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release-22.1: sql: reduce the overhead of EXPLAIN ANALYZE #91209

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yuzefovich
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@yuzefovich yuzefovich commented Nov 3, 2022

Backport 1/1 commits from #91117.

/cc @cockroachdb/release


In order to propagate the execution stats across the distributed query plan we use the tracing infrastructure, where each stats object is added as "structured metadata" to the trace. Thus, whenever we're collecting the exec stats for a statement, we must enable tracing. Previously, in many cases we would enable it at the highest verbosity level which has non-trivial overhead. In some cases this was an overkill (e.g. in EXPLAIN ANALYZE we don't really care about the trace containing all of the gory details - we won't expose it anyway), so this is now fixed by using the less verbose "structured" verbosity level. As a concrete example of the difference: for a stmt that without EXPLAIN ANALYZE takes around 190ms, with EXPLAIN ANALYZE it would previously run for about 1.8s and now it takes around 210ms.

This required some minor changes to the row-by-row outbox and router
setups to collect thats even if the recording is not verbose.

Addresses: #90739.

Epic: None

Release note (performance improvement): The overhead of running EXPLAIN ANALYZE and EXPLAIN ANALYZE (DISTSQL) has been significantly reduced. The overhead of EXPLAIN ANALYZE (DEBUG) didn't change.

Release justification: performance fix.

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blathers-crl bot commented Nov 3, 2022

Thanks for opening a backport.

Please check the backport criteria before merging:

  • Patches should only be created for serious issues or test-only changes.
  • Patches should not break backwards-compatibility.
  • Patches should change as little code as possible.
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  • Patches should not add new functionality.
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If some of the basic criteria cannot be satisfied, ensure that the exceptional criteria are satisfied within.
  • There is a high priority need for the functionality that cannot wait until the next release and is difficult to address in another way.
  • The new functionality is additive-only and only runs for clusters which have specifically “opted in” to it (e.g. by a cluster setting).
  • New code is protected by a conditional check that is trivial to verify and ensures that it only runs for opt-in clusters.
  • The PM and TL on the team that owns the changed code have signed off that the change obeys the above rules.

Add a brief release justification to the body of your PR to justify this backport.

Some other things to consider:

  • What did we do to ensure that a user that doesn’t know & care about this backport, has no idea that it happened?
  • Will this work in a cluster of mixed patch versions? Did we test that?
  • If a user upgrades a patch version, uses this feature, and then downgrades, what happens?

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@DrewKimball DrewKimball left a comment

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:lgtm:

Reviewable status: :shipit: complete! 1 of 0 LGTMs obtained (waiting on @michae2)

In order to propagate the execution stats across the distributed query
plan we use the tracing infrastructure, where each stats object is added
as "structured metadata" to the trace. Thus, whenever we're collecting
the exec stats for a statement, we must enable tracing. Previously, in
many cases we would enable it at the highest verbosity level which has
non-trivial overhead. In some cases this was an overkill (e.g. in
`EXPLAIN ANALYZE` we don't really care about the trace containing all of
the gory details - we won't expose it anyway), so this is now fixed by
using the less verbose "structured" verbosity level. As a concrete
example of the difference: for a stmt that without `EXPLAIN ANALYZE`
takes around 190ms, with `EXPLAIN ANALYZE` it would previously run for
about 1.8s and now it takes around 210ms.

This required some minor changes to the row-by-row outbox and router
setups to collect thats even if the recording is not verbose.

Release note (performance improvement): The overhead of running
`EXPLAIN ANALYZE` and `EXPLAIN ANALYZE (DISTSQL)` has been significantly
reduced. The overhead of `EXPLAIN ANALYZE (DEBUG)` didn't change.
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Unfortunately, we cannot easily backport this because we'd start losing some of the execution stats (as the failures here show) - see for more context.

@yuzefovich yuzefovich closed this Nov 7, 2022
@yuzefovich yuzefovich deleted the backport22.1-91117 branch November 7, 2022 20:16
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3 participants