Increase upper limit for vacuum_cleanup_index_scale_factor

Upper limits for vacuum_cleanup_index_scale_factor GUC and reloption
were initially set to 100.0 in 857f9c36.  However, after further
discussion, it appears that some users like to disable B-tree cleanup
index scan completely (assuming there are no deleted pages).

vacuum_cleanup_index_scale_factor is used barely to protect against
stalled index statistics.  And after detailed consideration it appears
that risk of stalled index statistics is low.  And it would be nice to
allow advanced users setting higher values of
vacuum_cleanup_index_scale_factor.  So, set upper limit for these
GUC and reloption to DBL_MAX.

Author: Alexander Korotkov
Reviewed-by: Masahiko Sawada
Discussion: https://postgr.es/m/CAC8Q8tJCb%3DgxhzcV7T6ctx7PY-Ux1oA-AsTJc6cAVNsQiYcCzA%40mail.gmail.com

doc/src/sgml/config.sgml

@@ -6989,7 +6989,7 @@ COPY postgres_log FROM '/full/path/to/logfile.csv' WITH csv;
        </para>
 
        <para>
-        The value can range from <literal>0</literal> to <literal>100</literal>.
+        The value should be non-negative.
         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>.

src/backend/access/common/reloptions.c

@@ -416,7 +416,7 @@ static relopt_real realRelOpts[] =
 			RELOPT_KIND_BTREE,
 			ShareUpdateExclusiveLock
 		},
-		-1, 0.0, 100.0
+		-1, 0.0, DBL_MAX
 	},
 	/* list terminator */
 	{{NULL}}

src/backend/access/nbtree/nbtree.c

@@ -816,6 +816,7 @@ _bt_vacuum_needs_cleanup(IndexVacuumInfo *info)
 	{
 		StdRdOptions *relopts;
 		float8		cleanup_scale_factor;
+		float8		prev_num_heap_tuples;
 
 		/*
 		 * If table receives enough insertions and no cleanup was performed,
@@ -829,11 +830,12 @@ _bt_vacuum_needs_cleanup(IndexVacuumInfo *info)
 								relopts->vacuum_cleanup_index_scale_factor >= 0)
 			? relopts->vacuum_cleanup_index_scale_factor
 			: vacuum_cleanup_index_scale_factor;
+		prev_num_heap_tuples = metad->btm_last_cleanup_num_heap_tuples;
 
 		if (cleanup_scale_factor <= 0 ||
-			metad->btm_last_cleanup_num_heap_tuples < 0 ||
-			info->num_heap_tuples > (1.0 + cleanup_scale_factor) *
-			metad->btm_last_cleanup_num_heap_tuples)
+			prev_num_heap_tuples < 0 ||
+			(info->num_heap_tuples - prev_num_heap_tuples) /
+			prev_num_heap_tuples >= cleanup_scale_factor)
 			result = true;
 	}
 

src/backend/utils/misc/guc.c

@@ -3253,7 +3253,7 @@ static struct config_real ConfigureNamesReal[] =
 			NULL
 		},
 		&vacuum_cleanup_index_scale_factor,
-		0.1, 0.0, 100.0,
+		0.1, 0.0, DBL_MAX,
 		NULL, NULL, NULL
 	},
 

src/test/regress/expected/btree_index.out

@@ -165,7 +165,7 @@ 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);
 ERROR:  value -10.0 out of bounds for option "vacuum_cleanup_index_scale_factor"
-DETAIL:  Valid values are between "0.000000" and "100.000000".
+DETAIL:  Valid values are between "0.000000" and "179769313486231570814527423731704356798070567525844996598917476803157260780028538760589558632766878171540458953514382464234321326889464182768467546703537516986049910576551282076245490090389328944075868508455133942304583236903222948165808559332123348274797826204144723168738177180919299881250404026184124858368.000000".
 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