sql, opt: avoid full scans in mutation queries with cost flags #137984
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I'm looking into this. |
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Ditto |
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Reviewable status:
complete! 0 of 0 LGTMs obtained
pkg/sql/opt/xform/testdata/rules/limit line 2770 at r4 (raw file):
Previously, rytaft (Rebecca Taft) wrote…
I'm looking into this.
This is an unrelated bug: #137994
pkg/sql/opt/xform/testdata/rules/limit line 2844 at r4 (raw file):
Previously, rytaft (Rebecca Taft) wrote…
Ditto
See #137994
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Happy to bikeshed on names here -- maybe the "Cost" data member should just be "C"? |
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Great idea!
Reviewed 24 of 24 files at r1, 24 of 24 files at r2, 84 of 84 files at r3, 1 of 1 files at r4, all commit messages.
Reviewable status:
pkg/sql/opt/memo/cost.go line 14 at r4 (raw file):
Previously, rytaft (Rebecca Taft) wrote…
Happy to bikeshed on names here -- maybe the "Cost" data member should just be "C"?
I like C. 👍
pkg/sql/opt/xform/testdata/rules/limit line 2770 at r4 (raw file):
Previously, rytaft (Rebecca Taft) wrote…
This is an unrelated bug: #137994
I'm worried this change makes this bad plan more likely to hit, so I'm going to label that bug a GA-blocker for now.
pkg/sql/opt/memo/cost.go line 53 at r2 (raw file):
type CostFlags struct { FullScanPenalty bool HugeCostPenalty bool
nit: an explanation of each of these might be useful
pkg/sql/opt/xform/coster.go line 193 at r2 (raw file):
// If the final expression has this cost or larger, it means that there was no // plan that could satisfy the hints. hugeCost = memo.Cost{Cost: 1e100, Flags: memo.CostFlags{HugeCostPenalty: true}}
Do we still need the 1e100 cost for hugeCost?
pkg/ccl/logictestccl/testdata/logic_test/multi_region_remote_access_error line 505 at r3 (raw file):
# Delete accessing all regions should fail. retry statement error pq: Query has no home region\. Try adding a filter on messages_rbr\.crdb_region and/or on key column \(messages_rbr\.message\)\. For more information, see https://www.cockroachlabs.com/docs/stable/cost-based-optimizer.html#control-whether-queries-are-limited-to-a-single-region
Any idea why this changed?
This is a mechanical change that will set up the ability to use CostFlags in a future commit. Release note: None
Added a hint to avoid full scans (see release note below for details). To support this change, added a field to memo.Cost with a new type memo.CostFlags, which contains a number of boolean flags and supports "multi-dimensional costing". This allows the optimizer to compare plans based on the flags set in addition to the single-dimensional float64 cost. For example, plans with the new FullScanPenalty cost flag enabled will always be more expensive than plans without any cost flags, even if the base float64 cost is lower. The new CostFlags type also includes a flag for HugeCostPenalty, which must be set for plans with "hugeCost". This ensures that existing hints that use hugeCost still work if some other cost flags are set, since HugeCostPenalty takes precedence over other cost flags. This new CostFlags field is needed to support hints that do not cause an error if the optimizer cannot find a plan complying with the hint. This is needed because the previous approach of simply using "hugeCost" to avoid certain plans meant that if such plans were unavoidable, we could not effectively compare plans with cost greater than hugeCost due to loss of floating point precision. Informs cockroachdb#79683 Release note (sql change): Added support for a new index hint, AVOID_FULL_SCAN, which will prevent the optimizer from planning a full scan for the specified table if any other plan is possible. The hint can be used in the same way as other existing index hints. For example, SELECT * FROM table_name@{AVOID_FULL_SCAN};. This hint is similar to NO_FULL_SCAN, but will not error if a full scan cannot be avoided. Note that normally a full scan of a partial index would not be considered a "full scan" for the purposes of the NO_FULL_SCAN and AVOID_FULL_SCAN hints, but if the user has explicitly forced the partial index via FORCE_INDEX=index_name, we do consider it a full scan.
Fixes cockroachdb#79683 Release note (sql change): Added a new session setting avoid_full_table_scans_in_mutations, which when set to true, causes the optimizer to avoid planning full table scans for mutation queries if any other plan is possible. It now defaults to true.
Removed a comment that references a function parameter that no longer exists. Release note: None
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opt: convert
memo.Costto a struct withCostFlagsThis is a mechanical change that will set up the ability to use
CostFlagsin a future commit.Release note: None
opt,sql: support hint to avoid full scan
Added a hint to avoid full scans (see release note below for details).
To support this change, added a field to
memo.Costwith a new typememo.CostFlags, which contains a number of boolean flags and supports"multi-dimensional costing". This allows the optimizer to compare plans
based on the flags set in addition to the single-dimensional float64
cost. For example, plans with the new
FullScanPenaltycost flag enabledwill always be more expensive than plans without any cost flags, even
if the base float64 cost is lower.
The new
CostFlagstype also includes a flag forHugeCostPenalty, whichmust be set for plans with
hugeCost. This ensures that existinghints that use
hugeCoststill work if some other cost flags are set,since
HugeCostPenaltytakes precedence over other cost flags.This new
CostFlagsfield is needed to support hints that do not cause anerror if the optimizer cannot find a plan complying with the hint. This
is needed because the previous approach of simply using
hugeCosttoavoid certain plans meant that if such plans were unavoidable, we could
not effectively compare plans with cost greater than
hugeCostdue toloss of floating point precision.
Informs #79683
Release note (sql change): Added support for a new index hint,
AVOID_FULL_SCAN, which will prevent the optimizer from planning afull scan for the specified table if any other plan is possible. The
hint can be used in the same way as other existing index hints. For
example,
SELECT * FROM table_name@{AVOID_FULL_SCAN};. This hint issimilar to
NO_FULL_SCAN, but will not error if a full scan cannot beavoided. Note that normally a full scan of a partial index would not
be considered a "full scan" for the purposes of the
NO_FULL_SCANandAVOID_FULL_SCANhints, but if the user has explicitly forced thepartial index via
FORCE_INDEX=index_name, we do consider it a fullscan.
sql,opt: add setting
avoid_full_table_scans_in_mutationsFixes #79683
Release note (sql change): Added a new session setting
avoid_full_table_scans_in_mutations, which when set to true, causesthe optimizer to avoid planning full table scans for mutation queries
if any other plan is possible. It now defaults to true.
opt: remove a stale comment above
optbuilder.buildScanRemoved a comment that references a function parameter that no longer
exists.
Release note: None