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Diffstat (limited to 'doc/src/sgml/ref/analyze.sgml')
| -rw-r--r-- | doc/src/sgml/ref/analyze.sgml | 13 |
1 files changed, 12 insertions, 1 deletions
diff --git a/doc/src/sgml/ref/analyze.sgml b/doc/src/sgml/ref/analyze.sgml index 418082e6d93..c0d2673dc50 100644 --- a/doc/src/sgml/ref/analyze.sgml +++ b/doc/src/sgml/ref/analyze.sgml @@ -1,5 +1,5 @@ <!-- -$PostgreSQL: pgsql/doc/src/sgml/ref/analyze.sgml,v 1.25 2008/12/13 19:13:44 tgl Exp $ +$PostgreSQL: pgsql/doc/src/sgml/ref/analyze.sgml,v 1.26 2009/08/02 22:14:51 tgl Exp $ PostgreSQL documentation --> @@ -165,6 +165,17 @@ ANALYZE [ VERBOSE ] [ <replaceable class="PARAMETER">table</replaceable> [ ( <re the target causes a proportional increase in the time and space needed to do <command>ANALYZE</command>. </para> + + <para> + One of the values estimated by <command>ANALYZE</command> is the number of + distinct values that appear in each column. Because only a subset of the + rows are examined, this estimate can sometimes be quite inaccurate, even + with the largest possible statistics target. If this inaccuracy leads to + bad query plans, a more accurate value can be determined manually and then + installed with + <command>ALTER TABLE ... ALTER COLUMN ... SET STATISTICS DISTINCT</> + (see <xref linkend="sql-altertable" endterm="sql-altertable-title">). + </para> </refsect1> <refsect1> |