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Improve contrib/pg_stat_statements to lump "similar" queries together.
pg_stat_statements now hashes selected fields of the analyzed parse treeto assign a "fingerprint" to each query, and groups all queries with thesame fingerprint into a single entry in the pg_stat_statements view.In practice it is expected that queries with the same fingerprint will beequivalent except for values of literal constants. To make the displaymore useful, such constants are replaced by "?" in the displayed querystrings.This mechanism currently supports only optimizable queries (SELECT,INSERT, UPDATE, DELETE). Utility commands are still matched on thebasis of their literal query strings.There remain some open questions about how to deal with utility statementsthat contain optimizable queries (such as EXPLAIN and SELECT INTO) and howto deal with expiring speculative hashtable entries that are made to savethe normalized form of a query string. However, fixing these issues shouldrequire only localized changes, and since there are other open patchesinvolving contrib/pg_stat_statements, it seems best to go ahead and commitwhat we've got.Peter Geoghegan, reviewed by Daniel Farina1 parent4e1c720 commit7313cc0
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