Allow vacuum command to process indexes in parallel.

This feature allows the vacuum to leverage multiple CPUs in order to
process indexes.  This enables us to perform index vacuuming and index
cleanup with background workers.  This adds a PARALLEL option to VACUUM
command where the user can specify the number of workers that can be used
to perform the command which is limited by the number of indexes on a
table.  Specifying zero as a number of workers will disable parallelism.
This option can't be used with the FULL option.

Each index is processed by at most one vacuum process.  Therefore parallel
vacuum can be used when the table has at least two indexes.

The parallel degree is either specified by the user or determined based on
the number of indexes that the table has, and further limited by
max_parallel_maintenance_workers.  The index can participate in parallel
vacuum iff it's size is greater than min_parallel_index_scan_size.

Author: Masahiko Sawada and Amit Kapila
Reviewed-by: Dilip Kumar, Amit Kapila, Robert Haas, Tomas Vondra,
Mahendra Singh and Sergei Kornilov
Tested-by: Mahendra Singh and Prabhat Sahu
Discussion:
https://postgr.es/m/CAD21AoDTPMgzSkV4E3SFo1CH_x50bf5PqZFQf4jmqjk-C03BWg@mail.gmail.com
https://postgr.es/m/CAA4eK1J-VoR9gzS5E75pcD-OH0mEyCdp8RihcwKrcuw7J-Q0+w@mail.gmail.com

3 files changed, 18 insertions, 1 deletions

diff --git a/src/include/access/heapam.h b/src/include/access/heapam.h
index 580b4caef7f..00a17f5f717 100644
--- a/src/include/access/heapam.h
+++ b/src/include/access/heapam.h
@@ -23,7 +23,9 @@
 #include "nodes/lockoptions.h"
 #include "nodes/primnodes.h"
 #include "storage/bufpage.h"
+#include "storage/dsm.h"
 #include "storage/lockdefs.h"
+#include "storage/shm_toc.h"
 #include "utils/relcache.h"
 #include "utils/snapshot.h"
 
@@ -193,6 +195,7 @@ extern Size SyncScanShmemSize(void);
 struct VacuumParams;
 extern void heap_vacuum_rel(Relation onerel,
 							struct VacuumParams *params, BufferAccessStrategy bstrategy);
+extern void parallel_vacuum_main(dsm_segment *seg, shm_toc *toc);
 
 /* in heap/heapam_visibility.c */
 extern bool HeapTupleSatisfiesVisibility(HeapTuple stup, Snapshot snapshot,
diff --git a/src/include/access/parallel.h b/src/include/access/parallel.h
index 646708ba5fb..fc6a5603bb6 100644
--- a/src/include/access/parallel.h
+++ b/src/include/access/parallel.h
@@ -33,7 +33,8 @@ typedef struct ParallelContext
 {
 	dlist_node	node;
 	SubTransactionId subid;
-	int			nworkers;
+	int			nworkers;		/* Maximum number of workers to launch */
+	int			nworkers_to_launch; /* Actual number of workers to launch */
 	int			nworkers_launched;
 	char	   *library_name;
 	char	   *function_name;
@@ -63,6 +64,7 @@ extern ParallelContext *CreateParallelContext(const char *library_name,
 											  const char *function_name, int nworkers);
 extern void InitializeParallelDSM(ParallelContext *pcxt);
 extern void ReinitializeParallelDSM(ParallelContext *pcxt);
+extern void ReinitializeParallelWorkers(ParallelContext *pcxt, int nworkers_to_launch);
 extern void LaunchParallelWorkers(ParallelContext *pcxt);
 extern void WaitForParallelWorkersToAttach(ParallelContext *pcxt);
 extern void WaitForParallelWorkersToFinish(ParallelContext *pcxt);
diff --git a/src/include/commands/vacuum.h b/src/include/commands/vacuum.h
index b3351ad4062..c27d255d8da 100644
--- a/src/include/commands/vacuum.h
+++ b/src/include/commands/vacuum.h
@@ -222,6 +222,13 @@ typedef struct VacuumParams
 										 * default value depends on reloptions */
 	VacOptTernaryValue truncate;	/* Truncate empty pages at the end,
 									 * default value depends on reloptions */
+
+	/*
+	 * The number of parallel vacuum workers.  0 by default which means choose
+	 * based on the number of indexes.  -1 indicates a parallel vacuum is
+	 * disabled.
+	 */
+	int			nworkers;
 } VacuumParams;
 
 /* GUC parameters */
@@ -231,6 +238,11 @@ extern int	vacuum_freeze_table_age;
 extern int	vacuum_multixact_freeze_min_age;
 extern int	vacuum_multixact_freeze_table_age;
 
+/* Variables for cost-based parallel vacuum */
+extern pg_atomic_uint32 *VacuumSharedCostBalance;
+extern pg_atomic_uint32 *VacuumActiveNWorkers;
+extern int	VacuumCostBalanceLocal;
+
 
 /* in commands/vacuum.c */
 extern void ExecVacuum(ParseState *pstate, VacuumStmt *vacstmt, bool isTopLevel);