diff options
Diffstat (limited to 'src/backend/commands/vacuumlazy.c')
| -rw-r--r-- | src/backend/commands/vacuumlazy.c | 47 |
1 files changed, 28 insertions, 19 deletions
diff --git a/src/backend/commands/vacuumlazy.c b/src/backend/commands/vacuumlazy.c index 6eee5765e72..95f13a514e1 100644 --- a/src/backend/commands/vacuumlazy.c +++ b/src/backend/commands/vacuumlazy.c @@ -31,7 +31,7 @@ * * * IDENTIFICATION - * $Header: /cvsroot/pgsql/src/backend/commands/vacuumlazy.c,v 1.26 2003/02/24 00:57:17 tgl Exp $ + * $Header: /cvsroot/pgsql/src/backend/commands/vacuumlazy.c,v 1.27 2003/03/04 21:51:21 tgl Exp $ * *------------------------------------------------------------------------- */ @@ -51,21 +51,11 @@ /* * Space/time tradeoff parameters: do these need to be user-tunable? * - * A page with less than PAGE_SPACE_THRESHOLD free space will be forgotten - * immediately, and not even passed to the free space map. Removing the - * uselessly small entries early saves cycles, and in particular reduces - * the amount of time we spend holding the FSM lock when we finally call - * MultiRecordFreeSpace. Since the FSM will ignore pages below its own - * runtime threshold anyway, there's no point in making this really small. - * XXX Is it worth trying to measure average tuple size, and using that to - * set the threshold? Problem is we don't know average tuple size very - * accurately for the first few pages... - * * To consider truncating the relation, we want there to be at least - * relsize / REL_TRUNCATE_FRACTION potentially-freeable pages. + * REL_TRUNCATE_MINIMUM or (relsize / REL_TRUNCATE_FRACTION) (whichever + * is less) potentially-freeable pages. */ -#define PAGE_SPACE_THRESHOLD ((Size) (BLCKSZ / 32)) - +#define REL_TRUNCATE_MINIMUM 1000 #define REL_TRUNCATE_FRACTION 16 /* MAX_TUPLES_PER_PAGE can be a conservative upper limit */ @@ -78,6 +68,7 @@ typedef struct LVRelStats BlockNumber rel_pages; double rel_tuples; BlockNumber nonempty_pages; /* actually, last nonempty page + 1 */ + Size threshold; /* minimum interesting free space */ /* List of TIDs of tuples we intend to delete */ /* NB: this list is ordered by TID address */ int num_dead_tuples; /* current # of entries */ @@ -149,6 +140,10 @@ lazy_vacuum_rel(Relation onerel, VacuumStmt *vacstmt) vacrelstats = (LVRelStats *) palloc0(sizeof(LVRelStats)); + /* Set threshold for interesting free space = average request size */ + /* XXX should we scale it up or down? Adjust vacuum.c too, if so */ + vacrelstats->threshold = GetAvgFSMRequestSize(&onerel->rd_node); + /* Open all indexes of the relation */ vac_open_indexes(onerel, &nindexes, &Irel); hasindex = (nindexes > 0); @@ -166,7 +161,8 @@ lazy_vacuum_rel(Relation onerel, VacuumStmt *vacstmt) * number of pages. Otherwise, the time taken isn't worth it. */ possibly_freeable = vacrelstats->rel_pages - vacrelstats->nonempty_pages; - if (possibly_freeable > vacrelstats->rel_pages / REL_TRUNCATE_FRACTION) + if (possibly_freeable >= REL_TRUNCATE_MINIMUM || + possibly_freeable >= vacrelstats->rel_pages / REL_TRUNCATE_FRACTION) lazy_truncate_heap(onerel, vacrelstats); /* Update shared free space map with final free space info */ @@ -943,8 +939,21 @@ lazy_record_free_space(LVRelStats *vacrelstats, PageFreeSpaceInfo *pageSpaces; int n; - /* Ignore pages with little free space */ - if (avail < PAGE_SPACE_THRESHOLD) + /* + * A page with less than stats->threshold free space will be forgotten + * immediately, and never passed to the free space map. Removing the + * uselessly small entries early saves cycles, and in particular reduces + * the amount of time we spend holding the FSM lock when we finally call + * RecordRelationFreeSpace. Since the FSM will probably drop pages with + * little free space anyway, there's no point in making this really small. + * + * XXX Is it worth trying to measure average tuple size, and using that to + * adjust the threshold? Would be worthwhile if FSM has no stats yet + * for this relation. But changing the threshold as we scan the rel + * might lead to bizarre behavior, too. Also, it's probably better if + * vacuum.c has the same thresholding behavior as we do here. + */ + if (avail < vacrelstats->threshold) return; /* Copy pointers to local variables for notational simplicity */ @@ -1079,13 +1088,13 @@ lazy_update_fsm(Relation onerel, LVRelStats *vacrelstats) int nPages = vacrelstats->num_free_pages; /* - * Sort data into order, as required by MultiRecordFreeSpace. + * Sort data into order, as required by RecordRelationFreeSpace. */ if (nPages > 1) qsort(pageSpaces, nPages, sizeof(PageFreeSpaceInfo), vac_cmp_page_spaces); - MultiRecordFreeSpace(&onerel->rd_node, 0, nPages, pageSpaces); + RecordRelationFreeSpace(&onerel->rd_node, nPages, pageSpaces); } /* |