This simplifies the cache.Snapshot func to swap the hot cache to
the snapshot cache instead of copy and appending entries. This
reduces the amount of time the cache is write locked which should
reduce cache contention for the read only code paths.
Currently, whenever a snapshot occurs the Cache is reset and so many
allocations are repeated, as the same type of data is re-added to
the Cache.
This commit allows the stores to keep track of the number of values
within an entry, and use that size as a hint when the same entry needs
to be recreated after a snapshot.
To avoid hints persisting over a long period of time they are deleting
after every snapshot, and rebuilt using the most recent entries only.
When a limit is exceeded, we return errors and sometimes log (if appropriate)
that a limit was exceeded. The messages don't always provide an indication
as to where or how they are configured.
Instead, return the config option (easily searchable for) as well as the limit
currently set and the value that exceeded it when possible.
If concurrent writes to the same shard occur, it's possible for different types to
be added to the cache for the same series. The way the measurementFields map on the
shard is updated is racy in this scenario which would normally prevent this from occurring.
When this occurs, the snapshot compaction panics because it can't encode different types
in the same series.
To prevent this, we have the cache return an error a different type is added to existing
values in the cache.
Fixes#7498
Reduce the cache lock contention by widening the cache lock scope in WriteMulti, while this sounds counter intuitive it was:
* 1 x Read Lock to read the size
* 1 x Read Lock per values
* 1 x Write Lock per values on race
* 1 x Write Lock to update the size
We now have:
* 1 x Write Lock
This also reduces contention on the entries Values lock too as we have the global cache lock.
Move the calculation of the added size before taking the lock as it takes time and doesn't need the lock.
This also fixes a race in WriteMulti due to the lock not being held across the entire operation, which could cause the cache size to have an invalid value if Snapshot has been run in the between the addition of the values and the size update.
Fix the cache benchmark which where benchmarking the creation of the cache not its operation and add a parallel test for more real world scenario, however this could still be improved.
Add a fast path newEntryValues values for the new case which avoids taking the values lock and all the other calculations.
Drop the lock before performing the sort in Cache.Keys().
If cache.Deduplicate is called while writes are in-flight on the cache, a data race
could occur.
WARNING: DATA RACE
Write by goroutine 15:
runtime.mapassign1()
/usr/local/go/src/runtime/hashmap.go:429 +0x0
github.com/influxdata/influxdb/tsdb/engine/tsm1.(*Cache).entry()
/Users/jason/go/src/github.com/influxdata/influxdb/tsdb/engine/tsm1/cache.go:482 +0x27e
github.com/influxdata/influxdb/tsdb/engine/tsm1.(*Cache).WriteMulti()
/Users/jason/go/src/github.com/influxdata/influxdb/tsdb/engine/tsm1/cache.go:207 +0x3b2
github.com/influxdata/influxdb/tsdb/engine/tsm1.TestCache_Deduplicate_Concurrent.func1()
/Users/jason/go/src/github.com/influxdata/influxdb/tsdb/engine/tsm1/cache_test.go:421 +0x73
Previous read by goroutine 16:
runtime.mapiterinit()
/usr/local/go/src/runtime/hashmap.go:607 +0x0
github.com/influxdata/influxdb/tsdb/engine/tsm1.(*Cache).Deduplicate()
/Users/jason/go/src/github.com/influxdata/influxdb/tsdb/engine/tsm1/cache.go:272 +0x7c
github.com/influxdata/influxdb/tsdb/engine/tsm1.TestCache_Deduplicate_Concurrent.func2()
/Users/jason/go/src/github.com/influxdata/influxdb/tsdb/engine/tsm1/cache_test.go:429 +0x69
Goroutine 15 (running) created at:
github.com/influxdata/influxdb/tsdb/engine/tsm1.TestCache_Deduplicate_Concurrent()
/Users/jason/go/src/github.com/influxdata/influxdb/tsdb/engine/tsm1/cache_test.go:423 +0x3f2
testing.tRunner()
/usr/local/go/src/testing/testing.go:473 +0xdc
Goroutine 16 (finished) created at:
github.com/influxdata/influxdb/tsdb/engine/tsm1.TestCache_Deduplicate_Concurrent()
/Users/jason/go/src/github.com/influxdata/influxdb/tsdb/engine/tsm1/cache_test.go:431 +0x43b
testing.tRunner()
/usr/local/go/src/testing/testing.go:473 +0xdc
A deadlock occurs under write load if a backup is run in between the
time when a snapshot compactions has snapshotted the cache and successfully
written it to disk. The issus is that the second snapshot call will block
on the commit lock while it is holding the engine write lock. This causes
all writes to block as well as prevents the currently runnign snapshot
compaction from completing because it needs to acquire a read-lock.
This PR removes the commit lock and just returns an error if a snapshot is
in progress to all any locks being held to be released. The caller can determine
whether to retry or giveup.
Consider the write sequence: 6,1,snapshot,7,2.
The hot cache gets deduplicated, so is 2,7.
Now consider the test if 1 >= 2, this is false, so needSort is not set to true.
The problem is the implicit assumption that the snapshot is always sorted
by the time that merged() runs, but this may not be true.
Signed-off-by: Jon Seymour <jon@wildducktheories.com>
Currently two compactors can execute Engine.WriteSnapshot at once.
This isn't thread safe since both threads want to make modifications to
Cache.snapshot at the same time.
This commit introduces a lock which is acquired during Snapshot() and
released during ClearSnapshot(), ensuring that at most one thread
executes within Engine.WriteSnapshot() at once.
To ensure that we always release this lock, but only release the
snapshot resources on a successful commit, we modify ClearSnapshot() to
accept a boolean which indicates whether the write was successful or not
and guarantee to call this function if Snapshot() has been called.
Signed-off-by: Jon Seymour <jon@wildducktheories.com>
The Cache had support for taking multiple snapshots to support writing
multiple snapshots to TSM files concurrently if that happened to be
a bottleneck. In practice, this is never a bottleneck and we only
run one snappshoting goroutine continously per shard which has worked
well for all workloads.
The multiple snapshot support introduces some unhandled failure scenarios
where wal segments could be removed without writing them to TSM files. If
a snapshot compaction fails to write due to transient disk errors, subsequent
snapshots will continue, but the failed one will not be retried. When the
subsequent ones succeeded, all closed wal segments are removed causing data
loss.
This change simplifies the snapshotting capability to ensure that there is only
ever one snapshot. If one fails, the next snapshot will update the existing
snapshot and retry all of old and new data.
Fixes#5686
The cache had some incorrect logic for determine when a series needed
to be deduplicated. The logic was checking for unsorted points and
not considering duplicate points. This would manifest itself as many
points (duplicate) points being returned from the cache and after a
snapshot compaction run, the points would disappear because snapshot
compaction always deduplicates and sorts the points.
Added a test that reproduces the issue.
Fixes#5719
The test to see if the destination buffer for encoding and decoding a WAL
entry was broken and would cause a panic if there were large batches that
would overflow the buffer size.
Fixes#5075
* remove rolloverTSMFileSize constant that is no longer used
* remove the maxGenerationFileCount since it is no longer a limitation that's necessary with the new compaction scheme. We no longer read WAL segments as part of the compaction so memory is only used as we read in each individual key
* remove minFileCount and switch to a user configurable variable
* remove the mutex from WALSegmentWriter. There's never more than one open in the WAL at one time and it's not exported through any function so the lock on the WAL should be used. This simplified keeping track of the last write time and removed a bunch of unnecessary locks.
* update WALSegmentWriter.Write to take the compressed bytes so that encoding and compression can occur before the call to write (while we don't hold the WAL lock)
* remove a bunch of unnecessary locking in WAL.writeToLog
* Add check for TSM file magic number and vesion
* Remove old tsm, log, and unused cursor code
* Remove references to tsm1dev everywhere except in the inspector
* Clean up config options for compaction and snapshotting
* Remove old TSM configuration options
* Update the config.sample.toml with TSM options
* Update WAL compact to force if it has been cold for writes for a configurable period of time (1h by default)
This change starts by building the sequence of entries, which also
allows the required size of destination buffer to be calculated. Then
the buffer is allocated up-front in 1 call.
Each snapshot and hot value-set is appended to the buffer. If ordering
is violated at anytime, set the 'needSort' flag. Sorting, if necessary,
is performed just before returning the data.
* Update cache to have a single slice of values for a key (removed checkpoints)
* Changed compact.Plan to only worry about TSM files.
* Updated Plan to not return an error since there was no case in which it would.
* Update WAL to not keep stats since they're no longer needed.
* Update engine to flush the Cache/WAL to a new TSM file when the min threshold is hit.
* Split compact logic between TSM compacts and WAL/Cache writes.
* Remove unnecessary merge iterator, wal segment iterator, and other no longer necessary stuff.
* Remove the asending bool from the Dedupe method. Values should always be in ascending order. It's up to the cursor to iterate through values based on the direction. Giving the cursor responsibility makes it so we don't need to sort, dedupe or reallocate anything for different query orders.
* Updated engine to use its locks to ensure writes and cache flushes don't cause a race.
* Update all tests with new signatures. Removed a bunch of tests around TSM rewrites and WAL segment iteration that are no longer necessary.
Edd Robinson
Jason Wilder
Steven Hartland
Jon Seymour
Mark Rushakoff
Mark Rushakoff
INADA Naoki
Paul Dix
Philip O'Toole