sql: default to batch size 1 in allocator #62534
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This was referenced Mar 24, 2021
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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In cockroachdb#62534 it was shown that it takes up to two minutes before we have good enough statistics to allocate appropriately sized batches. However, the YCSB workloads only had a 1-minute ramp time, which would skew the results as throughput would abruptly change when the statistics were updated during the test. This patch changes the ramp time for YCSB workloads to 2 minutes to make sure we have appropriate statistics before starting the actual test. Release note: None
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In cockroachdb#62534 it was shown that it takes up to two minutes before we have good enough statistics to allocate appropriately sized batches. However, the YCSB workloads only had a 1-minute ramp time, which would skew the results as throughput would abruptly change when the statistics were updated during the test. This patch changes the ramp time for YCSB workloads to 2 minutes to make sure we have appropriate statistics before starting the actual test. Release note: None
This was referenced Mar 25, 2021
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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