Add TRUNCATE parameter to VACUUM.

This commit adds new parameter to VACUUM command, TRUNCATE,
which specifies that VACUUM should attempt to truncate off
any empty pages at the end of the table and allow the disk space
for the truncated pages to be returned to the operating system.

This parameter, if specified, overrides the vacuum_truncate
reloption. If neither the reloption nor the VACUUM option is
used, the default is true, as before.

Author: Fujii Masao
Reviewed-by: Julien Rouhaud, Masahiko Sawada
Discussion: https://postgr.es/m/CAD21AoD+qtrSDL=GSma4Wd3kLYLeRC0hPna-YAdkDeV4z156vg@mail.gmail.com

1 files changed, 7 insertions, 6 deletions

diff --git a/src/backend/access/heap/vacuumlazy.c b/src/backend/access/heap/vacuumlazy.c
index 0f70dc883d1..f1a79059cdb 100644
--- a/src/backend/access/heap/vacuumlazy.c
+++ b/src/backend/access/heap/vacuumlazy.c
@@ -163,7 +163,8 @@ static void lazy_cleanup_index(Relation indrel,
 				   LVRelStats *vacrelstats);
 static int lazy_vacuum_page(Relation onerel, BlockNumber blkno, Buffer buffer,
 				 int tupindex, LVRelStats *vacrelstats, Buffer *vmbuffer);
-static bool should_attempt_truncation(Relation rel, LVRelStats *vacrelstats);
+static bool should_attempt_truncation(VacuumParams *params,
+						 LVRelStats *vacrelstats);
 static void lazy_truncate_heap(Relation onerel, LVRelStats *vacrelstats);
 static BlockNumber count_nondeletable_pages(Relation onerel,
 						 LVRelStats *vacrelstats);
@@ -210,6 +211,7 @@ heap_vacuum_rel(Relation onerel, VacuumParams *params,
 
 	Assert(params != NULL);
 	Assert(params->index_cleanup != VACOPT_TERNARY_DEFAULT);
+	Assert(params->truncate != VACOPT_TERNARY_DEFAULT);
 
 	/* not every AM requires these to be valid, but heap does */
 	Assert(TransactionIdIsNormal(onerel->rd_rel->relfrozenxid));
@@ -308,7 +310,7 @@ heap_vacuum_rel(Relation onerel, VacuumParams *params,
 	/*
 	 * Optionally truncate the relation.
 	 */
-	if (should_attempt_truncation(onerel, vacrelstats))
+	if (should_attempt_truncation(params, vacrelstats))
 		lazy_truncate_heap(onerel, vacrelstats);
 
 	/* Report that we are now doing final cleanup */
@@ -652,7 +654,7 @@ lazy_scan_heap(Relation onerel, VacuumParams *params, LVRelStats *vacrelstats,
 
 		/* see note above about forcing scanning of last page */
 #define FORCE_CHECK_PAGE() \
-		(blkno == nblocks - 1 && should_attempt_truncation(onerel, vacrelstats))
+		(blkno == nblocks - 1 && should_attempt_truncation(params, vacrelstats))
 
 		pgstat_progress_update_param(PROGRESS_VACUUM_HEAP_BLKS_SCANNED, blkno);
 
@@ -1845,12 +1847,11 @@ lazy_cleanup_index(Relation indrel,
  * careful to depend only on fields that lazy_scan_heap updates on-the-fly.
  */
 static bool
-should_attempt_truncation(Relation rel, LVRelStats *vacrelstats)
+should_attempt_truncation(VacuumParams *params, LVRelStats *vacrelstats)
 {
 	BlockNumber possibly_freeable;
 
-	if (rel->rd_options != NULL &&
-		((StdRdOptions *) rel->rd_options)->vacuum_truncate == false)
+	if (params->truncate == VACOPT_TERNARY_DISABLED)
 		return false;
 
 	possibly_freeable = vacrelstats->rel_pages - vacrelstats->nonempty_pages;