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.
Matt T. Proud