opt: add settings to enable usage of histograms and multi-column stats #48105
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RaduBerinde
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Apr 28, 2020
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Reviewable status:
complete! 1 of 0 LGTMs obtained (waiting on @RaduBerinde and @rytaft)
pkg/sql/exec_util.go, line 193 at r1 (raw file):
var optUseHistogramsClusterMode = settings.RegisterBoolSetting( "sql.defaults.optimizer_use_histograms.enabled", "default value for optimizer_use_histograms session setting; enables usage of histograms in the optimizer by default",
add a note that it doesn't disable collection, and mention the other setting for the collection
pkg/sql/exec_util.go, line 199 at r1 (raw file):
var optUseMultiColStatsClusterMode = settings.RegisterBoolSetting( "sql.defaults.optimizer_use_multicol_stats.enabled", "default value for optimizer_use_multicol_stats session setting; enables usage of multi-column stats in the optimizer by default",
ditto
Prior to this commit, histograms and multi-column stats were always used by the optimizer for cardinality estimation if they were available. This commit adds two new session settings along with two corresponding cluster settings to control whether or not the optimizer should use histograms or multi-column stats. Note that even if the settings are enabled, the optimizer cannot use these statistics if they haven't been collected. Collection of histograms and multi-column stats is still controlled by the existing cluster settings `sql.stats.histogram_collection.enabled` and `sql.stats.multi_column_collection.enabled`. The new settings to control usage by the optimizer are: Cluster settings: ``` sql.defaults.optimizer_use_histograms.enabled sql.defaults.optimizer_use_multicol_stats.enabled ``` Session settings: ``` optimizer_use_histograms optimizer_use_multicol_stats ``` Both settings are enabled by default. Fixes cockroachdb#43308 Informs cockroachdb#38082 Informs cockroachdb#34422 Release note (sql change): Added two new session settings and corresponding cluster settings to control whether the optimizer uses histograms and multi-column statistics for cardinality estimation. The session settings are optimizer_use_histograms and optimizer_use_multicol_stats, with corresponding cluster settings sql.defaults.optimizer_use_histograms.enabled and sql.defaults.optimizer_use_multicol_stats.enabled. Both settings are enabled by default.
rytaft
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Apr 28, 2020
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TFTR!
bors r+
Reviewable status:
pkg/sql/exec_util.go, line 193 at r1 (raw file):
Previously, RaduBerinde wrote…
add a note that it doesn't disable collection, and mention the other setting for the collection
Done.
pkg/sql/exec_util.go, line 199 at r1 (raw file):
Previously, RaduBerinde wrote…
ditto
Done.
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Prior to this commit, histograms and multi-column stats were always used
by the optimizer for cardinality estimation if they were available. This
commit adds two new session settings along with two corresponding cluster
settings to control whether or not the optimizer should use histograms or
multi-column stats.
Note that even if the settings are enabled, the optimizer cannot use these
statistics if they haven't been collected. Collection of histograms and
multi-column stats is still controlled by the existing cluster settings
sql.stats.histogram_collection.enabledandsql.stats.multi_column_collection.enabled.The new settings to control usage by the optimizer are:
Cluster settings:
Session settings:
Both settings are enabled by default.
Fixes #43308
Informs #38082
Informs #34422
Release note (sql change): Added two new session settings and corresponding
cluster settings to control whether the optimizer uses histograms and
multi-column statistics for cardinality estimation. The session settings
are optimizer_use_histograms and optimizer_use_multicol_stats, with
corresponding cluster settings sql.defaults.optimizer_use_histograms.enabled
and sql.defaults.optimizer_use_multicol_stats.enabled. Both settings are
enabled by default.