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

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

2 files changed, 48 insertions, 0 deletions

diff --git a/src/test/regress/expected/btree_index.out b/src/test/regress/expected/btree_index.out
index 755cd177925..4778ac14a4c 100644
--- a/src/test/regress/expected/btree_index.out
+++ b/src/test/regress/expected/btree_index.out
@@ -150,3 +150,32 @@ vacuum btree_tall_tbl;
 -- need to insert some rows to cause the fast root page to split.
 insert into btree_tall_tbl (id, t)
   select g, repeat('x', 100) from generate_series(1, 500) g;
+--
+-- Test vacuum_cleanup_index_scale_factor
+--
+-- Simple create
+create table btree_test(a int);
+create index btree_idx1 on btree_test(a) with (vacuum_cleanup_index_scale_factor = 40.0);
+select reloptions from pg_class WHERE oid = 'btree_idx1'::regclass;
+                reloptions                
+------------------------------------------
+ {vacuum_cleanup_index_scale_factor=40.0}
+(1 row)
+
+-- Fail while setting improper values
+create index btree_idx_err on btree_test(a) with (vacuum_cleanup_index_scale_factor = -10.0);
+ERROR:  value -10.0 out of bounds for option "vacuum_cleanup_index_scale_factor"
+DETAIL:  Valid values are between "0.000000" and "100.000000".
+create index btree_idx_err on btree_test(a) with (vacuum_cleanup_index_scale_factor = 100.0);
+create index btree_idx_err on btree_test(a) with (vacuum_cleanup_index_scale_factor = 'string');
+ERROR:  invalid value for floating point option "vacuum_cleanup_index_scale_factor": string
+create index btree_idx_err on btree_test(a) with (vacuum_cleanup_index_scale_factor = true);
+ERROR:  invalid value for floating point option "vacuum_cleanup_index_scale_factor": true
+-- Simple ALTER INDEX
+alter index btree_idx1 set (vacuum_cleanup_index_scale_factor = 70.0);
+select reloptions from pg_class WHERE oid = 'btree_idx1'::regclass;
+                reloptions                
+------------------------------------------
+ {vacuum_cleanup_index_scale_factor=70.0}
+(1 row)
+
diff --git a/src/test/regress/sql/btree_index.sql b/src/test/regress/sql/btree_index.sql
index 65b08c82824..21171f77625 100644
--- a/src/test/regress/sql/btree_index.sql
+++ b/src/test/regress/sql/btree_index.sql
@@ -92,3 +92,22 @@ vacuum btree_tall_tbl;
 -- need to insert some rows to cause the fast root page to split.
 insert into btree_tall_tbl (id, t)
   select g, repeat('x', 100) from generate_series(1, 500) g;
+
+--
+-- Test vacuum_cleanup_index_scale_factor
+--
+
+-- Simple create
+create table btree_test(a int);
+create index btree_idx1 on btree_test(a) with (vacuum_cleanup_index_scale_factor = 40.0);
+select reloptions from pg_class WHERE oid = 'btree_idx1'::regclass;
+
+-- Fail while setting improper values
+create index btree_idx_err on btree_test(a) with (vacuum_cleanup_index_scale_factor = -10.0);
+create index btree_idx_err on btree_test(a) with (vacuum_cleanup_index_scale_factor = 100.0);
+create index btree_idx_err on btree_test(a) with (vacuum_cleanup_index_scale_factor = 'string');
+create index btree_idx_err on btree_test(a) with (vacuum_cleanup_index_scale_factor = true);
+
+-- Simple ALTER INDEX
+alter index btree_idx1 set (vacuum_cleanup_index_scale_factor = 70.0);
+select reloptions from pg_class WHERE oid = 'btree_idx1'::regclass;