Fix full-table-vacuum request mechanism for MultiXactIds

While autovacuum dutifully launched anti-multixact-wraparound vacuums
when the multixact "age" was reached, the vacuum code was not aware that
it needed to make them be full table vacuums.  As the resulting
partial-table vacuums aren't capable of actually increasing relminmxid,
autovacuum continued to launch anti-wraparound vacuums that didn't have
the intended effect, until age of relfrozenxid caused the vacuum to
finally be a full table one via vacuum_freeze_table_age.

To fix, introduce logic for multixacts similar to that for plain
TransactionIds, using the same GUCs.

Backpatch to 9.3, where permanent MultiXactIds were introduced.

Andres Freund, some cleanup by Álvaro

1 files changed, 14 insertions, 4 deletions

diff --git a/src/backend/commands/vacuumlazy.c b/src/backend/commands/vacuumlazy.c
index 93ea0851242..ff6bd8e5b06 100644
--- a/src/backend/commands/vacuumlazy.c
+++ b/src/backend/commands/vacuumlazy.c
@@ -180,7 +180,8 @@ lazy_vacuum_rel(Relation onerel, VacuumStmt *vacstmt,
 				write_rate;
 	bool		scan_all;		/* should we scan all pages? */
 	bool		scanned_all;	/* did we actually scan all pages? */
-	TransactionId freezeTableLimit;
+	TransactionId xidFullScanLimit;
+	MultiXactId mxactFullScanLimit;
 	BlockNumber new_rel_pages;
 	double		new_rel_tuples;
 	BlockNumber new_rel_allvisible;
@@ -203,10 +204,19 @@ lazy_vacuum_rel(Relation onerel, VacuumStmt *vacstmt,
 
 	vacuum_set_xid_limits(vacstmt->freeze_min_age, vacstmt->freeze_table_age,
 						  onerel->rd_rel->relisshared,
-						  &OldestXmin, &FreezeLimit, &freezeTableLimit,
-						  &MultiXactCutoff);
+						  &OldestXmin, &FreezeLimit, &xidFullScanLimit,
+						  &MultiXactCutoff, &mxactFullScanLimit);
+
+	/*
+	 * We request a full scan if either the table's frozen Xid is now older
+	 * than or equal to the requested Xid full-table scan limit; or if the
+	 * table's minimum MultiXactId is older than or equal to the requested mxid
+	 * full-table scan limit.
+	 */
 	scan_all = TransactionIdPrecedesOrEquals(onerel->rd_rel->relfrozenxid,
-											 freezeTableLimit);
+											 xidFullScanLimit);
+	scan_all |= MultiXactIdPrecedesOrEquals(onerel->rd_rel->relminmxid,
+											mxactFullScanLimit);
 
 	vacrelstats = (LVRelStats *) palloc0(sizeof(LVRelStats));