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| -rw-r--r-- | doc/src/sgml/ref/vacuumdb.sgml | 16 |
1 files changed, 10 insertions, 6 deletions
diff --git a/doc/src/sgml/ref/vacuumdb.sgml b/doc/src/sgml/ref/vacuumdb.sgml index 223b986b920..d8cbf0e189d 100644 --- a/doc/src/sgml/ref/vacuumdb.sgml +++ b/doc/src/sgml/ref/vacuumdb.sgml @@ -398,15 +398,19 @@ PostgreSQL documentation <para> Only calculate statistics for use by the optimizer (no vacuum), like <option>--analyze-only</option>. Run several (currently three) - stages of analyze with different configuration settings, to produce - usable statistics faster. + stages of analyze; the first stage uses the lowest possible statistics + target (see <xref linkend="guc-default-statistics-target"/>) + to produce usable statistics faster, and subsequent stages build the + full statistics. </para> <para> - This option is useful to analyze a database that was newly populated - from a restored dump or by <command>pg_upgrade</command>. This option - will try to create some statistics as fast as possible, to make the - database usable, and then produce full statistics in the subsequent + This option is only useful to analyze a database that current has + no statistics or wholly incorrect ones, such as if it is newly + populated from a restored dump or by <command>pg_upgrade</command>. + Be aware that running this option in a database with existing + statistics may cause the query optimizer choices to become + transiently worse due to the low statistics targets of the early stages. </para> </listitem> |