs), serving mostly a dashboard that
is exclusively built with recording rules. With this change, it spends
only 35% in fingerprintsForLabelPairs. The CPU usage dropped from 26
cores to 18 cores. The median latency for query_range dropped from 14s
to 50ms(!). As expected, higher percentile latency didn't improve that
much because the new approach is _occasionally_ running into the worst
case while the old one was _systematically_ doing so. The 99th
percentile latency is now about as high as the median before (14s)
while it was almost twice as high before (26s).
If the chunks of a series in the checkpoint are all older then the
latest chunk on disk, the head chunk is persisted and therefore has to
be declared closed.
It would be great to have a test for this, but that would require more
plumbing, subject of #447.
PromQL only requires a much narrower interface than local.Storage in
order to run queries. Narrower interfaces are easier to replace and
test, too.
We could also change the web interface to use local.Querier, except that
we'll probably use appending functions from there in the future.
On Windows, it is not possible to rename or delete a file that is
currerntly open. This change closes the file in dropAndPersistChunks
before it tries to delete it, or rename the temporary file to it.
With a lot of series accessed in a short timeframe (by a query, a
large scrape, checkpointing, ...), there is actually quite a
significant amount of lock contention if something similar is running
at the same time.
In those cases, the number of locks needs to be increased.
On the same front, as our fingerprints don't have a lot of entropy, I
introduced some additional shuffling. With the current state, anly
changes in the least singificant bits of a FP would matter.
But only on DEBUG level.
Also, count and report the two cases of out-of-order timestamps on the
one hand and same timestamp but different value on the other hand
separately.
Before, we checkpointed after every newly detected fingerprint
collision, which is not a problem as long as collisions are
rare. However, with a sufficient number of metrics or particular
nature of the data set, there might be a lot of collisions, all to be
detected upon the first set of scrapes, and then the checkpointing
after each detection will take a quite long time (it's O(n²),
essentially).
Since we are rebuilding the fingerprint mapping during crash recovery,
the previous, very conservative approach didn't even buy us
anything. We only ever read from the checkpoint file after a clean
shutdown, so the only time we need to write the checkpoint file is
during a clean shutdown.
Prometheus is Apache 2 licensed, and most source files have the
appropriate copyright license header, but some were missing it without
apparent reason. Correct that by adding it.
The chunk encoding was hardcoded there because it mostly doesn't
matter what encoding is chosen in that test. Since type 1 is
battle-hardened enough, I'm switching to type 2 here so that we can
catch unexpected problems as a byproduct. My expectation is that the
chunk encoding doesn't matter anyway, as said, but then "unexpected
problems" contains the word "unexpected".
So far, the last sample in a chunk was saved twice. That's required
for adding more samples as we need to know the last sample added to
add more samples without iterating through the whole chunk. However,
once the last sample was added to the chunk before it's full, there is
no need to save it twice. Thus, the very last sample added to a chunk
can _only_ be saved in the header fields for the last sample. The
chunk has to be identifiable as closed, then. This information has
been added to the flags byte.
This improves fuzz testing in two ways:
(1) More realistic time stamps. So far, the most common case in
practice was very rare in the test: Completely regular increases of
the timestamp.
(2) Verify samples by scanning through the whole relevant section of
the series.
For Gorilla-like chunks, this showed two things:
(1) With more regularly increasing time stamps, BenchmarkFuzz is
essentially as fast as with the traditional chunks:
```
BenchmarkFuzzChunkType0-8 2 972514684 ns/op 83426196 B/op 2500044 allocs/op
BenchmarkFuzzChunkType1-8 2 971478001 ns/op 82874660 B/op 2512364 allocs/op
BenchmarkFuzzChunkType2-8 2 999339453 ns/op 76670636 B/op 2366116 allocs/op
```
(2) There was a bug related to when and how the chunk footer is
overwritten to make use for the last sample. This wasn't exposed by
random access as the last sample of a chunk is retrieved from the
values in the header in that case.
This is not a verbatim implementation of the Gorilla encoding. First
of all, it could not, even if we wanted, because Prometheus has a
different chunking model (constant size, not constant time). Second,
this adds a number of changes that improve the encoding in general or
at least for the specific use case of Prometheus (and are partially
only possible in the context of Prometheus). See comments in the code
for details.
It is now also used in label matching, so the name of the metric
changed from `prometheus_local_storage_invalid_preload_requests_total`
to `non_existent_series_matches_total'.
Only return an error where callers are doing something with it except
simply logging and ignoring.
All the errors touched in this commit flag the storage as dirty
anyway, and that fact is logged anyway. So most of what is being
removed here is just log spam.
As discussed earlier, the class of errors that flags the storage as
dirty signals fundamental corruption, no even bubbling up a one-time
warning to the user (e.g. about incomplete results) isn't helping much
because _anything_ happening in the storage has to be doubted from
that point on (and in fact retroactively into the past, too). Flagging
the storage dirty, and alerting on it (plus marking the state in the
web UI) is the only way I can see right now.
As a byproduct, I cleaned up the setDirty method a bit and improved
the logged errors.
WIP: This needs more tests.
It now gets a from and through value, which it may opportunistically
use to optimize the retrieval. With possible future range indices,
this could be used in a very efficient way. This change merely applies
some easy checks, which should nevertheless solve the use case of
heavy rule evaluations on servers with a lot of series churn.
Idea is the following:
- Only archive series that are at least as old as the headChunkTimeout
(which was already extremely unlikely to happen).
- Then maintain a high watermark for the last archival, i.e. no
archived series has a sample more recent than that watermark.
- Any query that doesn't reach to a time before that watermark doesn't
have to touch the archive index at all. (A production server at
Soundcloud with the aforementioned series churn and heavy rule
evaluations spends 50% of its CPU time in archive index
lookups. Since rule evaluations usually only touch very recent
values, most of those lookup should disappear with this change.)
- Federation with a very broad label matcher will profit from this,
too.
As a byproduct, the un-needed MetricForFingerprint method was removed
from the Storage interface.
This finally extracts all the common code of the two chunk iterators
into one. Any future chunk encodings with fast access by index can use
the same iterator by simply providing an indexAccessor. Other future
chunk encodings without fast index access (like Gorilla-style) can
still implement the chunkIterator interface as usual.
For one, remove unneeded methods.
Then, instead of using a channel for all values, use a
bufio.Scanner-like interface. This removes the need for creating a
goroutine and avoids the (unnecessary) locking performed by channel
sending and receiving.
This will make it much easier to write new chunk implementations (like
Gorilla-style encoding).
I needed this today for debugging. It can certainly be improved, but
it's already quite helpful.
I refactored the reading of heads.db files out of persistence, which
is an improvement, too.
I made minor changes to the cli package to allow outputting via the
io.Writer interface.
Obviously, it's really bad to depend on timing here. The proper fix
would be to have something like WaitForIndexing for other things to
wait for, too.
For now, let's see if the wait time increase fixes the issue.
This fixes https://github.com/prometheus/prometheus/issues/1059 , but
not in the obvious way (simply not updating the persist watermark,
because that's actually not that simple - we don't really know what
has gone wrong exactly). As any errors relevant here are most likely
caused by severe and unrecoverable problems with the series file,
Using the now quarantine feature is the right step. We don't really
have to be worried about any inconsistent state of the series because
it will be removed for good ASAP. Another plus is that we don't have
to declare the whole storage dirty anymore.
This requires all the panic calls upon unexpected data to be converted
into errors returned. This pollute the function signatures quite
lot. Well, this is Go...
The ideas behind this are the following:
- panic only if it's a programming error. Data corruptions happen, and
they are not programming errors.
- If we detect a data corruption, we "quarantine" the series,
essentially removing it from the database and putting its data into
a separate directory for forensics.
- Failure during writing to a series file is not considered corruption
automatically. It will call setDirty, though, so that a
crashrecovery upon the next restart will commence and check for
that.
- Series quarantining and setDirty calls are logged and counted in
metrics, but are hidden from the user of the interfaces in
interface.go, whith the notable exception of Append(). The reasoning
is that we treat corruption by removing the corrupted series, i.e. a
query for it will return no results on its next call anyway, so
return no results right now. In the case of Append(), we want to
tell the user that no data has been appended, though.
Minor side effects:
- Now consistently using filepath.* instead of path.*.
- Introduced structured logging where I touched it. This makes things
less consistent, but a complete change to structured logging would
be out of scope for this PR.
Fixes https://github.com/prometheus/prometheus/issues/1401
This remove the last (and in fact bogus) use of BoundaryValues.
Thus, a whole lot of unused (and arguably sub-optimal / ugly) code can
be removed here, too.
In a way, our instants were also ranges, just with the staleness delta
as range length. They are no treated equally, just that in one case,
the range length is set as range, in the other the staleness
delta. However, there are "real" instants where start and and time of
a query is the same. In those cases, we only want to return a single
value (the one closest before or at the equal start and end time). If
that value is the last sample in the series, odds are we have it
already in the series object. In that case, there is no need to pin or
load any chunks. A special singleSampleSeriesIterator is created for
that. This should greatly speed up instant queries as they happen
frequently for rule evaluations.
This implies a slight change of behavior as only samples added to the
respective instance of a memorySeries are returned. However, this is
most likely anyway what we want.
Following cases:
- Server has been restarted: Given the time it takes to cleanly
shutdown and start up a server, the series are now stale anyway. An
improved staleness handling (still to be implemented) will be based
on tracking if a given target is continuing to expose samples for a
given time series. In that case, we need a full scrape cycle to
decide about staleness. So again, it makes sense to consider
everything stale directly after a server restart.
- Series unarchived due to a read request: The series is definitely
stale so we don't want to return anything anyway.
- Freshly created time series or series unarchived because of a sample
append: That happens because appending a sample is imminent. Before
the fingerprint lock is released, the series will have received a
sample, and lastSamplePair will always returned the expected value.
Formalize ZeroSamplePair as return value for non-existing samples.
Change LastSamplePairForFingerprint to return a SamplePair (and not a
pointer to it), which saves allocations in a potentially extremely
frequent call.
This will fix issue #1035 and will also help to make issue #1264 less
bad.
The fundamental problem in the current code:
In the preload phase, we quite accurately determine which chunks will
be used for the query being executed. However, in the subsequent step
of creating series iterators, the created iterators are referencing
_all_ in-memory chunks in their series, even the un-pinned ones. In
iterator creation, we copy a pointer to each in-memory chunk of a
series into the iterator. While this creates a certain amount of
allocation churn, the worst thing about it is that copying the chunk
pointer out of the chunkDesc requires a mutex acquisition. (Remember
that the iterator will also reference un-pinned chunks, so we need to
acquire the mutex to protect against concurrent eviction.) The worst
case happens if a series doesn't even contain any relevant samples for
the query time range. We notice that during preloading but then we
will still create a series iterator for it. But even for series that
do contain relevant samples, the overhead is quite bad for instant
queries that retrieve a single sample from each series, but still go
through all the effort of series iterator creation. All of that is
particularly bad if a series has many in-memory chunks.
This commit addresses the problem from two sides:
First, it merges preloading and iterator creation into one step,
i.e. the preload call returns an iterator for exactly the preloaded
chunks.
Second, the required mutex acquisition in chunkDesc has been greatly
reduced. That was enabled by a side effect of the first step, which is
that the iterator is only referencing pinned chunks, so there is no
risk of concurrent eviction anymore, and chunks can be accessed
without mutex acquisition.
To simplify the code changes for the above, the long-planned change of
ValueAtTime to ValueAtOrBefore time was performed at the same
time. (It should have been done first, but it kind of accidentally
happened while I was in the middle of writing the series iterator
changes. Sorry for that.) So far, we actively filtered the up to two
values that were returned by ValueAtTime, i.e. we invested work to
retrieve up to two values, and then we invested more work to throw one
of them away.
The SeriesIterator.BoundaryValues method can be removed once #1401 is
fixed. But I really didn't want to load even more changes into this
PR.
Benchmarks:
The BenchmarkFuzz.* benchmarks run 83% faster (i.e. about six times
faster) and allocate 95% fewer bytes. The reason for that is that the
benchmark reads one sample after another from the time series and
creates a new series iterator for each sample read.
To find out how much these improvements matter in practice, I have
mirrored a beefy Prometheus server at SoundCloud that suffers from
both issues #1035 and #1264. To reach steady state that would be
comparable, the server needs to run for 15d. So far, it has run for
1d. The test server currently has only half as many memory time series
and 60% of the memory chunks the main server has. The 90th percentile
rule evaluation cycle time is ~11s on the main server and only ~3s on
the test server. However, these numbers might get much closer over
time.
In addition to performance improvements, this commit removes about 150
LOC.
The First time is kind of trivial as we always know it when we create
a new chunkDesc.
The last time is only know when the chunk is closed, so we have to set
it at that time.
The change saves a lot of digging down into the chunk
itself. Especially the last time is relative expensive as it involves
the creation of an iterator. The first time access now doesn't require
locking, which is also a nice gain.
This gives up on the idea to communicate throuh the Append() call (by
either not returning as it is now or returning an error as
suggested/explored elsewhere). Here I have added a Throttled() call,
which has the advantage that it can be called before a whole _batch_
of Append()'s. Scrapes will happen completely or not at all. Same for
rule group evaluations. That's a highly desired behavior (as discussed
elsewhere). The code is even simpler now as the whole ingestion buffer
could be removed.
Logging of throttled mode has been streamlined and will create at most
one message per minute.
Since we are not overestimating the number of chunks to persist
anymore, this commit also adjusts the default value for
-storage.local.memory-chunks. Update of documentation will follow.
"Rushed mode" is formerly known as "degraded mode", which is changed
with this commit, too. The name "degraded" was very misleading.
Also, switch into rushed mode if we have too many chunks in memory and
an at least reasonable amount of chunks to persist so that speeding up
persisting chunks can help.
If only very few chunks are to be truncated from a very large series
file, the rewrite of the file is a lorge overhead. With this change, a
certain ratio of the file has to be dropped to make it happen. While
only causing disk overhead at about the same ratio (by default 10%),
it will cut down I/O by a lot in above scenario.
Allows to use graphite over tcp or udp. Metrics labels
and values are used to construct a valid Graphite path
in a way that will allow us to eventually read them back
and reconstruct the metrics.
For example, this metric:
model.Metric{
model.MetricNameLabel: "test:metric",
"testlabel": "test:value",
"testlabel2": "test:value",
)
Will become:
test:metric.testlabel=test:value.testlabel2=test:value
escape.go takes care of escaping values to match Graphite
character set, it basically uses percent-encoding as a fallback
wich will work pretty will in the graphite/grafana world.
The remote storage module also has an optional 'prefix' parameter
to prefix all metrics with a path (for example, 'prometheus.').
Graphite URLs are simply in the form tcp://host:port or
udp://host:port.
Because the InfluxDB client library currently pulls in multiple MBs of
unnecessary dependencies, I have modified and cut up the vendored
version to only pull in the few pieces that are actually needed.
On InfluxDB's side, this dependency issue is tracked in:
https://github.com/influxdb/influxdb/issues/3447
Hopefully, it will be resolved soon.
If a password is needed for InfluxDB, it may be supplied via the
INFLUXDB_PW environment variable.
The test had become flaky with Go1.5.
Theory here is that with Go1.5.x, sleeping for 10ms might not be
enough to wake up another goroutine, possibly because it is used for
GC. 50ms should always be enough due to GC pause guarantees with the
new GC.
This is with `golint -min_confidence=0.5`.
I left several lint warnings untouched because they were either
incorrect or I felt it was better not to change them at the moment.
If users see the crash recovery error, the chances are
they aren't shutting down Prometheus correctly. Telling
them how to do so will help them debug and fix the problem.
Perhaps it would be even better to still warn in case the sample value has
changed but the timestamps are equal, but we don't have efficient access
to the last value.
Allow scrape_configs to have an optional proxy_url option which specifies
a proxy to be used for all connections to hosts in that config.
Internally this modifies the various client functions to take a *url.URL pointer
which currently must point to an HTTP proxy (but has been left open-ended to
allow the url format to be extended to support others, such as maybe SOCKS if
needed).
For the label matching index-based preselection phase, don't do an OR
between equality and non-equality matchers. Execute only one of the two
(with equality matchers preferred when present).
Fixes https://github.com/prometheus/prometheus/issues/924
If all samples in consecutive chunks have the same timestamp, the way
we used to load chunks will fail. With this change, the persist
watermark is used to load the right amount of chunkDescs from disk.
This bug is a possible reason for the rare storage corruption we have
observed.
Fixes https://github.com/prometheus/prometheus/issues/481
While doing so, clean up and fix a few other things:
- Fix `go vet` warnings (@fabxc to blame ;).
- Fix a racey problem with unarchiving: Whenever we unarchive a
series, we essentially want to do something with it. However, until
we have done something with it, it appears like a series that is
ready to be archived or even purged. So e.g. it would be ignored
during checkpointing. With this fix, we always load the chunkDescs
upon unarchiving. This is wasteful if we only want to add a new
sample to an archived time series, but the (presumably more common)
case where we access an archived time series in a query doesn't
become more expensive.
- The change above streamlined the getOrCreateSeries ond
newMemorySeries flow. Also, the modTime is now always set correctly.
- Fix the leveldb-backed implementation of KeyValueStore.Delete. It
had the wrong behavior of still returning true, nil if a
non-existing key has been passed in.
See https://github.com/prometheus/prometheus/issues/887, which will at
least be partially fixed by this.
From the spec https://golang.org/ref/spec#Conversions:
"In all non-constant conversions involving floating-point or complex
values, if the result type cannot represent the value the conversion
succeeds but the result value is implementation-dependent."
This ended up setting the converted values to 0 on Debian's Go 1.4.2
compiler, at least on 32-bit Debians.
This commit adds the honor_labels and params arguments to the scrape
config. This allows to specify query parameters used by the scrapers
and handling scraped labels with precedence.
Change #704 introduced a regression that started reading the queue only
after potential crash recovery. When more than the queue capacity was
indexed, Prometheus deadlocked.
This change is conceptually very simple, although the diff is large. It
switches logging from "github.com/golang/glog" to
"github.com/prometheus/log", while not actually changing any log
messages. V(1)-style logging has been changed to be log.Debug*().
This commit creates a (so far unused) package. It contains the a custom
lexer/parser for the query language.
ast.go: New AST that interacts well with the parser.
lex.go: Custom lexer (new).
lex_test.go: Lexer tests (new).
parse.go: Custom parser (new).
parse_test.go: Parser tests (new).
functions.go: Changed function type, dummies for parser testing (barely changed/dummies).
printer.go: Adapted from rules/ and adjusted to new AST (mostly unchanged, few additions).
Also, clean up some things in the code (especially introduction of the
chunkLenWithHeader constant to avoid the same expression all over the place).
Benchmark results:
BEFORE
BenchmarkLoadChunksSequentially 5000 283580 ns/op 152143 B/op 312 allocs/op
BenchmarkLoadChunksRandomly 20000 82936 ns/op 39310 B/op 99 allocs/op
BenchmarkLoadChunkDescs 10000 110833 ns/op 15092 B/op 345 allocs/op
AFTER
BenchmarkLoadChunksSequentially 10000 146785 ns/op 152285 B/op 315 allocs/op
BenchmarkLoadChunksRandomly 20000 67598 ns/op 39438 B/op 103 allocs/op
BenchmarkLoadChunkDescs 20000 99631 ns/op 12636 B/op 192 allocs/op
Note that everything is obviously loaded from the page cache (as the
benchmark runs thousands of times with very small series files). In a
real-world scenario, I expect a larger impact, as the disk operations
will more often actually hit the disk. To load ~50 sequential chunks,
this reduces the iops from 100 seeks and 100 reads to 1 seek and 1
read.
The one central sample ingestion channel has caused a variety of
trouble. This commit removes it. Targets and rule evaluation call an
Append method directly now. To incorporate multiple storage backends
(like OpenTSDB), storage.Tee forks the Append into two different
appenders.
Note that the tsdb queue manager had its own queue anyway. It was a
queue after a queue... Much queue, so overhead...
Targets have their own little buffer (implemented as a channel) to
avoid stalling during an http scrape. But a new scrape will only be
started once the old one is fully ingested.
The contraption of three pipelined ingesters was removed. A Target is
an ingester itself now. Despite more logic in Target, things should be
less confusing now.
Also, remove lint and vet warnings in ast.go.
A number of mostly minor things:
- Rename chunk type -> chunk encoding.
- After all, do not carry around the chunk encoding to all parts of
the system, but just have one place where the encoding for new
chunks is set based on the flag. The new approach has caveats as
well, but the polution of so many method signatures is worse.
- Use the default chunk encoding for new chunks of existing
series. (Previously, only new _series_ would get chunks with the
default encoding.)
- Use an enum for chunk encoding. (But keep the version number for the
flag, for reasons discussed previously.)
- Add encoding() to the chunk interface (so that a chunk knows its own
encoding - no need to have that in a different top-level function).
- Got rid of newFollowUpChunk (which would keep the existing encoding
for all chunks of a time series). Now only use newChunk(), which
will create a chunk encoding according to the flag.
- Simplified transcodeAndAdd.
- Reordered methods of deltaEncodedChunk and doubleDeltaEncoded chunk
to match the order in the chunk interface.
- Only transcode if the chunk is not yet half full. If more than half
full, add a new chunk instead.
This checks for the basic behaviour of GetFingerprintsForLabelMatchers, that is, whether the different matcher types filter the correct fingerprints and intersections are correct.
The capacity is basically how many persisted head chunks we will count
at most while doing other things, in particular checkpointing. To
limit the amount of already counted head chunks, keep this number low,
otherwise we will easily checkpoint too often if checkpoints take long
anyway.
In that commit, the 'maintainSeries' call was accidentally removed.
This commit refactors things a bit so that there is now a clean
'maintainMemorySeries' and a 'maintainArchivedSeries' call.
Straighten the nomenclature a bit (consistently use 'drop' for
chunks and 'purge' for series/metrics).
Remove the annoying 'Completed maintenance sweep through archived
fingerprints' message if there were no archived fingerprints to do
maintenance on.
This is done by bucketing chunks by fingerprint. If the persisting to
disk falls behind, more and more chunks are in the queue. As soon as
there are "double hits", we will now persist both chunks in one go,
doubling the disk throughput (assuming it is limited by disk
seeks). Should even more pile up so that we end wit "triple hits", we
will persist those first, and so on.
Even if we have millions of time series, this will still help,
assuming not all of them are growing with the same speed. Series that
get many samples and/or are not very compressable will accumulate
chunks faster, and they will soon get double- or triple-writes.
To improve the chance of double writes,
-storage.local.persistence-queue-capacity could be set to a higher
value. However, that will slow down shutdown a lot (as the queue has
to be worked through). So we leave it to the user to set it to a
really high value. A more fundamental solution would be to checkpoint
not only head chunks, but also chunks still in the persist queue. That
would be quite complicated for a rather limited use-case (running many
time series with high ingestion rate on slow spinning disks).
Starting a goroutine takes 1-2µs on my laptop. From the "numbers every
Go programmer should know", I had 300ns for a channel send in my
mind. Turns out, on my laptop, it takes only 60ns. That's fast enough
to warrant the machinery of yet another channel with a fixed set of
worker goroutines feeding from it. The number chosen (8 for now) is
low enough to not really afflict a measurable overhead (a big
Prometheus server has >1000 goroutines running), but high enough to
not make sample ingestion a bottleneck.
- Parallelize AppendSamples as much as possible without breaking the
contract about temporal order.
- Allocate more fingerprint locker slots.
- Do not run early checkpoints if we are behind on chunk persistence.
- Increase fpMinWaitDuration to give the disk more time for more
important things.
Also, switch math.MaxInt64 and math.MinInt64 to the new constants.
Also, set a much higher default value.
Chunk persist requests can be quite spiky. If you collect a large
number of time series that are very similar, they will tend to finish
up a chunk at about the same time. There is no reason we need to back
up scraping just because of that. The rationale of the new default
value is "1/8 of the chunks in memory".
persistence.go is way too long anyway, and a lot of code is just crash
recovery, which is not important to understand the normal operation.
Also, remove unused `exists` function.
Previously, it would return an error instead. Now we can distinguish
the cases 'error while deleting known key' vs. 'key not in index'
without testing for leveldb-internal kinds of errors.
If queries are still running when the shutdown is initiated, they will
finish _during_ the shutdown. In that case, they might request chunk
eviction upon unpinning their pinned chunks. That might completely
fill the evict request queue _after_ draining it during storage
shutdown. If that ever happens (which is the case if there are _many_
queries still running during shutdown), the affected queries will be
stuck while keeping a fingerprint locked. The checkpointing can then
not process that fingerprint (or one that shares the same lock). And
then we are deadlocked.
- Move CONTRIBUTORS.md to the more common AUTHORS.
- Added the required NOTICE file.
- Changed "Prometheus Team" to "The Prometheus Authors".
- Reverted the erroneous changes to the Apache License.
This mimics the locking leveldb is performing anyway. Advantages of
doing it separately:
- Should we ever replace the leveldb implementation by one without
double-start protection, we are still good.
- In contrast to leveldb, the new code creates a meaningful error
message.
Usually, if you unarchive a series, it is to add something to it,
which will create a new head chunk. However, if a series in
unarchived, and before anything is added to it, it is handled by the
maintenance loop, it will be archived again. In that case, we have to
load the chunkDescs to know the lastTime of the series to be
archived. Usually, this case will happen only rarely (as a race, has
never happened so far, possibly because the locking around unarchiving
and the subsequent sample append is smart enough). However, during
crash recovery, we sometimes treat series as "freshly unarchived"
without directly appending a sample. We might add more cases of that
type later, so better deal with archiving properly and load chunkDescs
if required.
- Documented checkpoint file format.
- High-level description of series sanitation.
- Replace fp.LoadFromString panic with an error.
(Change in client_golang already submitted.)
- Introduced checks for series file size where appropriate.
- Removed two Law of Demeter violations.
Change-Id: I555d97a2c8f4769820c2fc8bf5d6f4e160222abc
- Delete unneeded file view_adapter.go.
- Assessed that we still need the fingerprints in nodes
(to create iterators).
- Turned numMemChunkDescs into a metric.
Change-Id: I29be963c795a075ec00c095f76bf26405535609d
Now only purge if there is something to purge.
Also, set savedFirstTime and archived time range appropriately.
(Which is needed for the optimization.)
Change-Id: Idcd33319a84def3ce0318d886f10c6800369e7f9
Fix the behavior if preload for non-existent series is requested.
Instead of returning an error (which triggers a panic further up),
simply count those incidents. They can happen regularly, we just want
to know if they happen too frequently because that would mean the
indexing is behind or broken.
Change-Id: I4b2d1b93c4146eeea897d188063cb9574a270f8b
The root cause was that after chunkDesc eviction, the offset between
memory representation of chunk layout (via chunkDescs in memory) was
shiftet against chunks as layed out on disk. Keeping the offset up to
date is by no means trivial, so this commit is pretty involved.
Also, found a race that for some reason didn't bite us so far:
Persisting chunks was completel unlocked, so if chunks were purged on
disk at the same time, disaster would strike. However, locking the
persisting of chunk revealed interesting dead locks. Basically, never
queue under the fp lock.
Change-Id: I1ea9e4e71024cabbc1f9601b28e74db0c5c55db8
Checkpointing interval is now a command line flag.
Along the way, several things were refactored.
- Restructure the way the storage is started and stopped..
- Number of series in checkpoint is now a uint64, not a varint.
(Breaks old checkpoints, needs wipe!)
- More consistent naming and order of methods.
Change-Id: I883d9170c9a608ee716bb0ab3d0ded8ca03760d9
Add gauge for chunks and chunkdescs in memory (backed by a global
variable to be used later not only for instrumentation but also for
memory management).
Refactored instrumentation code once more (instrumentation.go is back :).
Change-Id: Ife39947e22a48cac4982db7369c231947f446e17
- Staleness delta is no a proper function parameter and not replicated
from package ast.
- Named type 'chunks' replaced by explicit '[]chunk' to avoid confusion.
- For the same reason, replaced 'chunkDescs' by '[]*chunkDescs'.
- Verified that math.Modf is not a speed enhancement over conversion
(actually 5x slower).
- Renamed firstTimeField, lastTimeField into chunkFirstTime and
chunkLastTime.
- Verified unpin() is sufficiently goroutine-safe.
- Decided not to update archivedFingerprintToTimeRange upon series
truncation and added a rationale why.
Change-Id: I863b8d785e5ad9f71eb63e229845eacf1bed8534
- Head chunk persisting only happens in evictOlderThan, so do it
there. (With the previous code, it would never happen.)
- Raw accesses to chunkDesc.chunk are now done via isEvicted (with
locking).
Change-Id: I48b07b56dfea4899b50df159b4ea566954396fcd
Also, fix problems in shutdown.
Starting serving and shutdown still has to be cleaned up properly.
It's a mess.
Change-Id: I51061db12064e434066446e6fceac32741c4f84c
Some other improvements on the way, in particular codec -> codable
renaming and addition of LookupSet methods.
Change-Id: I978f8f3f84ca8e4d39a9d9f152ae0ad274bbf4e2
Most important, the heads file will now persist all the chunk descs,
too. Implicitly, it will serve as the persisted form of the
fp-to-series map.
Change-Id: Ic867e78f2714d54c3b5733939cc5aef43f7bd08d
BinaryMarshaler instead of encodable.
BinaryUnmarshaler instead of decodable.
Left 'codable' in place for lack of a better word.
Change-Id: I8a104be7d6db916e8dbc47ff95e6ff73b845ac22
Large delta values often imply a difference between a large base value
and the large delta value, potentially resulting in small numbers with
a huge precision error. Since large delta values need 8 bytes anyway,
we are not even saving memory.
As a solution, always save the absoluto value rather than a delta once
8 bytes would be needed for the delta. Timestamps are then saved as 8
byte integers, while values are always saved as float64 in that case.
Change-Id: I01100d600515e16df58ce508b50982ffd762cc49
Go downloads moved to a different URL and require following redirects
(curl's '-L' option) now.
Go 1.3 deliberately randomizes ranges over maps, which uncovered some
bugs in our tests. These are fixed too.
Change-Id: Id2d9e185d8d2379a9b7b8ad5ba680024565d15f4
- Always spell out the time unit (e.g. milliseconds instead of ms).
- Remove "_total" from the names of metrics that are not counters.
- Make use of the "Namespace" and "Subsystem" fields in the options.
- Removed the "capacity" facet from all metrics about channels/queues.
These are all fixed via command line flags and will never change
during the runtime of a process. Also, they should not be part of
the same metric family. I have added separate metrics for the
capacity of queues as convenience. (They will never change and are
only set once.)
- I left "metric_disk_latency_microseconds" unchanged, although that
metric measures the latency of the storage device, even if it is not
a spinning disk. "SSD" is read by many as "solid state disk", so
it's not too far off. (It should be "solid state drive", of course,
but "metric_drive_latency_microseconds" is probably confusing.)
- Brian suggested to not mix "failure" and "success" outcome in the
same metric family (distinguished by labels). For now, I left it as
it is. We are touching some bigger issue here, especially as other
parts in the Prometheus ecosystem are following the same
principle. We still need to come to terms here and then change
things consistently everywhere.
Change-Id: If799458b450d18f78500f05990301c12525197d3
The first sort in groupByFingerprint already ensures that all resulting sample
lists contain only one fingerprint. We also already assume that all
samples passed into AppendSamples (and thus groupByFingerprint) are
chronologically sorted within each fingerprint.
The extra chronological sort is thus superfluous. Furthermore, this
second sort didn't only sort chronologically, but also compared all
metric fingerprints again (although we already know that we're only
sorting within samples for the same fingerprint). This caused a huge
memory and runtime overhead.
In a heavily loaded real Prometheus, this brought down disk flush times
from ~9 minutes to ~1 minute.
OLD:
BenchmarkLevelDBAppendRepeatingValues 5 331391808 ns/op 44542953 B/op 597788 allocs/op
BenchmarkLevelDBAppendsRepeatingValues 5 329893512 ns/op 46968288 B/op 3104373 allocs/op
NEW:
BenchmarkLevelDBAppendRepeatingValues 5 299298635 ns/op 43329497 B/op 567616 allocs/op
BenchmarkLevelDBAppendsRepeatingValues 20 92204601 ns/op 1779454 B/op 70975 allocs/op
Change-Id: Ie2d8db3569b0102a18010f9e106e391fda7f7883
This fixes the problem where samples become temporarily unavailable for
queries while they are being flushed to disk. Although the entire
flushing code could use some major refactoring, I'm explicitly trying to
do the minimal change to fix the problem since there's a whole new
storage implementation in the pipeline.
Change-Id: I0f5393a30b88654c73567456aeaea62f8b3756d9
Move rulemanager to it's own package to break cicrular dependency.
Make NewTestTieredStorage available to tests, remove duplication.
Change-Id: I33b321245a44aa727bfc3614a7c9ae5005b34e03
This optimizes the runtime and memory allocation behavior for label matchers
other than type "Equal". Instead of creating a new set for every union of
fingerprints, this simply adds new fingerprints to the existing set to achieve
the same effect.
The current behavior made a production Prometheus unresponsive when running a
NotEqual match against the "instance" label (a label with high value
cardinality).
BEFORE:
BenchmarkGetFingerprintsForNotEqualMatcher 10 170430297 ns/op 39229944 B/op 40709 allocs/op
AFTER:
BenchmarkGetFingerprintsForNotEqualMatcher 5000 706260 ns/op 217717 B/op 1116 allocs/op
Change-Id: Ifd78e81e7dfbf5d7249e50ad1903a5d9c42c347a
This fixes https://github.com/prometheus/prometheus/issues/390
The cause for the deadlock was a lock semantic in Go that wasn't
obvious to me when introducing this bug:
http://golang.org/pkg/sync/#RWMutex.Lock
Key phrase: "To ensure that the lock eventually becomes available, a
blocked Lock call excludes new readers from acquiring the lock."
In the memory series storage, we have one function
(GetFingerprintsForLabelMatchers) acquiring an RLock(), which calls
another function also acquiring the same RLock()
(GetLabelValuesForLabelName). That normally doesn't deadlock, unless a
Lock() call from another goroutine happens right in between the two
RLock() calls, blocking both the Lock() and the second RLock() call from
ever completing.
GoRoutine 1 GoRoutine 2
======================================
RLock()
... Lock() [DEADLOCK]
RLock() [DEADLOCK] Unlock()
RUnlock()
RUnlock()
Testing deadlocks is tricky, but the regression test I added does
reliably detect the deadlock in the original code on my machine within a
normal concurrent reader/writer run duration of 250ms.
Change-Id: Ib34c2bb8df1a80af44550cc2bf5007055cdef413
This was initially motivated by wanting to distribute the rule checker
tool under `tools/rule_checker`. However, this was not possible without
also distributing the LevelDB dynamic libraries because the tool
transitively depended on Levigo:
rule checker -> query layer -> tiered storage layer -> leveldb
This change separates external storage interfaces from the
implementation (tiered storage, leveldb storage, memory storage) by
putting them into separate packages:
- storage/metric: public, implementation-agnostic interfaces
- storage/metric/tiered: tiered storage implementation, including memory
and LevelDB storage.
I initially also considered splitting up the implementation into
separate packages for tiered storage, memory storage, and LevelDB
storage, but these are currently so intertwined that it would be another
major project in itself.
The query layers and most other parts of Prometheus now have notion of
the storage implementation anymore and just use whatever implementation
they get passed in via interfaces.
The rule_checker is now a static binary :)
Change-Id: I793bbf631a8648ca31790e7e772ecf9c2b92f7a0
We are not reusing buffers yet. This could introduce problems,
so the behavior is disabled for now.
Cursory benchmark data:
- Marshal for 10,000 samples: -30% overhead.
- Unmarshal for 10,000 samples: -15% overhead.
Change-Id: Ib006bdc656af45dca2b92de08a8f905d8d728cac
The format header size is not deducted from the size of the byte
stream when calculating the output buffer size for samples. I have
yet to notice problems directly as a result of this, but it is good
to fix.
Change-Id: Icb07a0718366c04ddac975d738a6305687773af0
The idiomatic pattern for signalling a one-time message to multiple
consumers from a single producer is as follows:
```
c := make(chan struct{})
w := new(sync.WaitGroup) // Boilerplate to ensure synchronization.
for i := 0; i < 1000; i++ {
w.Add(1)
go func() {
defer w.Done()
for {
select {
case _, ok := <- c:
if !ok {
return
}
default:
// Do something here.
}
}
}()
}
close(c) // Signal the one-to-many single-use message.
w.Wait()
```
Change-Id: I755f73ba4c70a923afd342a4dea63365bdf2144b
There are four label-matching ops for selecting timeseries now:
- Equal: =
- NotEqual: !=
- RegexMatch: =~
- RegexNoMatch: !~
Instead of looking up labels by a simple clientmodel.LabelSet (basically
an equals op for every key/value pair in the set), timeseries
fingerprint selection is now done via a list of metric.LabelMatchers.
Change-Id: I510a83f761198e80946146770ebb64e4abc3bb96
In the case that a getValuesAtIntervalOp's ExtractSamples() is called
with a current time after the last chunk time, we return without
extracting any further values beyond the last one in the chunk
(correct), but also without advancing the op's time (incorrect). This
leads to an infinite loop in renderView(), since the op is called
repeatedly without ever being advanced and consumed.
This adds handling for this special case. When detecting this case, we
immediately set the op to be consumed, since we would always get a value
after the current time passed in if there was one.
Change-Id: Id99149e07b5188d655331382b8b6a461b677005c
This fixes a bug where an interval op might advance too far past the end
of the currently extracted chunk, effectively skipping over relevant
(to-be-extracted) values in the subsequent chunk. The result: missing
samples at chunk boundaries in the resulting view.
Change-Id: Iebf5d086293a277d330039c69f78e1eaf084b3c8
This also fixes the compaction test, which before worked only because
the input sample sorting was accidentally equal to the resulting on-disk
sample sorting.
Change-Id: I2a21c4b46ba562424b27058fc02eba84fa6a6006
- Most of this is the actual regression test in tiered_test.go.
- Working on that regression tests uncovered problems in
tiered_test.go that are fixed in this commit.
- The 'op.consumed = false' line added to freelist.go was actually not
fixing a bug. Instead, there was no bug at all. So this commit
removes that line again, but adds a regression test to make sure
that the assumed bug is indeed not there (cf. freelist_test.go).
- Removed more code duplication in operation.go (following the same
approach as before, i.e. embedding op type A into op type B if
everything in A is the same as in B with the exception of String()
and ExtractSample()). (This change make struct literals for ops more
clunky, but that only affects tests. No code change whatsoever was
necessary in the actual code after this refactoring.)
- Fix another op leak in tiered.go.
Change-Id: Ia165c52e33290ad4f6aba9c83d92318d4f583517
The initial impetus for this was that it made unmarshalling sample
values much faster.
Other relevant benchmark changes in ns/op:
Benchmark old new speedup
==================================================================
BenchmarkMarshal 179170 127996 1.4x
BenchmarkUnmarshal 404984 132186 3.1x
BenchmarkMemoryGetValueAtTime 57801 50050 1.2x
BenchmarkMemoryGetBoundaryValues 64496 53194 1.2x
BenchmarkMemoryGetRangeValues 66585 54065 1.2x
BenchmarkStreamAdd 45.0 75.3 0.6x
BenchmarkAppendSample1 1157 1587 0.7x
BenchmarkAppendSample10 4090 4284 0.95x
BenchmarkAppendSample100 45660 44066 1.0x
BenchmarkAppendSample1000 579084 582380 1.0x
BenchmarkMemoryAppendRepeatingValues 22796594 22005502 1.0x
Overall, this gives us good speedups in the areas where they matter
most: decoding values from disk and accessing the memory storage (which
is also used for views).
Some of the smaller append examples take minimally longer, but the cost
seems to get amortized over larger appends, so I'm not worried about
these. Also, we're currently not bottlenecked on the write path and have
plenty of other optimizations available in that area if it becomes
necessary.
Memory allocations during appends don't change measurably at all.
Change-Id: I7dc7394edea09506976765551f35b138518db9e8
This doesn't add complex discriminator logic yet, but adds a single
version byte to the beginning of each samples chunk. If we ever need to
change the disk format again, this will make it easy to do so without
having to wipe the entire database.
Change-Id: I60c39274256f790bc2da83167a1effaa174588fe
This fixes https://github.com/prometheus/prometheus/issues/381.
For any stale series we dropped from memory, this bug caused us to also drop
any other series from the labelpair->fingerprints memory index if they had any
label/value-pairs in common with the intentionally dropped series.
To fix this issue more easily, I converted the labelpair->fingerprints index
map values to a utility.Set of clientmodel.Fingerprints. This makes handling
this index much easier in general.
Change-Id: If5e81e202e8c542261bbd9797aa1257376c5c074
Currently, rendering a view is capable of handling multiple ops for
the same fingerprint efficiently. However, this capability requires a
lot of complexity in the code, which we are not using at all because
the way we assemble a viewRequest will never have more than one
operation per fingerprint.
This commit weeds out the said capability, along with all the code
needed for it. It is still possible to have more than one operation
for the same fingerprint, it will just be handled in a less efficient
way (as proven by the unit tests).
As a result, scanjob.go could be removed entirely.
This commit also contains a few related refactorings and removals of
dead code in operation.go, view,go, and freelist.go. Also, the
docstrings received some love.
Change-Id: I032b976e0880151c3f3fdb3234fb65e484f0e2e5
We have seven different types all called like LevelDB.*Options. One
of them is the plain LevelDBOptions. All others are just wrapping that
type without adding anything except clunkier handling.
If there ever was a plan to add more specific options to the various
LevelDB.*Options types, history has proven that nothing like that is
going to happen anytime soon.
To keep the code a bit shorter and more focused on the real (quite
significant) complexities we have to deal with here, this commit
reduces all uses of LevelDBOptions to the actual LevelDBOptions type.
1576 fewer characters to read...
Change-Id: I3d7a2b7ffed78b337aa37f812c53c058329ecaa6
- Mostly docstring fixed/additions.
(Please review these carefully, since most of them were missing, I
had to guess them from an outsider's perspective. (Which on the
other hand proves how desperately required many of these docstrings
are.))
- Removed all uses of new(...) to meet our own style guide (draft).
- Fixed all other 'go vet' and 'golint' issues (except those that are
not fixable (i.e. caused by bugs in or by design of 'go vet' and
'golint')).
- Some trivial refactorings, like reorder functions, minor renames, ...
- Some slightly less trivial refactoring, mostly to reduce code
duplication by embedding types instead of writing many explicit
forwarders.
- Cleaned up the interface structure a bit. (Most significant probably
the removal of the View-like methods from MetricPersistenc. Now they
are only in View and not duplicated anymore.)
- Removed dead code. (Probably not all of it, but it's a first
step...)
- Fixed a leftover in storage/metric/end_to_end_test.go (that made
some parts of the code never execute (incidentally, those parts
were broken (and I fixed them, too))).
Change-Id: Ibcac069940d118a88f783314f5b4595dce6641d5
Problem description:
====================
If a rule evaluation referencing a metric/timeseries M happens at a time
when M doesn't have a memory timeseries yet, looking up the fingerprint
for M (via TieredStorage.GetMetricForFingerprint()) will create a new
Metric object for M which gets both: a) attached to a new empty memory
timeseries (so we don't have to ask disk for the Metric's fingerprint
next time), and b) returned to the rule evaluation layer. However, the
rule evaluation layer replaces the name label (and possibly other
labels) of the metric with the name of the recorded rule. Since both
the rule evaluator and the memory storage share a reference to the same
Metric object, the original memory timeseries will now also be
incorrectly renamed.
Fix:
====
Instead of storing a reference to a shared metric object, take a copy of
the object when creating an empty memory timeseries for caching
purposes.
Change-Id: I9f2172696c16c10b377e6708553a46ef29390f1e
The storage itself should be closed before any of the objects passed into it
are closed (otherwise closing the storage can randomly freeze). Defers are
executed in reverse order, so closing the storage should be the last of the
defer statements.
Change-Id: Id920318b876f5b94767ed48c81221b3456770620
This used to work with Go 1.1, but only because of a compiler bug.
The bug is fixed in Go 1.2, so we have to fix our code now.
Change-Id: I5a9f3a15878afd750e848be33e90b05f3aa055e1
Prometheus needs long-term storage. Since we don't have enough resources
to build our own timeseries storage from scratch ontop of Riak,
Cassandra or a similar distributed datastore at the moment, we're
planning on using OpenTSDB as long-term storage for Prometheus. It's
data model is roughly compatible with that of Prometheus, with some
caveats.
As a first step, this adds write-only replication from Prometheus to
OpenTSDB, with the following things worth noting:
1)
I tried to keep the integration lightweight, meaning that anything
related to OpenTSDB is isolated to its own package and only main knows
about it (essentially it tees all samples to both the existing storage
and TSDB). It's not touching the existing TieredStorage at all to avoid
more complexity in that area. This might change in the future,
especially if we decide to implement a read path for OpenTSDB through
Prometheus as well.
2)
Backpressure while sending to OpenTSDB is handled by simply dropping
samples on the floor when the in-memory queue of samples destined for
OpenTSDB runs full. Prometheus also only attempts to send samples once,
rather than implementing a complex retry algorithm. Thus, replication to
OpenTSDB is best-effort for now. If needed, this may be extended in the
future.
3)
Samples are sent in batches of limited size to OpenTSDB. The optimal
batch size, timeout parameters, etc. may need to be adjusted in the
future.
4)
OpenTSDB has different rules for legal characters in tag (label) values.
While Prometheus allows any characters in label values, OpenTSDB limits
them to a to z, A to Z, 0 to 9, -, _, . and /. Currently any illegal
characters in Prometheus label values are simply replaced by an
underscore. Especially when integrating OpenTSDB with the read path in
Prometheus, we'll need to reconsider this: either we'll need to
introduce the same limitations for Prometheus labels or escape/encode
illegal characters in OpenTSDB in such a way that they are fully
decodable again when reading through Prometheus, so that corresponding
timeseries in both systems match in their labelsets.
Change-Id: I8394c9c55dbac3946a0fa497f566d5e6e2d600b5
So far we've been using Go's native time.Time for anything related to sample
timestamps. Since the range of time.Time is much bigger than what we need, this
has created two problems:
- there could be time.Time values which were out of the range/precision of the
time type that we persist to disk, therefore causing incorrectly ordered keys.
One bug caused by this was:
https://github.com/prometheus/prometheus/issues/367
It would be good to use a timestamp type that's more closely aligned with
what the underlying storage supports.
- sizeof(time.Time) is 192, while Prometheus should be ok with a single 64-bit
Unix timestamp (possibly even a 32-bit one). Since we store samples in large
numbers, this seriously affects memory usage. Furthermore, copying/working
with the data will be faster if it's smaller.
*MEMORY USAGE RESULTS*
Initial memory usage comparisons for a running Prometheus with 1 timeseries and
100,000 samples show roughly a 13% decrease in total (VIRT) memory usage. In my
tests, this advantage for some reason decreased a bit the more samples the
timeseries had (to 5-7% for millions of samples). This I can't fully explain,
but perhaps garbage collection issues were involved.
*WHEN TO USE THE NEW TIMESTAMP TYPE*
The new clientmodel.Timestamp type should be used whenever time
calculations are either directly or indirectly related to sample
timestamps.
For example:
- the timestamp of a sample itself
- all kinds of watermarks
- anything that may become or is compared to a sample timestamp (like the timestamp
passed into Target.Scrape()).
When to still use time.Time:
- for measuring durations/times not related to sample timestamps, like duration
telemetry exporting, timers that indicate how frequently to execute some
action, etc.
*NOTE ON OPERATOR OPTIMIZATION TESTS*
We don't use operator optimization code anymore, but it still lives in
the code as dead code. It still has tests, but I couldn't get all of them to
pass with the new timestamp format. I commented out the failing cases for now,
but we should probably remove the dead code soon. I just didn't want to do that
in the same change as this.
Change-Id: I821787414b0debe85c9fffaeb57abd453727af0f
This fixes part 2) of https://github.com/prometheus/prometheus/issues/367
(uninitialized time.Time mapping to a higher LevelDB key than "normal"
timestamps).
Change-Id: Ib079974110a7b7c4757948f81fc47d3d29ae43c9
This fixes part 1) of https://github.com/prometheus/prometheus/issues/367 (the
storing of samples with the wrong fingerprint into a compacted chunk, thus
corrupting it).
Change-Id: I4c36d0d2e508e37a0aba90b8ca2ecc78ee03e3f1
This commit fixes a critique of the old storage API design, whereby
the input parameters were always as raw bytes and never Protocol
Buffer messages that encapsulated the data, meaning every place a
read or mutation was conducted needed to manually perform said
translations on its own. This is taxing.
Change-Id: I4786938d0d207cefb7782bd2bd96a517eead186f
While a hack, this change should allow us to serve queries
expeditiously during a flush operation.
Change-Id: I9a483fd1dd2b0638ab24ace960df08773c4a5079
The background curation should be staggered to ensure that disk
I/O yields to user-interactive operations in a timely manner. The
lack of routine prioritization necessitates this.
Change-Id: I9b498a74ccd933ffb856e06fedc167430e521d86
Move the stream to an interface, for a number of additional changes
around it are underway.
Conflicts:
storage/metric/memory.go
Change-Id: I4a5fc176f4a5274a64ebdb1cad52600954c463c3
AppendSample will be repcated with AppendSamples, which will take
advantage of bulks appends. This is a necessary step for indexing
pipeline decoupling.
Change-Id: Ia83811a87bcc89973d3b64d64b85a28710253ebc
This commit is the first of several and should not be regarded as the
desired end state for these cleanups. What this one does it, however,
is wrap the query index writing behind an interface type that can be
injected into the storage stack and have its lifecycle managed
separately as needed. It also would mean we can swap out underlying
implementations to support remote indexing, buffering, no-op indexing
very easily.
In the future, most of the individual index interface members in the
tiered storage will go away in favor of agents that can query and
resolve what they need from the datastore without the user knowing
how and why they work.
There are too many parameters to constructing a LevelDB storage
instance for a construction method, so I've opted to take an
idiomatic approach of embedding them in a struct for easier
mediation and versioning.
When samples get flushed to disk, they lose sub-second precision anyways. By
already dropping sub-second precision, data fetched from memory vs. disk will
behave the same. Later, we should consider also storing a more compact
representation than time.Time in memory if we're not going to use its full
precision.
Current series always get watermarks written out upon append now. This
drops support for old series without any watermarks by always reporting
them as too old (stale) during queries.
This also short-circuits optimize() for now, since it is complex to implement
for the new operator, and ops generated by the query layer already fulfill the
needed invariants. We should still investigate later whether to completely
delete operator optimization code or extend it to support
getValueRangeAtIntervalOp operators.
An design question was open for me in the beginning was whether to
serialize other types to disk, but Protocol Buffers quickly won out,
which allows us to drop support for other types. This is a good
start to cleaning up a lot of cruft in the storage stack and
can let us eventually decouple the various moving parts into
separate subsystems for easier reasoning.
This commit is not strictly required, but it is a start to making
the rest a lot more enjoyable to interact with.
This adds timers around several query-relevant code blocks. For now, the
query timer stats are only logged for queries initiated through the UI.
In other cases (rule evaluations), the stats are simply thrown away.
My hope is that this helps us understand where queries spend time,
especially in cases where they sometimes hang for unusual amounts of
time.
This commit conditionalizes the creation of the diskFrontier and
seriesFrontier along with the iterator such that they are provisioned
once something is actually required from disk.
This is mainly a small performance improvement, since we skip past the last
extracted time immediately if it was also the last sample in the chunk, instead
of trying to extract non-existent values before the chunk end again and again
and only gradually approaching the end of the chunk.
The current behavior only adds those samples to the view that are extracted by
the last pass of the last processed op and throws other ones away. This is a
bug. We need to append all samples that are extracted by each op pass.
This also makes view.appendSamples() take an array of samples.
The previous implementation spawned N goroutines to group samples
together and would not start work until the semaphore unblocked.
While this didn't leak, it polluted the scheduling space. Thusly,
the routine only starts after a semaphore has been acquired.
The one-off keys have been replaced with ``model.LabelPair``, which is
indexable. The performance impact is negligible, but it represents
a cognitive simplification.
The reality is that if we ever try to encode a Protocol Buffer and it
fails, it's likely that such an error is ultimately not a runtime error
and should be fixed forthwith. Thusly, we should rename
``Encoder.Encode`` to ``Encoder.MustEncode`` and drop the error return
value.
Some users of GetMetricForFingerprint() end up modifying the returned metric
labelset. Since the memory storage's implementation of
GetMetricForFingerprint() returned a pointer to the metric (and maps are
reference types anyways), the external mutation propagated back into the memory
storage.
The fix is to make a copy of the metric before returning it.
- only the data extracted in the last loop iteration of ExtractSamples() was
emitted as output
- if e.g. op interval < sample interval, there were situations where the same
sample was added multiple times to the output
This commit updates the documentation, Makefiles, formatting, and
code semantics to support the 1.1. runtime, which includes ...
1. ``make advice``,
2. ``make format``, and
3. ``go fix`` on various targets.
This commit simplifies the way that compactions across a database's
keyspace occur due to reading the LevelDB internals. Secondarily it
introduces the database size estimation mechanisms.
Include database health and help interfaces.
Add database statistics; remove status goroutines.
This commit kills the use of Go routines to expose status throughout
the web components of Prometheus. It also dumps raw LevelDB status
on a separate /databases endpoint.
This commit simplifies the way that compactions across a database's
keyspace occur due to reading the LevelDB internals. Secondarily it
introduces the database size estimation mechanisms.
This commit introduces the long-tail deletion mechanism, which will
automatically cull old sample values. It is an acceptable
hold-over until we get a resampling pipeline implemented.
Kill legacy OS X documentation, too.
This does two things:
1) Make TieredStorage.AppendSamples() write directly to memory instead of
buffering to a channel first. This is needed in cases where a rule might
immediately need the data generated by a previous rule.
2) Replace the single storage mutex by two new ones:
- memoryMutex - needs to be locked at any time that two concurrent
goroutines could be accessing (via read or write) the
TieredStorage memoryArena.
- memoryDeleteMutex - used to prevent any deletion of samples from
memoryArena as long as renderView is running and
assembling data from it.
The LevelDB disk storage does not need to be protected by a mutex when
rendering a view since renderView works off a LevelDB snapshot.
The rationale against adding memoryMutex directly to the memory storage: taking
a mutex does come with a small inherent time cost, and taking it is only
required in few places. In fact, no locking is required for the memory storage
instance which is part of a view (and not the TieredStorage).
This commit extracts the model.Values truncation behavior into the actual
tiered storage, which uses it and behaves in a peculiar way—notably the
retention of previous elements if the chunk were to ever go empty. This is
done to enable interpolation between sparse sample values in the evaluation
cycle. Nothing necessarily new here—just an extraction.
Now, the model.Values TruncateBefore functionality would do what a user
would expect without any surprises, which is required for the
DeletionProcessor, which may decide to split a large chunk in two if it
determines that the chunk contains the cut-off time.
This commit introduces three background compactors, which compact
sparse samples together.
1. Older than five minutes is grouped together into chunks of 50 every 30
minutes.
2. Older than 60 minutes is grouped together into chunks of 250 every 50
minutes.
3. Older than one day is grouped together into chunks of 5000 every 70
minutes.
This commit drops the Storage interface and just replaces it with a
publicized TieredStorage type. Storage had been anticipated to be
used as a wrapper for testability but just was not used due to
practicality. Merely overengineered. My bad. Anyway, we will
eventually instantiate the TieredStorage dependencies in main.go and
pass them in for more intelligent lifecycle management.
These changes will pave the way for managing the curators without
Law of Demeter violations.
This commit employs explicit memory freeing for the in-memory storage
arenas. Secondarily, we take advantage of smaller channel buffer sizes
in the test.
The curator requires the existence of a curator remark table, which
stores the progress for a given curation policy. The tests for the
curator create an ad hoc table, but core Prometheus presently lacks
said table, which this commit adds.
Secondarily, the error handling for the LevelDB lifecycle functions
in the metric persistence have been wrapped into an UncertaintyGroup,
which mirrors some of the functions of sync.WaitGroup but adds error
capturing capability to the mix.
This commit introduces to Prometheus a batch database sample curator,
which corroborates the high watermarks for sample series against the
curation watermark table to see whether a curator of a given type
needs to be run.
The curator is an abstract executor, which runs various curation
strategies across the database. It remarks the progress for each
type of curation processor that runs for a given sample series.
A curation procesor is responsible for effectuating the underlying
batch changes that are request. In this commit, we introduce the
CompactionProcessor, which takes several bits of runtime metadata and
combine sparse sample entries in the database together to form larger
groups. For instance, for a given series it would be possible to
have the curator effectuate the following grouping:
- Samples Older than Two Weeks: Grouped into Bunches of 10000
- Samples Older than One Week: Grouped into Bunches of 1000
- Samples Older than One Day: Grouped into Bunches of 100
- Samples Older than One Hour: Grouped into Bunches of 10
The benefits hereof of such a compaction are 1. a smaller search
space in the database keyspace, 2. better employment of compression
for repetious values, and 3. reduced seek times.
For the forthcoming Curator, we don't record timezone information in
the samples, nor do we in the curation remarks. All times are
recorded UTC. That said, for the test environment to better match
production, the special instant should be in UTC.
The curator work can be done easier if dto.SampleKey is no longer
directly accessed but rather has a higher level type around it that
captures a certain modicum of business logic. This doesn't look
terribly interesting today, but it will get more so.
After SampleValue was refactored into SampleValueSeries, which
involves plural values under a common super key, the stochastic
test was never refreshed to reflect this reality. We had other
tests that validated the functionality, but this one was
insufficently forward-ported.
This makes the memory persistence the backing store for views and
adjusts the MetricPersistence interface accordingly. It also removes
unused Get* method implementations from the LevelDB persistence so they
don't need to be adapted to the new interface. In the future, we should
rethink these interfaces.
All staleness and interpolation handling is now removed from the storage
layer and will be handled only by the query layer in the future.
The original append queue telemetry never worked, because it was
updated only upon the exit of the select statement, which would
usually liberate the queues of contents. This has been fixed to
be reported arbitrarily.
The queue sizes are now parameterizable via flags.
It is the case with the benchmark tool that we thought that we
generated multiple series and saved them to the disk as such, when
in reality, we overwrote the fields of the outgoing metrics via
Go map reference behavior. This was accidental. In the course of
diagnosing this, a few errors were found:
1. ``newSeriesFrontier`` should check to see if the candidate fingerprint is within the given domain of the ``diskFrontier``. If not, as the contract in the docstring stipulates, a ``nil`` ``seriesFrontier`` should be emitted.
2. In the interests of aiding debugging, the raw LevelDB ``levigoIterator`` type now includes a helpful forensics ``String()`` method.
This work produced additional cleanups:
1. ``Close() error`` with the storage stack is technically incorrect, since nowhere in the bowels of it does an error actually occur. The interface has been simplified to remove this for now.
After this commit, we'll need to add validations that it does the
desired work, which we presently know that it doesn't. Given the
changes I made with a plethora of renamings, I want to commit this
now before it gets even larger.
The curator doesn't do anything yet; rather, this is the type
definition including the anciliary testing scaffold.
Improve Makefile and Git developer experience.
The top-level Makefile was a bit overloaded in terms of generation of
assets and their management. This has been offloaded into separate
Makefiles.
The Git developer experience sucked due to lack of .gitignore
policies.
Also: Fix faulty skiplist naming from old merge.
The LevelDB storage types return an interface type now that wraps
around the underlying iterator. This both enhances testability but
improves upon, in my opinion, the interface design for the LevelDB
iterator.
Secondarily, the resource reaping behaviors for the LevelDB iterators
have been improved by dropping the externalized io.Closer object.
Finally, the iterator provisioning methods provide the option for
indicating whether one wants a snapshotted iterator or not.
EachFunc is deprecated.
Remove deprecated ``Pair`` and ``GetAll``.
These were originally used for forensic and the old gorest impl.
Nothing today in the user-facing path nor the tests uses them,
especially since the advent of the ForEach protocol in the
interface.
- Kill Close in Persistent and document interface.
- Extract batching behavior into interface.
- Kill IteratorManager, which was used for unknown reasons.
The LevelDB index retrievals could be repeated in a given operation
batch if multiple queued mutations affect the same (Label Name) singles
and (Label Name, Label Value) doubles. This is wasteful and
inefficient, as a single retrieval suffices. Thusly this commit
retrieves the canonical index mappings if the said mapping has not
been looked up in a given batch.
Snappy should have been explicitly included in the runtime, for I
erroneously thought that LevelDB bundled this into its runtime as-is.
It turns out that this assumption is wrong, and I thought we had
Snappy compression support all-along.
Presently our use of LevelDB and its operating modes are hardcoded
into the storage stack. This pull request decouples this and
re-exposes this through flags. We can now perform benchmarking
and remedial tuning.
client_golang was updated to support full label-oriented telemetry,
which introduced interface incompatibilities with the previous
version of Prometheus. To alleviate this, a general fetching and
processing dispatching system has been created, which discriminates
and processes according to the version of input.
This implementation needs to be cleaned up considerably, but it
should hopefully provide some breathing room. Ultimately this will
be extracted out of the storage layer---specifically the LevelDB
hierarchy---to interface with a generic set of abstractions for a
storage system, but this will be where it remains for now.
The LevelDB stochastic tests could take a long time.
Original:
```
Matt:prometheus mtp$ make test
make -C model
protoc --go_out=generated/ data.proto
go build ./...
go test ./...
warning: building out-of-date packages:
github.com/matttproud/golang_instrumentation/maths
github.com/matttproud/golang_instrumentation/utility
github.com/matttproud/golang_instrumentation/metrics
github.com/matttproud/golang_instrumentation
installing these packages with 'go test -i ./...' will speed future tests.
? github.com/matttproud/prometheus [no test files]
? github.com/matttproud/prometheus/coding [no test files]
ok github.com/matttproud/prometheus/coding/indexable 0.012s
? github.com/matttproud/prometheus/model [no test files]
? github.com/matttproud/prometheus/model/generated [no test files]
? github.com/matttproud/prometheus/retrieval [no test files]
? github.com/matttproud/prometheus/storage/metric [no test files]
ok github.com/matttproud/prometheus/storage/metric/leveldb 70.800s
? github.com/matttproud/prometheus/storage/raw [no test files]
? github.com/matttproud/prometheus/storage/raw/index [no test files]
ok github.com/matttproud/prometheus/storage/raw/index/leveldb 0.012s
ok github.com/matttproud/prometheus/storage/raw/leveldb 0.016s
ok github.com/matttproud/prometheus/utility 0.012s
? github.com/matttproud/prometheus/utility/test [no test files]
```
to
```
Matt:prometheus mtp$ make test
make -C model
protoc --go_out=generated/ data.proto
go build ./...
go test ./...
warning: building out-of-date packages:
github.com/matttproud/golang_instrumentation/maths
github.com/matttproud/golang_instrumentation/utility
github.com/matttproud/golang_instrumentation/metrics
github.com/matttproud/golang_instrumentation
installing these packages with 'go test -i ./...' will speed future tests.
? github.com/matttproud/prometheus [no test files]
? github.com/matttproud/prometheus/coding [no test files]
ok github.com/matttproud/prometheus/coding/indexable 0.011s
? github.com/matttproud/prometheus/model [no test files]
? github.com/matttproud/prometheus/model/generated [no test files]
? github.com/matttproud/prometheus/retrieval [no test files]
? github.com/matttproud/prometheus/storage/metric [no test files]
ok github.com/matttproud/prometheus/storage/metric/leveldb 2.158s
? github.com/matttproud/prometheus/storage/raw [no test files]
? github.com/matttproud/prometheus/storage/raw/index [no test files]
ok github.com/matttproud/prometheus/storage/raw/index/leveldb 0.013s
ok github.com/matttproud/prometheus/storage/raw/leveldb 0.013s
ok github.com/matttproud/prometheus/utility 0.013s
? github.com/matttproud/prometheus/utility/test [no test files]
```
Kill LevelDB watermarks due to redundancy.
General interface documentation has begun.
Creating custom types for the model to prevent errors down the
road.
Renaming of components for easier comprehension.
Exposition of interface in LevelDB.
Slew of simple refactorings.
