Separate multixact freezing parameters from xid's

Previously we were piggybacking on transaction ID parameters to freeze
multixacts; but since there isn't necessarily any relationship between
rates of Xid and multixact consumption, this turns out not to be a good
idea.

Therefore, we now have multixact-specific freezing parameters:

vacuum_multixact_freeze_min_age: when to remove multis as we come across
them in vacuum (default to 5 million, i.e. early in comparison to Xid's
default of 50 million)

vacuum_multixact_freeze_table_age: when to force whole-table scans
instead of scanning only the pages marked as not all visible in
visibility map (default to 150 million, same as for Xids).  Whichever of
both which reaches the 150 million mark earlier will cause a whole-table
scan.

autovacuum_multixact_freeze_max_age: when for cause emergency,
uninterruptible whole-table scans (default to 400 million, double as
that for Xids).  This means there shouldn't be more frequent emergency
vacuuming than previously, unless multixacts are being used very
rapidly.

Backpatch to 9.3 where multixacts were made to persist enough to require
freezing.  To avoid an ABI break in 9.3, VacuumStmt has a couple of
fields in an unnatural place, and StdRdOptions is split in two so that
the newly added fields can go at the end.

Patch by me, reviewed by Robert Haas, with additional input from Andres
Freund and Tom Lane.

4 files changed, 12 insertions, 0 deletions

diff --git a/src/include/commands/vacuum.h b/src/include/commands/vacuum.h
index 7c368905393..70350e02cb2 100644
--- a/src/include/commands/vacuum.h
+++ b/src/include/commands/vacuum.h
@@ -136,6 +136,8 @@ extern PGDLLIMPORT int default_statistics_target;		/* PGDLLIMPORT for
 														 * PostGIS */
 extern int	vacuum_freeze_min_age;
 extern int	vacuum_freeze_table_age;
+extern int	vacuum_multixact_freeze_min_age;
+extern int	vacuum_multixact_freeze_table_age;
 
 
 /* in commands/vacuum.c */
@@ -156,6 +158,8 @@ extern void vac_update_relstats(Relation relation,
 					TransactionId frozenxid,
 					MultiXactId minmulti);
 extern void vacuum_set_xid_limits(int freeze_min_age, int freeze_table_age,
+					  int multixact_freeze_min_age,
+					  int multixact_freeze_table_age,
 					  bool sharedRel,
 					  TransactionId *oldestXmin,
 					  TransactionId *freezeLimit,
diff --git a/src/include/nodes/parsenodes.h b/src/include/nodes/parsenodes.h
index ad58b3949b6..f649ad4aa07 100644
--- a/src/include/nodes/parsenodes.h
+++ b/src/include/nodes/parsenodes.h
@@ -2533,6 +2533,10 @@ typedef struct VacuumStmt
 	int			options;		/* OR of VacuumOption flags */
 	int			freeze_min_age; /* min freeze age, or -1 to use default */
 	int			freeze_table_age;		/* age at which to scan whole table */
+	int			multixact_freeze_min_age;		/* min multixact freeze age,
+												 * or -1 to use default */
+	int			multixact_freeze_table_age;		/* multixact age at which to
+												 * scan whole table */
 	RangeVar   *relation;		/* single table to process, or NULL */
 	List	   *va_cols;		/* list of column names, or NIL for all */
 } VacuumStmt;
diff --git a/src/include/postmaster/autovacuum.h b/src/include/postmaster/autovacuum.h
index 543445cc2cb..a43fcb11d1c 100644
--- a/src/include/postmaster/autovacuum.h
+++ b/src/include/postmaster/autovacuum.h
@@ -25,6 +25,7 @@ extern double autovacuum_vac_scale;
 extern int	autovacuum_anl_thresh;
 extern double autovacuum_anl_scale;
 extern int	autovacuum_freeze_max_age;
+extern int	autovacuum_multixact_freeze_max_age;
 extern int	autovacuum_vac_cost_delay;
 extern int	autovacuum_vac_cost_limit;
 
diff --git a/src/include/utils/rel.h b/src/include/utils/rel.h
index 9b8a4c9aa50..c87dadc0ebd 100644
--- a/src/include/utils/rel.h
+++ b/src/include/utils/rel.h
@@ -206,6 +206,9 @@ typedef struct AutoVacOpts
 	int			freeze_min_age;
 	int			freeze_max_age;
 	int			freeze_table_age;
+	int			multixact_freeze_min_age;
+	int			multixact_freeze_max_age;
+	int			multixact_freeze_table_age;
 	float8		vacuum_scale_factor;
 	float8		analyze_scale_factor;
 } AutoVacOpts;