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Reimplement free-space-map management as per recent discussions.

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Adjustable threshold is gone in favor of keeping track of total requested
page storage and doling out proportional fractions to each relation
(with a minimum amount per relation, and some quantization of the results
to avoid thrashing with small changes in page counts).  Provide special-
case code for indexes so as not to waste space storing useless page
free space counts.  Restructure internal data storage to be a flat array
instead of list-of-chunks; this may cost a little more work in data
copying when reorganizing, but allows binary search to be used during
lookup_fsm_page_entry().
This commit is contained in:
Tom Lane
2003-03-04 21:51:22 +00:00
parent a455c94257
commit 391eb5e5b6
10 changed files with 1165 additions and 741 deletions
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42
src/backend/commands/vacuum.c
View File

@@ -13,7 +13,7 @@
*
*
* IDENTIFICATION
* $Header: /cvsroot/pgsql/src/backend/commands/vacuum.c,v 1.250 2003/02/24 00:57:17 tgl Exp $
* $Header: /cvsroot/pgsql/src/backend/commands/vacuum.c,v 1.251 2003/03/04 21:51:20 tgl Exp $
*
*-------------------------------------------------------------------------
*/
@@ -336,6 +336,13 @@ vacuum(VacuumStmt *vacstmt)
*/
StartTransactionCommand(true);
/*
* If it was a database-wide VACUUM, print FSM usage statistics
* (we don't make you be superuser to see these).
*/
if (vacstmt->relation == NULL)
PrintFreeSpaceMapStatistics(elevel);
/*
* If we completed a database-wide VACUUM without skipping any
* relations, update the database's pg_database row with info
@@ -2781,31 +2788,48 @@ vac_update_fsm(Relation onerel, VacPageList fraged_pages,
BlockNumber rel_pages)
{
int nPages = fraged_pages->num_pages;
int i;
VacPage *pagedesc = fraged_pages->pagedesc;
Size threshold;
PageFreeSpaceInfo *pageSpaces;
int outPages;
int i;
/*
* We only report pages with free space at least equal to the average
* request size --- this avoids cluttering FSM with uselessly-small bits
* of space. Although FSM would discard pages with little free space
* anyway, it's important to do this prefiltering because (a) it reduces
* the time spent holding the FSM lock in RecordRelationFreeSpace, and
* (b) FSM uses the number of pages reported as a statistic for guiding
* space management. If we didn't threshold our reports the same way
* vacuumlazy.c does, we'd be skewing that statistic.
*/
threshold = GetAvgFSMRequestSize(&onerel->rd_node);
/* +1 to avoid palloc(0) */
pageSpaces = (PageFreeSpaceInfo *)
palloc((nPages + 1) * sizeof(PageFreeSpaceInfo));
outPages = 0;
for (i = 0; i < nPages; i++)
{
pageSpaces[i].blkno = fraged_pages->pagedesc[i]->blkno;
pageSpaces[i].avail = fraged_pages->pagedesc[i]->free;
/*
* fraged_pages may contain entries for pages that we later
* decided to truncate from the relation; don't enter them into
* the free space map!
*/
if (pageSpaces[i].blkno >= rel_pages)
{
nPages = i;
if (pagedesc[i]->blkno >= rel_pages)
break;
if (pagedesc[i]->free >= threshold)
{
pageSpaces[outPages].blkno = pagedesc[i]->blkno;
pageSpaces[outPages].avail = pagedesc[i]->free;
outPages++;
}
}
MultiRecordFreeSpace(&onerel->rd_node, 0, nPages, pageSpaces);
RecordRelationFreeSpace(&onerel->rd_node, outPages, pageSpaces);
pfree(pageSpaces);
}

47
src/backend/commands/vacuumlazy.c
View File

@@ -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);
}
/*