Reduce chunk batch iterator BatchSize - #7823
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Signed-off-by: Paurush Garg <paurushg@amazon.com>
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| // BatchSize is samples per batch; this was choose by benchmarking all sizes from | ||
| // 1 to 128. | ||
| const BatchSize = 12 | ||
| const BatchSize = 8 |
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What this PR does:
Each
newMergeIteratorallocatesbatchesandbatchesBufslices sized by the number of chunk partitions (typically 3 with replication factor 3). WithBatchSize=12, eachBatchstruct is 384 bytes, giving a per-iterator cost of ~2,560 bytes. WithBatchSize=8, eachBatchstruct is 256 bytes, reducing per-iterator cost to ~1,792 bytes (~30% reduction).This matters for query engines that allocate all iterators upfront - one per series - and hold them alive for the duration of the query. At high cardinality (millions of series), the cumulative merge iterator allocation becomes the dominant heap consumer. Reducing the per-iterator footprint directly reduces heap pressure under concurrent high-cardinality queries.
Benchmark
#7823 (comment)
Seeks (15s - 60s): ~1.5-2% slower
Seeks (300s - 6000s): 3-9% faster
geomean: −1.5%
Which issue(s) this PR fixes:
Fixes #
Checklist
CHANGELOG.mdupdated - the order of entries should be[CHANGE],[FEATURE],[ENHANCEMENT],[BUGFIX]docs/configuration/v1-guarantees.mdupdated if this PR introduces experimental flags