This is an optimization on the existing append in OOOChunk.
What we've been doing so far is find the place inside the out-of-order
slice where the new sample should go in and then place it there and move
any samples to the right if necessary. This is OK but requires a binary
search every time the slice is bigger than 0.
The optimization is opinionated and suggests that although out-of-order
samples can be out-of-order amongst themselves they'll probably be in
order thus we can probably optimistically append at the end and if not
do the binary search.
OOOChunks are capped to 30 samples by default so this is a small
optimization but everything adds up, specially if you handle many active
timeseries with out-of-order samples.
Signed-off-by: Jesus Vazquez <jesus.vazquez@grafana.com>
Signed-off-by: Jesus Vazquez <jesusvazquez@users.noreply.github.com>
Co-authored-by: Ganesh Vernekar <ganeshvern@gmail.com>
* adapt code.go and write_handler.go to support float histograms
* adapt watcher.go to support float histograms
* wip adapt queue_manager.go to support float histograms
* address comments for metrics in queue_manager.go
* set test cases for queue manager
* use same counts for histograms and float histograms
* refactor createHistograms tests
* fix float histograms ref in watcher_test.go
* address PR comments
Signed-off-by: Marc Tuduri <marctc@protonmail.com>
In most cases, there is no sample at `maxt`, so `PeekBack` has to be
used. So far, `PeekBack` did not return a float histogram, and we
disregarded even any returned normal histogram. This fixes both, and
also tweaks the unit test to discover the problem (by using an earlier
timestamp than "now" for the samples in the TSDB).
Signed-off-by: beorn7 <beorn@grafana.com>
Extends Appender.AppendHistogram function to accept the FloatHistogram. TSDB supports appending, querying, WAL replay, for this new type of histogram.
Signed-off-by: Marc Tudurí <marctc@protonmail.com>
Signed-off-by: Ganesh Vernekar <ganeshvern@gmail.com>
Co-authored-by: Ganesh Vernekar <ganeshvern@gmail.com>
`QueueManager.externalLabels` becomes a slice rather than a `Labels` so
we can index into it when doing the merge operation.
Note we avoid calling `Labels.Len()` in `labelProtosToLabels()`.
It isn't necessary - `append()` will enlarge the buffer and we're
expecting to re-use it many times.
Also, we now validate protobuf input before converting to Labels.
This way we can detect errors first, and we don't place unnecessary
requirements on the Labels structure.
Re-do seriesFilter using labels.Builder (albeit N^2).
Signed-off-by: Bryan Boreham <bjboreham@gmail.com>
This is required to preserve the interface property of SeriesSet that says
"At returns full series. Returned series should be iterable even after Next is called."
Signed-off-by: sniper91 <kevinzhao91@outlook.com>
Re-use previous memory if it is already of the correct type.
In `NewListSeries` we hoist the conversion to an interface value out
so it only allocates once.
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>
The SeriesSets to be merged must be created each time round the loop,
otherwise the benchmark is not doing any real work.
Don't call ExpandSeries, because it spends most of its time allocating
a memory buffer to hold the result, which we don't look at.
Signed-off-by: Bryan Boreham <bjboreham@gmail.com>
Fix up merge test again
errors.Unwrap() actually dangerously returns nil if the error does not have an
Unwrap() method, which is the case in at least one of these places where I
noticed that no error was being logged at all when it should have.
Signed-off-by: Julius Volz <julius.volz@gmail.com>
* remote/read_handler: pool input to Marshal()
Use a sync.Pool to reuse byte slices between calls to Marshal() in the
remote read handler.
Signed-off-by: Giedrius Statkevičius <giedrius.statkevicius@vinted.com>
* remote: add microbenchmark for remote read handler
Signed-off-by: Giedrius Statkevičius <giedrius.statkevicius@vinted.com>
Signed-off-by: Giedrius Statkevičius <giedrius.statkevicius@vinted.com>
The wlog.WL type can now be used to create a Write Ahead Log or a Write
Behind Log.
Before the prefix for wbl metrics was
'prometheus_tsdb_out_of_order_wal_' and has been replaced with
'prometheus_tsdb_out_of_order_wbl_'.
Signed-off-by: Jesus Vazquez <jesus.vazquez@grafana.com>
Signed-off-by: Jesus Vazquez <jesusvazquez@users.noreply.github.com>
Co-authored-by: Ganesh Vernekar <15064823+codesome@users.noreply.github.com>
Where the code was multiplying bytes by number of operations, this
resulted in absurdly high throughput numbers.
Also, in `BenchmarkParse()`, don't run the `expfmt` case twice.
Signed-off-by: Bryan Boreham <bjboreham@gmail.com>
Use new experimental package `golang.org/x/exp/slices`.
slices.Sort works on values that are directly comparable, like ints,
so avoids the overhad of an interface call to `.Less()`.
Left tests unchanged, because they don't need the speed and it may be
a cross-check that slices.Sort gives the same answer.
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>
* Add runtime config to control native histogram ingestion
Signed-off-by: Ganesh Vernekar <ganeshvern@gmail.com>
* Make the config into a CLI flag
Signed-off-by: Ganesh Vernekar <ganeshvern@gmail.com>
Signed-off-by: Ganesh Vernekar <ganeshvern@gmail.com>
And a few cases of `EmptyLabels()`.
Replacing code which assumes the internal structure of `Labels`.
Signed-off-by: Bryan Boreham <bjboreham@gmail.com>
* Add histogram validation
Signed-off-by: Levi Harrison <git@leviharrison.dev>
* Correct negative offset validation
Signed-off-by: Levi Harrison <git@leviharrison.dev>
* Address review comments
Signed-off-by: Levi Harrison <git@leviharrison.dev>
* Validation benchmark
Signed-off-by: Levi Harrison <git@leviharrison.dev>
* Add more checks
Signed-off-by: Levi Harrison <git@leviharrison.dev>
* Attempt to fix tests
Signed-off-by: Levi Harrison <git@leviharrison.dev>
* Fix stuff
Signed-off-by: Levi Harrison <git@leviharrison.dev>
* Append metadata to the WAL
Signed-off-by: Paschalis Tsilias <paschalist0@gmail.com>
* Remove extra whitespace; Reword some docstrings and comments
Signed-off-by: Paschalis Tsilias <paschalist0@gmail.com>
* Use RLock() for hasNewMetadata check
Signed-off-by: Paschalis Tsilias <paschalist0@gmail.com>
* Use single byte for metric type in RefMetadata
Signed-off-by: Paschalis Tsilias <paschalist0@gmail.com>
* Update proposed WAL format for single-byte type metadata
Signed-off-by: Paschalis Tsilias <paschalist0@gmail.com>
* Implementa MetadataAppender interface for the Agent
Signed-off-by: Paschalis Tsilias <paschalist0@gmail.com>
* Address first round of review comments
Signed-off-by: Paschalis Tsilias <paschalist0@gmail.com>
* Amend description of metadata in wal.md
Signed-off-by: Paschalis Tsilias <paschalist0@gmail.com>
* Correct key used to retrieve metadata from cache
When we're setting metadata entries in the scrapeCace, we're using the
p.Help(), p.Unit(), p.Type() helpers, which retrieve the series name and
use it as the cache key. When checking for cache entries though, we used
p.Series() as the key, which included the metric name _with_ its labels.
That meant that we were never actually hitting the cache. We're fixing
this by utiling the __name__ internal label for correctly getting the
cache entries after they've been set by setHelp(), setType() or
setUnit().
Signed-off-by: Paschalis Tsilias <paschalist0@gmail.com>
* Put feature behind a feature flag
Signed-off-by: Paschalis Tsilias <paschalist0@gmail.com>
* Fix AppendMetadata docstring
Signed-off-by: Paschalis Tsilias <paschalist0@gmail.com>
* Reorder WAL format document
Signed-off-by: Paschalis Tsilias <paschalist0@gmail.com>
* Change error message of AppendMetadata; Fix access of s.meta in AppendMetadata
Signed-off-by: Paschalis Tsilias <paschalist0@gmail.com>
* Reuse temporary buffer in Metadata encoder
Signed-off-by: Paschalis Tsilias <paschalist0@gmail.com>
* Only keep latest metadata for each refID during checkpointing
Signed-off-by: Paschalis Tsilias <paschalist0@gmail.com>
* Fix test that's referencing decoding metadata
Signed-off-by: Paschalis Tsilias <paschalist0@gmail.com>
* Avoid creating metadata block if no new metadata are present
Signed-off-by: Paschalis Tsilias <paschalist0@gmail.com>
* Add tests for corrupt metadata block and relevant record type
Signed-off-by: Paschalis Tsilias <paschalist0@gmail.com>
* Fix CR comments
Signed-off-by: Paschalis Tsilias <paschalist0@gmail.com>
* Extract logic about changing metadata in an anonymous function
Signed-off-by: Paschalis Tsilias <paschalist0@gmail.com>
* Implement new proposed WAL format and amend relevant tests
Signed-off-by: Paschalis Tsilias <paschalist0@gmail.com>
* Use 'const' for metadata field names
Signed-off-by: Paschalis Tsilias <paschalist0@gmail.com>
* Apply metadata to head memSeries in Commit, not in AppendMetadata
Signed-off-by: Paschalis Tsilias <paschalist0@gmail.com>
* Add docstring and rename extracted helper in scrape.go
Signed-off-by: Paschalis Tsilias <paschalist0@gmail.com>
* Add tests for tsdb-related cases
Signed-off-by: Paschalis Tsilias <paschalist0@gmail.com>
* Fix linter issues vol1
Signed-off-by: Paschalis Tsilias <paschalist0@gmail.com>
* Fix linter issues vol2
Signed-off-by: Paschalis Tsilias <paschalist0@gmail.com>
* Fix Windows test by closing WAL reader files
Signed-off-by: Paschalis Tsilias <paschalist0@gmail.com>
* Use switch instead of two if statements in metadata decoding
Signed-off-by: Paschalis Tsilias <paschalist0@gmail.com>
* Fix review comments around TestMetadata* tests
Signed-off-by: Paschalis Tsilias <paschalist0@gmail.com>
* Add code for replaying WAL; test correctness of in-memory data after a replay
Signed-off-by: Paschalis Tsilias <paschalist0@gmail.com>
* Remove scrape-loop related code from PR
Signed-off-by: Paschalis Tsilias <paschalist0@gmail.com>
* Address first round of comments
Signed-off-by: Paschalis Tsilias <paschalist0@gmail.com>
* Simplify tests by sorting slices before comparison
Signed-off-by: Paschalis Tsilias <paschalist0@gmail.com>
* Fix test to use separate transactions
Signed-off-by: Paschalis Tsilias <paschalist0@gmail.com>
* Empty out buffer and record slices after encoding latest metadata
Signed-off-by: Paschalis Tsilias <paschalist0@gmail.com>
* Fix linting issue
Signed-off-by: Paschalis Tsilias <paschalist0@gmail.com>
* Update calculation for DroppedMetadata metric
Signed-off-by: Paschalis Tsilias <paschalist0@gmail.com>
* Rename MetadataAppender interface and AppendMetadata method to MetadataUpdater/UpdateMetadata
Signed-off-by: Paschalis Tsilias <paschalist0@gmail.com>
* Reuse buffer when encoding latest metadata for each series
Signed-off-by: Paschalis Tsilias <paschalist0@gmail.com>
* Fix review comments; Check all returned error values using two helpers
Signed-off-by: Paschalis Tsilias <paschalist0@gmail.com>
* Simplify use of helpers
Signed-off-by: Paschalis Tsilias <paschalist0@gmail.com>
* Satisfy linter
Signed-off-by: Paschalis Tsilias <paschalist0@gmail.com>
Note: This is deliberately an incompatible change. Since we have never
used histograms in remote read/write yet, there is no point in keeping
compatibility. This _is_, however, compatible to the state in the main
branch.
This commit flattens the bucket message into top-level fields. This
has the disadvantage of now having two triples of fields prefixed with
`negative_...` or `positive_...`. However, with this structure, we
save one tag on the wire. And, perhaps more importantly, we mirror the
structure of the `histogram.Histogram` Go type.
This commit also adjusts `repeated` fields to use names in the plural
form, as it is also the case for the fields that already existed.
This also adds a doc comment to `HistogramProtoToHistogram` and
changes its return type to a pointer (which is more convenient and
probably more efficient).
Signed-off-by: beorn7 <beorn@grafana.com>
* Removing global state modification on unit tests (fix#10033#10034)
The config.DefaultRemoteReadConfig and config.DefaultRemoteWriteConfig
instances hold global state. Unit tests were changing their url.URL reference
globally causing false positives when tests were ran through package.
Two helper functions were created to copy those global values instead of changing
them in place to fix null point when running unit tests by method instead of
by package.
Signed-off-by: Leonardo Zamariola <leonardo.zamariola@gmail.com>
* Fixing pull request suggestions
Copying by value from default config
Signed-off-by: Leonardo Zamariola <leonardo.zamariola@gmail.com>
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.
Signed-off-by: Ganesh Vernekar <ganeshvern@gmail.com>
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>
* Rename walDir parameter to dir
Signed-off-by: Matej Gera <matejgera@gmail.com>
* Improve NewQueueManager comment
Signed-off-by: Matej Gera <matejgera@gmail.com>
"Labels is a sorted set of labels. Order has to be guaranteed upon
instantiation." says the comment, so fix all the tests that break this
rule.
For `BenchmarkLabelValuesWithMatchers()` and
`BenchmarkHeadLabelValuesWithMatchers()` the amount of work done changes
significantly if you put the labels in order, because all series refs
get neatly partitioned by the `tens` label, so I renamed the labels
to maintain the previous behaviour.
Signed-off-by: Bryan Boreham <bjboreham@gmail.com>
* refactor: move from io/ioutil to io and os packages
* use fs.DirEntry instead of os.FileInfo after os.ReadDir
Signed-off-by: MOREL Matthieu <matthieu.morel@cnp.fr>
If FlushAndShutdown is called with a full batchQueue, and then Batch is
called rather than the normal path of reading from a queue a deadlock
might be encountered. Rather than having FlushAndShutdown having
blocking code while holding a lock retry sending the batch every second.
Signed-off-by: Chris Marchbanks <csmarchbanks@gmail.com>
Do not block when trying to write a batch to the queue. This can cause
appends to lock forever if the only thing reading from the queue needs
the mutex to write. Instead, if batchQueue is full pop the sample that
was just added from the partial batch and return false. The code doing
the appending already handles retries with backoff.
Signed-off-by: Chris Marchbanks <csmarchbanks@gmail.com>
* Run gofumpt on all files
Getting golangci-lint errors when building on my laptop, possibly because I have newer version of gofumpt then what it was formatted with.
Run gofumpt -w -extra on all files as it will be needed in the future anyway.
* Update golangci-lint to v1.44.2
v1.44.0 upgraded gofumpt so bumping version in CI will help keep formatting correct for everyone
* Address golangci-lint error
Getting 'error-strings: error strings should not be capitalized or end with punctuation or a newline' from revive here.
Drop new line.
Signed-off-by: Łukasz Mierzwa <l.mierzwa@gmail.com>
If a queue is stopped and one of its shards happens to hit the
batch_send_deadline at the same time a deadlock can occur where stop
holds the mutex and will not release it until the send is finished, but
the send needs the mutex to retrieve the most recent batch. This is
fixed by using a second mutex just for writing.
In addition, the test I wrote exposed a case where during shutdown a
batch could be sent twice due to concurrent calls to queue.Batch() and
queue.FlushAndShutdown(). Protect these with a mutex as well.
Signed-off-by: Chris Marchbanks <csmarchbanks@gmail.com>
Previously we would reject an increase from 2 to 2.5 as being
within 30%; by rounding up first we see this as an increase from 2 to 3.
Signed-off-by: Bryan Boreham <bjboreham@gmail.com>
Change the coefficient from 1% to 5%, so instead of targetting to clear
the backlog in 100s we target 20s.
Update unit test to reflect the new behaviour.
Signed-off-by: Bryan Boreham <bjboreham@gmail.com>
We have an alert that fires when prometheus_remote_storage_highest_timestamp_in_seconds - prometheus_remote_storage_queue_highest_sent_timestamp_seconds
becomes too high. But we have an agent that fires this when the remote "rate-limits" the user.
This is because prometheus_remote_storage_queue_highest_sent_timestamp_seconds doesn't get updated
when the remote sends a 429.
I think we should update the metrics, and the change I made makes sense. Because if the requests fails
because of connectivity issues, etc. we will never exit the `sendWriteRequestWithBackoff` function. It only
exits the function when there is a non-recoverable error, like a bad status code, and in that case, I think
the metric needs to be updated.
Signed-off-by: Goutham Veeramachaneni <gouthamve@gmail.com>
* storage: expose bug in iterators #10027
Signed-off-by: beorn7 <beorn@grafana.com>
* storage: fix bug #10027 in iterators' Seek method
Signed-off-by: beorn7 <beorn@grafana.com>
* Append reporting metrics without limit
If reporting metrics fails due to reaching the limit, this makes the
target appear as UP in the UI, but the metrics are missing.
This commit bypasses that limit for report metrics.
Signed-off-by: Julien Pivotto <roidelapluie@inuits.eu>
* Remove check against cfg so interval/ timeout are always set (#10023) (#10031)
Signed-off-by: Nicholas Blott <blottn@tcd.ie>
Co-authored-by: Nicholas Blott <blottn@tcd.ie>
* Cut v2.32.1
Signed-off-by: Julius Volz <julius.volz@gmail.com>
* Apply suggestions from code review
Signed-off-by: Julius Volz <julius.volz@gmail.com>
Co-authored-by: Levi Harrison <git@leviharrison.dev>
Co-authored-by: Julien Pivotto <roidelapluie@inuits.eu>
Co-authored-by: Nicholas Blott <blottn@tcd.ie>
Co-authored-by: Julius Volz <julius.volz@gmail.com>
Co-authored-by: Levi Harrison <git@leviharrison.dev>
Previously BenchmarkSampleDelivery spent a lot of effort checking each
sample had arrived, so was largely showing the performance of test-only
code.
Increase the number of shards to be more realistic for a large
workload.
Signed-off-by: Bryan Boreham <bjboreham@gmail.com>
Right now the values for enqueuedSamples and enqueuedExemplars is never
subtracted leading to inflated values for failedSamples/failedExemplars
when a hard shutdown of a shard occurs.
Signed-off-by: Chris Marchbanks <csmarchbanks@gmail.com>
Channels can cause bottlenecks and tons of context switches when reading
hundreds of thousands of samples per second from a single queue.
Instead, pre-batch the samples to amortize the cost of the concurrency
overhead.
Signed-off-by: Chris Marchbanks <csmarchbanks@gmail.com>
