diff options
Diffstat (limited to 'doc/src')
| -rw-r--r-- | doc/src/sgml/config.sgml | 35 |
1 files changed, 27 insertions, 8 deletions
diff --git a/doc/src/sgml/config.sgml b/doc/src/sgml/config.sgml index ffea744cb8c..c4afd148c5c 100644 --- a/doc/src/sgml/config.sgml +++ b/doc/src/sgml/config.sgml @@ -1893,15 +1893,34 @@ include_dir 'conf.d' </term> <listitem> <para> - When no tuples were deleted from the heap, B-tree indexes might still - be scanned during <command>VACUUM</command> cleanup stage by two - reasons. The first reason is that B-tree index contains deleted pages - which can be recycled during cleanup. The second reason is that B-tree - index statistics is stalled. The criterion of stalled index statistics - is number of inserted tuples since previous statistics collection - is greater than <varname>vacuum_cleanup_index_scale_factor</varname> - fraction of total number of heap tuples. + Specifies the fraction of the total number of heap tuples counted in + the previous statistics collection that can be inserted without + incurring an index scan at the <command>VACUUM</command> cleanup stage. + This setting currently applies to B-tree indexes only. </para> + + <para> + If no tuples were deleted from the heap, B-tree indexes are still + scanned at the <command>VACUUM</command> cleanup stage when at least one + of the following conditions is met: the index statistics are stale, or + the index contains deleted pages that can be recycled during cleanup. + Index statistics are considered to be stale if the number of newly + inserted tuples exceeds the <varname>vacuum_cleanup_index_scale_factor</varname> + fraction of the total number of heap tuples detected by the previous + statistics collection. The total number of heap tuples is stored in + the index meta-page. Note that the meta-page does not include this data + until <command>VACUUM</command> finds no dead tuples, so B-tree index + scan at the cleanup stage can only be skipped if the second and + subsequent <command>VACUUM</command> cycles detect no dead tuples. + </para> + + <para> + The value can range from <literal>0</literal> to <literal>100</literal>. + When <varname>vacuum_cleanup_index_scale_factor</varname> is set to + <literal>0</literal>, index scans are never skipped during + <command>VACUUM</command> cleanup. The default value is <literal>0.1</literal>. + </para> + </listitem> </varlistentry> </variablelist> |