sql: improve the SHOW TABLES query to avoid reading stats when unused #59838
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rytaft
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Feb 5, 2021
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Reviewed 2 of 2 files at r1.
Reviewable status:complete! 1 of 0 LGTMs obtained (waiting on @rafiss)
rafiss
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Feb 5, 2021
| LEFT JOIN crdb_internal.table_row_statistics AS s ON (s.table_id = pc.oid::INT8) | ||
| LEFT JOIN | ||
| ( | ||
| SELECT DISTINCT ON (table_id) table_id, estimated_row_count FROM crdb_internal.table_row_statistics |
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out of curiosity, do we achieve the same thing by adding a crdb_internal.table_row_statistics(table_id) virtual index? i forget if virtual indexes are required to be unique
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I don't think they are unique indexes.
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ah i misread the intention of this. do you mind backporting it too? thanks! |
There is a distinct relationship between tables and row statistics which was previously not stated explicitly in the query and thus, the optimizer was unable to eliminate the join against the statistics table when the `estimated_row_count` column was not used. Release note (performance improvement): Queries which use `SHOW TABLES` but do not utilize the `estimated_row_count` column no longer need to look up the table statistics.
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There is a distinct relationship between tables and row statistics which
was previously not stated explicitly in the query and thus, the optimizer
was unable to eliminate the join against the statistics table when the
estimated_row_countcolumn was not used.Touches #58189.
Release note (performance improvement): Queries which use
SHOW TABLESbutdo not utilize the
estimated_row_countcolumn no longer need to look upthe table statistics.