release-21.1: sql: default to batch size 1 in allocator #62603
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rytaft
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Mar 25, 2021
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Reviewed 1 of 1 files at r1.
Reviewable status:complete! 1 of 0 LGTMs obtained (waiting on @jordanlewis)
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Oh yeah, Jordan has a fix for it. |
In cockroachdb#62282, the estimated row count was passed into the scan batch allocator to avoid growing the batch from 1. However, this also changed the default batch size from 1 to 1024 when no row count estimate was available, giving significant overhead when fetching small result sets. On `kv95/enc=false/nodes=1/cpu=32` this reduced performance from 66304 ops/s to 58862 ops/s (median of 5 runs), since these are single-row reads without estimates. This patch reverts the default batch size to 1 when no row count estimate is available. This fully fixes the `kv95` performance regression. YCSB/E takes a small hit going from 1895 ops/s to 1786 ops/s, but this only seems to happen because it takes a while for the statistics to update: sometime within the first minute of the test (after the 1-minute ramp-up period), throughput abruptly changes from ~700 ops/s to ~1800 ops/s, so using a 2-minute ramp-up period in roachtest would mostly eliminate any difference. Release note: None
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Backport 1/1 commits from #62534.
/cc @cockroachdb/release
In #62282, the estimated row count was passed into the scan batch
allocator to avoid growing the batch from 1. However, this also changed
the default batch size from 1 to 1024 when no row count estimate was
available, giving significant overhead when fetching small result sets.
On
kv95/enc=false/nodes=1/cpu=32this reduced performance from 66304ops/s to 58862 ops/s (median of 5 runs), since these are single-row
reads without estimates.
This patch reverts the default batch size to 1 when no row count
estimate is available. This fully fixes the
kv95performanceregression. YCSB/E takes a small hit going from 1895 ops/s to 1786
ops/s, but this only seems to happen because it takes a while for the
statistics to update: sometime within the first minute of the test
(after the 1-minute ramp-up period), throughput abruptly changes from
~700 ops/s to ~1800 ops/s, so using a 2-minute ramp-up period in
roachtest would mostly eliminate any difference.
Resolves #62524.
Release note: None