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Skip full index scan during cleanup of B-tree indexes when possible

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Vacuum of index consists from two stages: multiple (zero of more) ambulkdelete
calls and one amvacuumcleanup call. When workload on particular table
is append-only, then autovacuum isn't intended to touch this table. However,
user may run vacuum manually in order to fill visibility map and get benefits
of index-only scans. Then ambulkdelete wouldn't be called for indexes
of such table (because no heap tuples were deleted), only amvacuumcleanup would
be called In this case, amvacuumcleanup would perform full index scan for
two objectives: put recyclable pages into free space map and update index
statistics.

This patch allows btvacuumclanup to skip full index scan when two conditions
are satisfied: no pages are going to be put into free space map and index
statistics isn't stalled. In order to check first condition, we store
oldest btpo_xact in the meta-page. When it's precedes RecentGlobalXmin, then
there are some recyclable pages. In order to check second condition we store
number of heap tuples observed during previous full index scan by cleanup.
If fraction of newly inserted tuples is less than
vacuum_cleanup_index_scale_factor, then statistics isn't considered to be
stalled. vacuum_cleanup_index_scale_factor can be defined as both reloption and GUC (default).

This patch bumps B-tree meta-page version. Upgrade of meta-page is performed
"on the fly": during VACUUM meta-page is rewritten with new version. No special
handling in pg_upgrade is required.

Author: Masahiko Sawada, Alexander Korotkov
Review by: Peter Geoghegan, Kyotaro Horiguchi, Alexander Korotkov, Yura Sokolov
Discussion: https://www.postgresql.org/message-id/flat/CAD21AoAX+d2oD_nrd9O2YkpzHaFr=uQeGr9s1rKC3O4ENc568g@mail.gmail.com
This commit is contained in:
Teodor Sigaev
2018-04-04 19:29:00 +03:00
parent eac93e20af
commit 857f9c36cd
23 changed files with 458 additions and 45 deletions
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4
src/include/access/nbtxlog.h
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@ -38,6 +38,8 @@
* vacuum */
#define XLOG_BTREE_REUSE_PAGE 0xD0 /* old page is about to be reused from
* FSM */
#define XLOG_BTREE_META_CLEANUP 0xE0 /* update cleanup-related data in the
* metapage */
/*
* All that we need to regenerate the meta-data page
@ -48,6 +50,8 @@ typedef struct xl_btree_metadata
uint32 level;
BlockNumber fastroot;
uint32 fastlevel;
TransactionId oldest_btpo_xact;
double last_cleanup_num_heap_tuples;
} xl_btree_metadata;
/*