Use AppendableGauge to detect corrupt chunk with gauge histograms.
Detect if first sample is a gauge but the chunk is not set up to contain
gauge histograms.
Signed-off-by: György Krajcsovits <gyorgy.krajcsovits@grafana.com>
Signed-off-by: George Krajcsovits <krajorama@users.noreply.github.com>
We haven't updated golint-ci in our CI yet, but this commit prepares
for that.
There are a lot of new warnings, and it is mostly because the "revive"
linter got updated. I agree with most of the new warnings, mostly
around not naming unused function parameters (although it is justified
in some cases for documentation purposes – while things like mocks are
a good example where not naming the parameter is clearer).
I'm pretty upset about the "empty block" warning to include `for`
loops. It's such a common pattern to do something in the head of the
`for` loop and then have an empty block. There is still an open issue
about this: https://github.com/mgechev/revive/issues/810 I have
disabled "revive" altogether in files where empty blocks are used
excessively, and I have made the effort to add individual
`// nolint:revive` where empty blocks are used just once or twice.
It's borderline noisy, though, but let's go with it for now.
I should mention that none of the "empty block" warnings for `for`
loop bodies were legitimate.
Signed-off-by: beorn7 <beorn@grafana.com>
In the past, every sample value was a float, so it was fine to call a
variable holding such a float "value" or "sample". With native
histograms, a sample might have a histogram value. And a histogram
value is still a value. Calling a float value just "value" or "sample"
or "V" is therefore misleading. Over the last few commits, I already
renamed many variables, but this cleans up a few more places where the
changes are more invasive.
Note that we do not to attempt naming in the JSON APIs or in the
protobufs. That would be quite a disruption. However, internally, we
can call variables as we want, and we should go with the option of
avoiding misunderstandings.
Signed-off-by: beorn7 <beorn@grafana.com>
Instead of passing in a `ScratchBuilder` and `Labels`, just pass the
builder and the caller can extract labels from it. In many cases the
caller didn't use the Labels value anyway.
Now in `Labels.ScratchBuilder` we need a slightly different API: one
to assign what will be the result, instead of overwriting some other
`Labels`. This is safer and easier to reason about.
Signed-off-by: Bryan Boreham <bjboreham@gmail.com>
This necessitates a change to the `tsdb.IndexReader` interface:
`index.Reader` is used from multiple goroutines concurrently, so we
can't have state in it.
We do retain a `ScratchBuilder` in `blockBaseSeriesSet` which is
iterator-like.
Signed-off-by: Bryan Boreham <bjboreham@gmail.com>
Use simpler utility function to create Labels objects, making fewer
assumptions about the data structure.
Signed-off-by: Bryan Boreham <bjboreham@gmail.com>
Re-use previous memory if it is already of the correct type.
Also turn two levels of function closure into a single object that
holds the required data.
Signed-off-by: Bryan Boreham <bjboreham@gmail.com>
Patterned after `Chunk.Iterator()`: pass the old iterator in so it
can be re-used to avoid allocating a new object.
(This commit does not do any re-use; it is just changing all the method
signatures so re-use is possible in later commits.)
Signed-off-by: Bryan Boreham <bjboreham@gmail.com>
* Introduce out-of-order TSDB support
This implementation is based on this design doc:
https://docs.google.com/document/d/1Kppm7qL9C-BJB1j6yb6-9ObG3AbdZnFUBYPNNWwDBYM/edit?usp=sharing
This commit adds support to accept out-of-order ("OOO") sample into the TSDB
up to a configurable time allowance. If OOO is enabled, overlapping querying
are automatically enabled.
Most of the additions have been borrowed from
https://github.com/grafana/mimir-prometheus/
Here is the list ist of the original commits cherry picked
from mimir-prometheus into this branch:
- 4b2198d7ec
- 2836e5513f
- 00b379c3a5
- ff0dc75758
- a632c73352
- c6f3d4ab33
- 5e8406a1d4
- abde1e0ba1
- e70e769889
- df59320886
Co-authored-by: Jesus Vazquez <jesus.vazquez@grafana.com>
Co-authored-by: Ganesh Vernekar <ganeshvern@gmail.com>
Co-authored-by: Dieter Plaetinck <dieter@grafana.com>
Signed-off-by: Jesus Vazquez <jesus.vazquez@grafana.com>
* gofumpt files
Signed-off-by: Jesus Vazquez <jesus.vazquez@grafana.com>
* Add license header to missing files
Signed-off-by: Jesus Vazquez <jesus.vazquez@grafana.com>
* Fix OOO tests due to existing chunk disk mapper implementation
Signed-off-by: Jesus Vazquez <jesus.vazquez@grafana.com>
* Fix truncate int overflow
Signed-off-by: Jesus Vazquez <jesus.vazquez@grafana.com>
* Add Sync method to the WAL and update tests
Signed-off-by: Jesus Vazquez <jesus.vazquez@grafana.com>
* remove useless sync
Signed-off-by: Jesus Vazquez <jesus.vazquez@grafana.com>
* Update minOOOTime after truncating Head
* Update minOOOTime after truncating Head
Signed-off-by: Ganesh Vernekar <ganeshvern@gmail.com>
* Fix lint
Signed-off-by: Ganesh Vernekar <ganeshvern@gmail.com>
* Add a unit test
Signed-off-by: Ganesh Vernekar <ganeshvern@gmail.com>
Signed-off-by: Jesus Vazquez <jesus.vazquez@grafana.com>
* Load OutOfOrderTimeWindow only once per appender
Signed-off-by: Jesus Vazquez <jesus.vazquez@grafana.com>
* Fix OOO Head LabelValues and PostingsForMatchers
Signed-off-by: Jesus Vazquez <jesus.vazquez@grafana.com>
* Fix replay of OOO mmap chunks
Signed-off-by: Ganesh Vernekar <ganeshvern@gmail.com>
* Remove unnecessary err check
Signed-off-by: Jesus Vazquez <jesus.vazquez@grafana.com>
* Prevent panic with ApplyConfig
Signed-off-by: Ganesh Vernekar 15064823+codesome@users.noreply.github.com
Signed-off-by: Jesus Vazquez <jesus.vazquez@grafana.com>
* Run OOO compaction after restart if there is OOO data from WBL
Signed-off-by: Ganesh Vernekar 15064823+codesome@users.noreply.github.com
Signed-off-by: Jesus Vazquez <jesus.vazquez@grafana.com>
* Apply Bartek's suggestions
Co-authored-by: Bartlomiej Plotka <bwplotka@gmail.com>
Signed-off-by: Jesus Vazquez <jesus.vazquez@grafana.com>
* Refactor OOO compaction
Signed-off-by: Ganesh Vernekar <ganeshvern@gmail.com>
* Address comments and TODOs
- Added a comment explaining why we need the allow overlapping
compaction toggle
- Clarified TSDBConfig OutOfOrderTimeWindow doc
- Added an owner to all the TODOs in the code
Signed-off-by: Jesus Vazquez <jesus.vazquez@grafana.com>
* Run go format
Signed-off-by: Jesus Vazquez <jesus.vazquez@grafana.com>
* Fix remaining review comments
Signed-off-by: Ganesh Vernekar <ganeshvern@gmail.com>
* Fix tests
Signed-off-by: Ganesh Vernekar <ganeshvern@gmail.com>
* Change wbl reference when truncating ooo in TestHeadMinOOOTimeUpdate
Signed-off-by: Jesus Vazquez <jesus.vazquez@grafana.com>
* Fix TestWBLAndMmapReplay test failure on windows
Signed-off-by: Ganesh Vernekar <ganeshvern@gmail.com>
* Address most of the feedback
Signed-off-by: Ganesh Vernekar <ganeshvern@gmail.com>
* Refactor the block meta for out of order
Signed-off-by: Ganesh Vernekar <ganeshvern@gmail.com>
* Fix windows error
Signed-off-by: Ganesh Vernekar <ganeshvern@gmail.com>
* Fix review comments
Signed-off-by: Ganesh Vernekar <ganeshvern@gmail.com>
Signed-off-by: Jesus Vazquez <jesus.vazquez@grafana.com>
Signed-off-by: Ganesh Vernekar <ganeshvern@gmail.com>
Signed-off-by: Ganesh Vernekar 15064823+codesome@users.noreply.github.com
Co-authored-by: Ganesh Vernekar <15064823+codesome@users.noreply.github.com>
Co-authored-by: Ganesh Vernekar <ganeshvern@gmail.com>
Co-authored-by: Dieter Plaetinck <dieter@grafana.com>
Co-authored-by: Oleg Zaytsev <mail@olegzaytsev.com>
Co-authored-by: Bartlomiej Plotka <bwplotka@gmail.com>
- Pick At... method via return value of Next/Seek.
- Do not clobber returned buckets.
- Add partial FloatHistogram suppert.
Note that the promql package is now _only_ dealing with
FloatHistograms, following the idea that PromQL only knows float
values.
As a byproduct, I have removed the histogramSeries metric. In my
understanding, series can have both float and histogram samples, so
that metric doesn't make sense anymore.
As another byproduct, I have converged the sampleBuf and the
histogramSampleBuf in memSeries into one. The sample type stored in
the sampleBuf has been extended to also contain histograms even before
this commit.
Signed-off-by: beorn7 <beorn@grafana.com>
This is to avoid copying the many fields of a histogram.Histogram all
the time.
This also fixes a bunch of formerly broken tests.
Signed-off-by: beorn7 <beorn@grafana.com>
This creates a new `model` directory and moves all data-model related
packages over there:
exemplar labels relabel rulefmt textparse timestamp value
All the others are more or less utilities and have been moved to `util`:
gate logging modetimevfs pool runtime
Signed-off-by: beorn7 <beorn@grafana.com>
* TSDB: demistify seriesRefs and ChunkRefs
The TSDB package contains many types of series and chunk references,
all shrouded in uint types. Often the same uint value may
actually mean one of different types, in non-obvious ways.
This PR aims to clarify the code and help navigating to relevant docs,
usage, etc much quicker.
Concretely:
* Use appropriately named types and document their semantics and
relations.
* Make multiplexing and demuxing of types explicit
(on the boundaries between concrete implementations and generic
interfaces).
* Casting between different types should be free. None of the changes
should have any impact on how the code runs.
TODO: Implement BlockSeriesRef where appropriate (for a future PR)
Signed-off-by: Dieter Plaetinck <dieter@grafana.com>
* feedback
Signed-off-by: Dieter Plaetinck <dieter@grafana.com>
* agent: demistify seriesRefs and ChunkRefs
Signed-off-by: Dieter Plaetinck <dieter@grafana.com>
* Allow to disable trimming when querying TSDB
Signed-off-by: Marco Pracucci <marco@pracucci.com>
* Addressed review comments
Signed-off-by: Marco Pracucci <marco@pracucci.com>
* Added unit test
Signed-off-by: Marco Pracucci <marco@pracucci.com>
* Renamed TrimDisabled to DisableTrimming
Signed-off-by: Marco Pracucci <marco@pracucci.com>
* Push the matchers for LabelNames all the way into the index.
NB This doesn't actually implement it in the index, just plumbs it through for now...
Signed-off-by: Tom Wilkie <tom@grafana.com>
* Hack it up. Does not work.
Signed-off-by: Tom Wilkie <tom@grafana.com>
* Revert changes I don't understand
Can't see why do we need to hold a mutex on symbols, and the purpose of
the LabelNamesFor method.
Maybe I'll need to re-add this later.
Signed-off-by: Oleg Zaytsev <mail@olegzaytsev.com>
* Implement LabelNamesFor
This method provides the label names that appear in the postings
provided. We do that deeper than the label values because we know
beforehand that most of the label names we'll be the same across
different postings, and we don't want to go down an up looking up the
same symbols for all different series.
Signed-off-by: Oleg Zaytsev <mail@olegzaytsev.com>
* Mutex on symbols should be unlocked
However, I still don't understand why do we need a mutex here.
Signed-off-by: Oleg Zaytsev <mail@olegzaytsev.com>
* Fix head.LabelNamesFor
Signed-off-by: Oleg Zaytsev <mail@olegzaytsev.com>
* Implement mockIndex LabelNames with matchers
Signed-off-by: Oleg Zaytsev <mail@olegzaytsev.com>
* Nitpick on slice initialisation
Signed-off-by: Oleg Zaytsev <mail@olegzaytsev.com>
* Add tests for LabelNamesWithMatchers
Signed-off-by: Oleg Zaytsev <mail@olegzaytsev.com>
* Fix the mutex mess on head.LabelValues/LabelNames
I still don't see why we need to grab that unrelated mutex, but at least
now we're grabbing it consistently
Signed-off-by: Oleg Zaytsev <mail@olegzaytsev.com>
* Check error after iterating postings
Signed-off-by: Oleg Zaytsev <mail@olegzaytsev.com>
* Use the error from posting when there was en error in postings
Co-authored-by: Ganesh Vernekar <15064823+codesome@users.noreply.github.com>
Signed-off-by: Oleg Zaytsev <mail@olegzaytsev.com>
* Update storage/interface.go comment
Signed-off-by: Oleg Zaytsev <mail@olegzaytsev.com>
Co-authored-by: Ganesh Vernekar <15064823+codesome@users.noreply.github.com>
* Update tsdb/index/index.go comment
Signed-off-by: Oleg Zaytsev <mail@olegzaytsev.com>
Co-authored-by: Ganesh Vernekar <15064823+codesome@users.noreply.github.com>
* Update tsdb/index/index.go wrapped error msg
Signed-off-by: Oleg Zaytsev <mail@olegzaytsev.com>
Co-authored-by: Ganesh Vernekar <15064823+codesome@users.noreply.github.com>
* Update tsdb/index/index.go wrapped error msg
Signed-off-by: Oleg Zaytsev <mail@olegzaytsev.com>
Co-authored-by: Ganesh Vernekar <15064823+codesome@users.noreply.github.com>
* Update tsdb/index/index.go warpped error msg
Signed-off-by: Oleg Zaytsev <mail@olegzaytsev.com>
Co-authored-by: Ganesh Vernekar <15064823+codesome@users.noreply.github.com>
* Remove unneeded comment
Signed-off-by: Oleg Zaytsev <mail@olegzaytsev.com>
* Add testcases for LabelNames w/matchers in api.go
Signed-off-by: Oleg Zaytsev <mail@olegzaytsev.com>
* Use t.Cleanup() instead of defer in tests
Signed-off-by: Oleg Zaytsev <mail@olegzaytsev.com>
Co-authored-by: Tom Wilkie <tom@grafana.com>
Co-authored-by: Ganesh Vernekar <15064823+codesome@users.noreply.github.com>
* Added walreplay API endpoint
Signed-off-by: Levi Harrison <git@leviharrison.dev>
* Added starting page to react-ui
Signed-off-by: Levi Harrison <git@leviharrison.dev>
* Documented the new endpoint
Signed-off-by: Levi Harrison <git@leviharrison.dev>
* Fixed typos
Signed-off-by: Levi Harrison <git@leviharrison.dev>
Co-authored-by: Julius Volz <julius.volz@gmail.com>
* Removed logo
Signed-off-by: Levi Harrison <git@leviharrison.dev>
* Changed isResponding to isUnexpected
Signed-off-by: Levi Harrison <git@leviharrison.dev>
* Changed width of progress bar
Signed-off-by: Levi Harrison <git@leviharrison.dev>
* Changed width of progress bar
Signed-off-by: Levi Harrison <git@leviharrison.dev>
* Added DB stats object
Signed-off-by: Levi Harrison <git@leviharrison.dev>
* Updated starting page to work with new fields
Signed-off-by: Levi Harrison <git@leviharrison.dev>
* Passing nil
Signed-off-by: Levi Harrison <git@leviharrison.dev>
* Passing nil (pt. 2)
Signed-off-by: Levi Harrison <git@leviharrison.dev>
* Passing nil (pt. 3)
Signed-off-by: Levi Harrison <git@leviharrison.dev>
* Passing nil (and also implementing a method this time) (pt. 4)
Signed-off-by: Levi Harrison <git@leviharrison.dev>
* Passing nil (and also implementing a method this time) (pt. 5)
Signed-off-by: Levi Harrison <git@leviharrison.dev>
* Changed const to let
Signed-off-by: Levi Harrison <git@leviharrison.dev>
* Passing nil (pt. 6)
Signed-off-by: Levi Harrison <git@leviharrison.dev>
* Remove SetStats method
Signed-off-by: Levi Harrison <git@leviharrison.dev>
* Added comma
Signed-off-by: Levi Harrison <git@leviharrison.dev>
* Changed api
Signed-off-by: Levi Harrison <git@leviharrison.dev>
* Changed to triple equals
Signed-off-by: Levi Harrison <git@leviharrison.dev>
* Fixed data response types
Signed-off-by: Levi Harrison <git@leviharrison.dev>
* Don't return pointer
Signed-off-by: Levi Harrison <git@leviharrison.dev>
* Changed version
Signed-off-by: Levi Harrison <git@leviharrison.dev>
* Fixed interface issue
Signed-off-by: Levi Harrison <git@leviharrison.dev>
* Fixed pointer
Signed-off-by: Levi Harrison <git@leviharrison.dev>
* Fixed copying lock value error
Signed-off-by: Levi Harrison <git@leviharrison.dev>
Co-authored-by: Julius Volz <julius.volz@gmail.com>
It's common to see queries like bar=~"foo" from machine generated
queries in the fronted. These are not evaluated as regexps, but are a
single-value-set, i.e. and equality matchings instead.
This is just a testcase for a single-value case.
Signed-off-by: Oleg Zaytsev <mail@olegzaytsev.com>
This moves the label lookup into TSDB, whilst still keeping the cached-ref optimisation for repeated Appends.
This makes the API easier to consume and implement. In particular this change is motivated by the scrape-time-aggregation work, which I don't think is possible to implement without it as it needs access to label values.
Signed-off-by: Tom Wilkie <tom.wilkie@gmail.com>
* Testify: move to require
Moving testify to require to fail tests early in case of errors.
Signed-off-by: Julien Pivotto <roidelapluie@inuits.eu>
* More moves
Signed-off-by: Julien Pivotto <roidelapluie@inuits.eu>
* Refactor test assertions
This pull request gets rid of assert.True where possible to use
fine-grained assertions.
Signed-off-by: Julien Pivotto <roidelapluie@inuits.eu>
I did not want to move those in previous PR to make it easier to review. Now small cleanup time for readability. (:
## Changes
* Merge series goes to `storage/merge.go` leaving `fanout.go` for just fanout code.
* Moved `fanout test` code from weird separate package to storage.
* Unskiped one test: TestFanout_SelectSorted/chunk_querier
* Moved block series set codes responsible for querying blocks to `querier.go` from `compact.go`
Signed-off-by: Bartlomiej Plotka <bwplotka@gmail.com>
* tsdb: Added ChunkQueryable implementations to db; unified compactor, querier and fanout block iterating.
Chained to https://github.com/prometheus/prometheus/pull/7059
* NewMerge(Chunk)Querier now takies multiple primaries allowing tsdb DB code to use it.
* Added single SeriesEntry / ChunkEntry for all series implementations.
* Unified all vertical, and non vertical for compact and querying to single
merge series / chunk sets by reusing VerticalSeriesMergeFunc for overlapping algorithm (same logic as before)
* Added block (Base/Chunk/)Querier for block querying. We then use populateAndTomb(Base/Chunk/) to iterate over chunks or samples.
* Refactored endpoint tests and querier tests to include subtests.
Signed-off-by: Bartlomiej Plotka <bwplotka@gmail.com>
* Addressed comments from Brian and Beorn.
Signed-off-by: Bartlomiej Plotka <bwplotka@gmail.com>
* Fixed snapshot test and added chunk iterator support for DBReadOnly.
Signed-off-by: Bartlomiej Plotka <bwplotka@gmail.com>
* Fixed race when iterating over Ats first.
Signed-off-by: Bartlomiej Plotka <bwplotka@gmail.com>
* Fixed tests.
Signed-off-by: Bartlomiej Plotka <bwplotka@gmail.com>
* Fixed populate block tests.
Signed-off-by: Bartlomiej Plotka <bwplotka@gmail.com>
* Fixed endpoints test.
Signed-off-by: Bartlomiej Plotka <bwplotka@gmail.com>
* Fixed test.
Signed-off-by: Bartlomiej Plotka <bwplotka@gmail.com>
* Added test & fixed case of head open chunk.
Signed-off-by: Bartlomiej Plotka <bwplotka@gmail.com>
* Fixed DBReadOnly tests and bug producing 1 sample chunks.
Signed-off-by: Bartlomiej Plotka <bwplotka@gmail.com>
* Added cases for partial block overlap for multiple full chunks.
Signed-off-by: Bartlomiej Plotka <bwplotka@gmail.com>
* Added extra tests for chunk meta after compaction.
Signed-off-by: Bartlomiej Plotka <bwplotka@gmail.com>
* Fixed small vertical merge bug and added more tests for that.
Signed-off-by: Bartlomiej Plotka <bwplotka@gmail.com>
* Add errors and Warnings to SeriesSet
Signed-off-by: Kemal Akkoyun <kakkoyun@gmail.com>
* Change Querier interface and refactor accordingly
Signed-off-by: Kemal Akkoyun <kakkoyun@gmail.com>
* Refactor promql/engine to propagate warnings at eval stage
Signed-off-by: Kemal Akkoyun <kakkoyun@gmail.com>
* Address review issues
Signed-off-by: Kemal Akkoyun <kakkoyun@gmail.com>
* Make sure all the series from all Selects are pre-advanced
Signed-off-by: Kemal Akkoyun <kakkoyun@gmail.com>
* Address review issues
Signed-off-by: Kemal Akkoyun <kakkoyun@gmail.com>
* Separate merge series sets
Signed-off-by: Kemal Akkoyun <kakkoyun@gmail.com>
* Clean
Signed-off-by: Kemal Akkoyun <kakkoyun@gmail.com>
* Refactor merge querier failure handling
Signed-off-by: Kemal Akkoyun <kakkoyun@gmail.com>
* Refactored and simplified fanout with improvements from incoming chunk iterator PRs.
* Secondary logic is hidden, instead of weird failed series set logic we had.
* Fanout is well commented
* Fanout closing record all errors
* MergeQuerier improved API (clearer)
* deferredGenericMergeSeriesSet is not needed as we return no samples anyway for failed series sets (next = false).
Signed-off-by: Bartlomiej Plotka <bwplotka@gmail.com>
* Fix formatting
Signed-off-by: Kemal Akkoyun <kakkoyun@gmail.com>
* Fix CI issues
Signed-off-by: Kemal Akkoyun <kakkoyun@gmail.com>
* Added final tests for error handling.
Signed-off-by: Bartlomiej Plotka <bwplotka@gmail.com>
* Addressed Brian's comments.
* Moved hints in populate to be allocated only when needed.
* Used sync.Once in secondary Querier to achieve all-or-nothing partial response logic.
* Select after first Next is done will panic.
NOTE: in lazySeriesSet in theory we could just panic, I think however we can
totally just return error, it will panic in expand anyway.
Signed-off-by: Bartlomiej Plotka <bwplotka@gmail.com>
* Utilize errWithWarnings
Signed-off-by: Kemal Akkoyun <kakkoyun@gmail.com>
* Fix recently introduced expansion issue
Signed-off-by: Kemal Akkoyun <kakkoyun@gmail.com>
* Add tests for secondary querier error handling
Signed-off-by: Kemal Akkoyun <kakkoyun@gmail.com>
* Implement lazy merge
Signed-off-by: Kemal Akkoyun <kakkoyun@gmail.com>
* Add name to test cases
Signed-off-by: Kemal Akkoyun <kakkoyun@gmail.com>
* Reorganize
Signed-off-by: Kemal Akkoyun <kakkoyun@gmail.com>
* Address review comments
Signed-off-by: Kemal Akkoyun <kakkoyun@gmail.com>
* Address review comments
Signed-off-by: Kemal Akkoyun <kakkoyun@gmail.com>
* Remove redundant warnings
Signed-off-by: Kemal Akkoyun <kakkoyun@gmail.com>
* Fix rebase mistake
Signed-off-by: Kemal Akkoyun <kakkoyun@gmail.com>
Co-authored-by: Bartlomiej Plotka <bwplotka@gmail.com>
* Callbacks for lifecycle of series in TSDB
Signed-off-by: Ganesh Vernekar <cs15btech11018@iith.ac.in>
* Add more comments
Signed-off-by: Ganesh Vernekar <cs15btech11018@iith.ac.in>
When appending to the head and a chunk is full it is flushed to the disk and m-mapped (memory mapped) to free up memory
Prom startup now happens in these stages
- Iterate the m-maped chunks from disk and keep a map of series reference to its slice of mmapped chunks.
- Iterate the WAL as usual. Whenever we create a new series, look for it's mmapped chunks in the map created before and add it to that series.
If a head chunk is corrupted the currpted one and all chunks after that are deleted and the data after the corruption is recovered from the existing WAL which means that a corruption in m-mapped files results in NO data loss.
[Mmaped chunks format](https://github.com/prometheus/prometheus/blob/master/tsdb/docs/format/head_chunks.md) - main difference is that the chunk for mmaping now also includes series reference because there is no index for mapping series to chunks.
[The block chunks](https://github.com/prometheus/prometheus/blob/master/tsdb/docs/format/chunks.md) are accessed from the index which includes the offsets for the chunks in the chunks file - example - chunks of series ID have offsets 200, 500 etc in the chunk files.
In case of mmaped chunks, the offsets are stored in memory and accessed from that. During WAL replay, these offsets are restored by iterating all m-mapped chunks as stated above by matching the series id present in the chunk header and offset of that chunk in that file.
**Prombench results**
_WAL Replay_
1h Wal reply time
30% less wal reply time - 4m31 vs 3m36
2h Wal reply time
20% less wal reply time - 8m16 vs 7m
_Memory During WAL Replay_
High Churn:
10-15% less RAM - 32gb vs 28gb
20% less RAM after compaction 34gb vs 27gb
No Churn:
20-30% less RAM - 23gb vs 18gb
40% less RAM after compaction 32.5gb vs 20gb
Screenshots are in [this comment](https://github.com/prometheus/prometheus/pull/6679#issuecomment-621678932)
Signed-off-by: Ganesh Vernekar <cs15btech11018@iith.ac.in>
