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
MIN/MAX/SUM/AVG/COUNT aggregations will now by default drop all labels that are
not specifically part of a BY-clause, even if a label value is the same within
all timeseries of an aggregation group. The old behavior of keeping extra
labels may still be switched on by adding KEEPING_EXTRA to the end of an
aggregation statement:
sum(http_requests) by (job, method) keeping_extra
I'm open to better syntax/naming suggestions.
Change-Id: I21d3fe7af9e98552ce3dffa3ce7c0a4ba4c0b4a4
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 adds search domain support by trying to resolve a name by
appending each search domain configured in /etc/resolv.conf until
the query succeeds (NOERROR) and has at least one answer.
Change-Id: Ibdc5138c5d8cc049e11fab90c3d5243d5a06852c
* changes:
fix link to CONTRIBUTING.md in README.md
moved CONTRIBUTING.md to top of repo; link to CONTRIBUTING.md in README.md
change double quotes to backticks for md awesomeness
add contributing.md
Due to on going issues, we've decided to remove gorest. It started with gorest
not being thread-safe (it does introspection to create a new handler which is
an easy process to mess up with multiple threads of execution):
https://code.google.com/p/gorest/issues/detail?id=15
While the issue has been marked fixed, it looks like the patch has introduced
more problems than the original issue and simply doesn't work properly.
I'm not sure the behaviour was thought through properly. If a new instance is
needed every request then a handler-factory is needed or the library needs to
set expectations about how the new objects should interact with their
constructor state.
While it was tempting to try out another routing library, I think for now
it's better to use dumb vanilla Go routing. At least until we decide which
URL format we intend to standardize on.
Change-Id: Ica3da135d05f8ab8fc206f51eeca4f684f8efa0e
- Modified sample conf so it is useable by default, also added some
comments from the 'hello world' configuration.
- Updated README so there's a clear two step start for newbies.
- Added extra vim swap files to gitignore.
Change-Id: I76203973db4a7b332014662fcfb2ce5e7d137bd8
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
