Various improvements of skipping index scan during vacuum technics
- Change vacuum_cleanup_index_scale_factor GUC to PGC_USERSET. vacuum_cleanup_index_scale_factor GUC was defined as PGC_SIGHUP. But this GUC affects not only autovacuum. So it might be useful to change it from user session in order to influence manually runned VACUUM. - Add missing tab-complete support for vacuum_cleanup_index_scale_factor reloption. - Fix condition for B-tree index cleanup. Zero value of vacuum_cleanup_index_scale_factor means that user wants B-tree index cleanup to be never skipped. - Documentation and comment improvements Authors: Justin Pryzby, Alexander Korotkov, Liudmila Mantrova Reviewed by: all authors and Robert Haas Discussion: https://www.postgresql.org/message-id/flat/20180502023025.GD7631%40telsasoft.com
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Teodor Sigaev
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8e12f4a250
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@ -1893,15 +1893,34 @@ include_dir 'conf.d'
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</term>
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<listitem>
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<para>
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When no tuples were deleted from the heap, B-tree indexes might still
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be scanned during <command>VACUUM</command> cleanup stage by two
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reasons. The first reason is that B-tree index contains deleted pages
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which can be recycled during cleanup. The second reason is that B-tree
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index statistics is stalled. The criterion of stalled index statistics
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is number of inserted tuples since previous statistics collection
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is greater than <varname>vacuum_cleanup_index_scale_factor</varname>
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fraction of total number of heap tuples.
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Specifies the fraction of the total number of heap tuples counted in
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the previous statistics collection that can be inserted without
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incurring an index scan at the <command>VACUUM</command> cleanup stage.
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This setting currently applies to B-tree indexes only.
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</para>
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<para>
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If no tuples were deleted from the heap, B-tree indexes are still
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scanned at the <command>VACUUM</command> cleanup stage when at least one
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of the following conditions is met: the index statistics are stale, or
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the index contains deleted pages that can be recycled during cleanup.
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Index statistics are considered to be stale if the number of newly
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inserted tuples exceeds the <varname>vacuum_cleanup_index_scale_factor</varname>
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fraction of the total number of heap tuples detected by the previous
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statistics collection. The total number of heap tuples is stored in
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the index meta-page. Note that the meta-page does not include this data
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until <command>VACUUM</command> finds no dead tuples, so B-tree index
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scan at the cleanup stage can only be skipped if the second and
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subsequent <command>VACUUM</command> cycles detect no dead tuples.
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</para>
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<para>
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The value can range from <literal>0</literal> to <literal>100</literal>.
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When <varname>vacuum_cleanup_index_scale_factor</varname> is set to
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<literal>0</literal>, index scans are never skipped during
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<command>VACUUM</command> cleanup. The default value is <literal>0.1</literal>.
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</para>
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</listitem>
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</varlistentry>
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</variablelist>
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@ -189,7 +189,7 @@ _bt_update_meta_cleanup_info(Relation rel, TransactionId oldestBtpoXact,
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if (metad->btm_version < BTREE_VERSION)
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_bt_upgrademetapage(metapg);
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/* update cleanup-related infromation */
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/* update cleanup-related information */
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metad->btm_oldest_btpo_xact = oldestBtpoXact;
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metad->btm_last_cleanup_num_heap_tuples = numHeapTuples;
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MarkBufferDirty(metabuf);
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@ -818,10 +818,11 @@ _bt_vacuum_needs_cleanup(IndexVacuumInfo *info)
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float8 cleanup_scale_factor;
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/*
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* If table receives large enough amount of insertions and no cleanup
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* was performed, then index might appear to have stalled statistics.
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* In order to evade that, we perform cleanup when table receives
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* vacuum_cleanup_index_scale_factor fractions of insertions.
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* If table receives enough insertions and no cleanup was performed,
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* then index would appear have stale statistics. If scale factor
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* is set, we avoid that by performing cleanup if the number of
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* inserted tuples exceeds vacuum_cleanup_index_scale_factor fraction
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* of original tuples count.
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*/
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relopts = (StdRdOptions *) info->index->rd_options;
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cleanup_scale_factor = (relopts &&
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@ -829,7 +830,7 @@ _bt_vacuum_needs_cleanup(IndexVacuumInfo *info)
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? relopts->vacuum_cleanup_index_scale_factor
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: vacuum_cleanup_index_scale_factor;
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if (cleanup_scale_factor < 0 ||
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if (cleanup_scale_factor <= 0 ||
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metad->btm_last_cleanup_num_heap_tuples < 0 ||
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info->num_heap_tuples > (1.0 + cleanup_scale_factor) *
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metad->btm_last_cleanup_num_heap_tuples)
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@ -870,8 +871,8 @@ btbulkdelete(IndexVacuumInfo *info, IndexBulkDeleteResult *stats,
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&oldestBtpoXact);
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/*
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* Update cleanup-related information in metapage. These information
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* is used only for cleanup but keeping up them to date can avoid
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* Update cleanup-related information in metapage. This information
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* is used only for cleanup but keeping them up to date can avoid
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* unnecessary cleanup even after bulkdelete.
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*/
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_bt_update_meta_cleanup_info(info->index, oldestBtpoXact,
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@ -899,8 +900,8 @@ btvacuumcleanup(IndexVacuumInfo *info, IndexBulkDeleteResult *stats)
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* If btbulkdelete was called, we need not do anything, just return the
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* stats from the latest btbulkdelete call. If it wasn't called, we might
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* still need to do a pass over the index, to recycle any newly-recyclable
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* pages and to obtain index statistics. _bt_vacuum_needs_cleanup checks
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* is there are newly-recyclable or stalled index statistics.
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* pages or to obtain index statistics. _bt_vacuum_needs_cleanup
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* determines if either are needed.
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*
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* Since we aren't going to actually delete any leaf items, there's no
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* need to go through all the vacuum-cycle-ID pushups.
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@ -3238,7 +3238,7 @@ static struct config_real ConfigureNamesReal[] =
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},
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{
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{"vacuum_cleanup_index_scale_factor", PGC_SIGHUP, AUTOVACUUM,
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{"vacuum_cleanup_index_scale_factor", PGC_USERSET, AUTOVACUUM,
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gettext_noop("Number of tuple inserts prior to index cleanup as a fraction of reltuples."),
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NULL
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},
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@ -1855,13 +1855,15 @@ psql_completion(const char *text, int start, int end)
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COMPLETE_WITH_CONST("(");
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/* ALTER INDEX <foo> SET|RESET ( */
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else if (Matches5("ALTER", "INDEX", MatchAny, "RESET", "("))
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COMPLETE_WITH_LIST7("fillfactor", "recheck_on_update",
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COMPLETE_WITH_LIST8("fillfactor", "recheck_on_update",
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"vacuum_cleanup_index_scale_factor", /* BTREE */
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"fastupdate", "gin_pending_list_limit", /* GIN */
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"buffering", /* GiST */
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"pages_per_range", "autosummarize" /* BRIN */
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);
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else if (Matches5("ALTER", "INDEX", MatchAny, "SET", "("))
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COMPLETE_WITH_LIST7("fillfactor =", "recheck_on_update =",
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COMPLETE_WITH_LIST8("fillfactor =", "recheck_on_update =",
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"vacuum_cleanup_index_scale_factor =", /* BTREE */
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"fastupdate =", "gin_pending_list_limit =", /* GIN */
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"buffering =", /* GiST */
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"pages_per_range =", "autosummarize =" /* BRIN */
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