/*
* analyze_rel() -- analyze one relation
- *
- * If update_reltuples is true, we update reltuples and relpages columns
- * in pg_class. Caller should pass false if we're part of VACUUM ANALYZE,
- * and the VACUUM didn't skip any pages. We only have an approximate count,
- * so we don't want to overwrite the accurate values already inserted by the
- * VACUUM in that case. VACUUM always scans all indexes, however, so the
- * pg_class entries for indexes are never updated if we're part of VACUUM
- * ANALYZE.
*/
void
-analyze_rel(Oid relid, VacuumStmt *vacstmt,
- BufferAccessStrategy bstrategy, bool update_reltuples)
+analyze_rel(Oid relid, VacuumStmt *vacstmt, BufferAccessStrategy bstrategy)
{
Relation onerel;
int attr_cnt,
}
/*
- * Quit if no analyzable columns and no pg_class update needed.
+ * Quit if no analyzable columns.
*/
- if (attr_cnt <= 0 && !analyzableindex && !update_reltuples)
+ if (attr_cnt <= 0 && !analyzableindex)
goto cleanup;
/*
/*
* Update pages/tuples stats in pg_class.
*/
- if (update_reltuples)
- {
- vac_update_relstats(onerel,
- RelationGetNumberOfBlocks(onerel),
- totalrows, hasindex, InvalidTransactionId);
- /* report results to the stats collector, too */
- pgstat_report_analyze(onerel, totalrows, totaldeadrows);
- }
+ vac_update_relstats(onerel,
+ RelationGetNumberOfBlocks(onerel),
+ totalrows, hasindex, InvalidTransactionId);
+ /* report results to the stats collector, too */
+ pgstat_report_analyze(onerel, totalrows, totaldeadrows);
/*
* Same for indexes. Vacuum always scans all indexes, so if we're part of
qsort((void *) rows, numrows, sizeof(HeapTuple), compare_rows);
/*
- * Estimate total numbers of rows in relation.
+ * Estimate total numbers of rows in relation. For live rows, use
+ * vac_estimate_reltuples; for dead rows, we have no source of old
+ * information, so we have to assume the density is the same in unseen
+ * pages as in the pages we scanned.
*/
+ *totalrows = vac_estimate_reltuples(onerel, true,
+ totalblocks,
+ bs.m,
+ liverows);
if (bs.m > 0)
- {
- *totalrows = floor((liverows * totalblocks) / bs.m + 0.5);
- *totaldeadrows = floor((deadrows * totalblocks) / bs.m + 0.5);
- }
+ *totaldeadrows = floor((deadrows / bs.m) * totalblocks + 0.5);
else
- {
- *totalrows = 0.0;
*totaldeadrows = 0.0;
- }
/*
* Emit some interesting relation info
#include <sys/time.h>
#include <unistd.h>
+#include <math.h>
+
#include "access/clog.h"
#include "access/genam.h"
#include "access/heapam.h"
const char *stmttype);
static void vac_truncate_clog(TransactionId frozenXID);
static void vacuum_rel(Oid relid, VacuumStmt *vacstmt, bool do_toast,
- bool for_wraparound, bool *scanned_all);
+ bool for_wraparound);
static bool full_vacuum_rel(Relation onerel, VacuumStmt *vacstmt);
static void scan_heap(VRelStats *vacrelstats, Relation onerel,
VacPageList vacuum_pages, VacPageList fraged_pages);
foreach(cur, relations)
{
Oid relid = lfirst_oid(cur);
- bool scanned_all = false;
if (vacstmt->vacuum)
- vacuum_rel(relid, vacstmt, do_toast, for_wraparound,
- &scanned_all);
+ vacuum_rel(relid, vacstmt, do_toast, for_wraparound);
if (vacstmt->analyze)
{
else
old_context = MemoryContextSwitchTo(anl_context);
- analyze_rel(relid, vacstmt, vac_strategy, !scanned_all);
+ analyze_rel(relid, vacstmt, vac_strategy);
if (use_own_xacts)
{
}
+/*
+ * vac_estimate_reltuples() -- estimate the new value for pg_class.reltuples
+ *
+ * If we scanned the whole relation then we should just use the count of
+ * live tuples seen; but if we did not, we should not trust the count
+ * unreservedly, especially not in VACUUM, which may have scanned a quite
+ * nonrandom subset of the table. When we have only partial information,
+ * we take the old value of pg_class.reltuples as a measurement of the
+ * tuple density in the unscanned pages.
+ *
+ * This routine is shared by VACUUM and ANALYZE.
+ */
+double
+vac_estimate_reltuples(Relation relation, bool is_analyze,
+ BlockNumber total_pages,
+ BlockNumber scanned_pages,
+ double scanned_tuples)
+{
+ BlockNumber old_rel_pages = relation->rd_rel->relpages;
+ double old_rel_tuples = relation->rd_rel->reltuples;
+ double old_density;
+ double new_density;
+ double multiplier;
+ double updated_density;
+
+ /* If we did scan the whole table, just use the count as-is */
+ if (scanned_pages >= total_pages)
+ return scanned_tuples;
+
+ /*
+ * If scanned_pages is zero but total_pages isn't, keep the existing
+ * value of reltuples.
+ */
+ if (scanned_pages == 0)
+ return old_rel_tuples;
+
+ /*
+ * If old value of relpages is zero, old density is indeterminate; we
+ * can't do much except scale up scanned_tuples to match total_pages.
+ */
+ if (old_rel_pages == 0)
+ return floor((scanned_tuples / scanned_pages) * total_pages + 0.5);
+
+ /*
+ * Okay, we've covered the corner cases. The normal calculation is to
+ * convert the old measurement to a density (tuples per page), then
+ * update the density using an exponential-moving-average approach,
+ * and finally compute reltuples as updated_density * total_pages.
+ *
+ * For ANALYZE, the moving average multiplier is just the fraction of
+ * the table's pages we scanned. This is equivalent to assuming
+ * that the tuple density in the unscanned pages didn't change. Of
+ * course, it probably did, if the new density measurement is different.
+ * But over repeated cycles, the value of reltuples will converge towards
+ * the correct value, if repeated measurements show the same new density.
+ *
+ * For VACUUM, the situation is a bit different: we have looked at a
+ * nonrandom sample of pages, but we know for certain that the pages we
+ * didn't look at are precisely the ones that haven't changed lately.
+ * Thus, there is a reasonable argument for doing exactly the same thing
+ * as for the ANALYZE case, that is use the old density measurement as
+ * the value for the unscanned pages.
+ *
+ * This logic could probably use further refinement.
+ */
+ old_density = old_rel_tuples / old_rel_pages;
+ new_density = scanned_tuples / scanned_pages;
+ multiplier = (double) scanned_pages / (double) total_pages;
+ updated_density = old_density + (new_density - old_density) * multiplier;
+ return floor(updated_density * total_pages + 0.5);
+}
+
+
/*
* vac_update_relstats() -- update statistics for one relation
*
* many small transactions. Otherwise, two-phase locking would require
* us to lock the entire database during one pass of the vacuum cleaner.
*
- * We'll return true in *scanned_all if the vacuum scanned all heap
- * pages, and updated pg_class.
- *
* At entry and exit, we are not inside a transaction.
*/
static void
-vacuum_rel(Oid relid, VacuumStmt *vacstmt, bool do_toast, bool for_wraparound,
- bool *scanned_all)
+vacuum_rel(Oid relid, VacuumStmt *vacstmt, bool do_toast, bool for_wraparound)
{
LOCKMODE lmode;
Relation onerel;
int save_nestlevel;
bool heldoff;
- if (scanned_all)
- *scanned_all = false;
-
/* Begin a transaction for vacuuming this relation */
StartTransactionCommand();
if (vacstmt->full)
heldoff = full_vacuum_rel(onerel, vacstmt);
else
- heldoff = lazy_vacuum_rel(onerel, vacstmt, vac_strategy, scanned_all);
+ heldoff = lazy_vacuum_rel(onerel, vacstmt, vac_strategy);
/* Roll back any GUC changes executed by index functions */
AtEOXact_GUC(false, save_nestlevel);
* totally unimportant for toast relations.
*/
if (toast_relid != InvalidOid)
- vacuum_rel(toast_relid, vacstmt, false, for_wraparound, NULL);
+ vacuum_rel(toast_relid, vacstmt, false, for_wraparound);
/*
* Now release the session-level lock on the master table.
/* report results to the stats collector, too */
pgstat_report_vacuum(RelationGetRelid(onerel), onerel->rd_rel->relisshared,
- true, vacstmt->analyze, vacrelstats->rel_tuples);
+ vacstmt->analyze, vacrelstats->rel_tuples);
return heldoff;
}
* Before we consider skipping a page that's marked as clean in
* visibility map, we must've seen at least this many clean pages.
*/
-#define SKIP_PAGES_THRESHOLD 32
+#define SKIP_PAGES_THRESHOLD ((BlockNumber) 32)
typedef struct LVRelStats
{
/* hasindex = true means two-pass strategy; false means one-pass */
bool hasindex;
- bool scanned_all; /* have we scanned all pages (this far)? */
/* Overall statistics about rel */
- BlockNumber rel_pages;
+ BlockNumber rel_pages; /* total number of pages */
+ BlockNumber scanned_pages; /* number of pages we examined */
+ double scanned_tuples; /* counts only tuples on scanned pages */
double old_rel_tuples; /* previous value of pg_class.reltuples */
- double rel_tuples; /* counts only tuples on scanned pages */
+ double new_rel_tuples; /* new estimated total # of tuples */
BlockNumber pages_removed;
double tuples_deleted;
BlockNumber nonempty_pages; /* actually, last nonempty page + 1 */
*/
bool
lazy_vacuum_rel(Relation onerel, VacuumStmt *vacstmt,
- BufferAccessStrategy bstrategy, bool *scanned_all)
+ BufferAccessStrategy bstrategy)
{
LVRelStats *vacrelstats;
Relation *Irel;
vacrelstats = (LVRelStats *) palloc0(sizeof(LVRelStats));
- vacrelstats->scanned_all = true; /* will be cleared if we skip a page */
vacrelstats->old_rel_tuples = onerel->rd_rel->reltuples;
vacrelstats->num_index_scans = 0;
FreeSpaceMapVacuum(onerel);
/*
- * Update statistics in pg_class. But only if we didn't skip any pages;
- * the tuple count only includes tuples from the pages we've visited, and
- * we haven't frozen tuples in unvisited pages either. The page count is
- * accurate in any case, but because we use the reltuples / relpages ratio
- * in the planner, it's better to not update relpages either if we can't
- * update reltuples.
+ * Update statistics in pg_class. But don't change relfrozenxid if we
+ * skipped any pages.
*/
- if (vacrelstats->scanned_all)
- vac_update_relstats(onerel,
- vacrelstats->rel_pages, vacrelstats->rel_tuples,
- vacrelstats->hasindex,
- FreezeLimit);
+ vac_update_relstats(onerel,
+ vacrelstats->rel_pages, vacrelstats->new_rel_tuples,
+ vacrelstats->hasindex,
+ (vacrelstats->scanned_pages < vacrelstats->rel_pages) ?
+ InvalidTransactionId :
+ FreezeLimit);
/* report results to the stats collector, too */
pgstat_report_vacuum(RelationGetRelid(onerel),
onerel->rd_rel->relisshared,
- vacrelstats->scanned_all,
- vacstmt->analyze, vacrelstats->rel_tuples);
+ vacstmt->analyze,
+ vacrelstats->new_rel_tuples);
/* and log the action if appropriate */
if (IsAutoVacuumWorkerProcess() && Log_autovacuum_min_duration >= 0)
get_namespace_name(RelationGetNamespace(onerel)),
RelationGetRelationName(onerel),
vacrelstats->num_index_scans,
- vacrelstats->pages_removed, vacrelstats->rel_pages,
- vacrelstats->tuples_deleted, vacrelstats->rel_tuples,
+ vacrelstats->pages_removed,
+ vacrelstats->rel_pages,
+ vacrelstats->tuples_deleted,
+ vacrelstats->new_rel_tuples,
pg_rusage_show(&ru0))));
}
- if (scanned_all)
- *scanned_all = vacrelstats->scanned_all;
-
return heldoff;
}
HeapTupleData tuple;
char *relname;
BlockNumber empty_pages,
- scanned_pages,
vacuumed_pages;
double num_tuples,
tups_vacuumed,
int i;
PGRUsage ru0;
Buffer vmbuffer = InvalidBuffer;
- BlockNumber all_visible_streak;
+ BlockNumber next_not_all_visible_block;
+ bool skipping_all_visible_blocks;
pg_rusage_init(&ru0);
get_namespace_name(RelationGetNamespace(onerel)),
relname)));
- empty_pages = vacuumed_pages = scanned_pages = 0;
+ empty_pages = vacuumed_pages = 0;
num_tuples = tups_vacuumed = nkeep = nunused = 0;
indstats = (IndexBulkDeleteResult **)
nblocks = RelationGetNumberOfBlocks(onerel);
vacrelstats->rel_pages = nblocks;
+ vacrelstats->scanned_pages = 0;
vacrelstats->nonempty_pages = 0;
lazy_space_alloc(vacrelstats, nblocks);
- all_visible_streak = 0;
+ /*
+ * We want to skip pages that don't require vacuuming according to the
+ * visibility map, but only when we can skip at least SKIP_PAGES_THRESHOLD
+ * consecutive pages. Since we're reading sequentially, the OS should be
+ * doing readahead for us, so there's no gain in skipping a page now and
+ * then; that's likely to disable readahead and so be counterproductive.
+ * Also, skipping even a single page means that we can't update
+ * relfrozenxid, so we only want to do it if we can skip a goodly number
+ * of pages.
+ *
+ * Before entering the main loop, establish the invariant that
+ * next_not_all_visible_block is the next block number >= blkno that's
+ * not all-visible according to the visibility map, or nblocks if there's
+ * no such block. Also, we set up the skipping_all_visible_blocks flag,
+ * which is needed because we need hysteresis in the decision: once we've
+ * started skipping blocks, we may as well skip everything up to the next
+ * not-all-visible block.
+ *
+ * Note: if scan_all is true, we won't actually skip any pages; but we
+ * maintain next_not_all_visible_block anyway, so as to set up the
+ * all_visible_according_to_vm flag correctly for each page.
+ */
+ for (next_not_all_visible_block = 0;
+ next_not_all_visible_block < nblocks;
+ next_not_all_visible_block++)
+ {
+ if (!visibilitymap_test(onerel, next_not_all_visible_block, &vmbuffer))
+ break;
+ vacuum_delay_point();
+ }
+ if (next_not_all_visible_block >= SKIP_PAGES_THRESHOLD)
+ skipping_all_visible_blocks = true;
+ else
+ skipping_all_visible_blocks = false;
+
for (blkno = 0; blkno < nblocks; blkno++)
{
Buffer buf;
OffsetNumber frozen[MaxOffsetNumber];
int nfrozen;
Size freespace;
- bool all_visible_according_to_vm = false;
+ bool all_visible_according_to_vm;
bool all_visible;
bool has_dead_tuples;
- /*
- * Skip pages that don't require vacuuming according to the visibility
- * map. But only if we've seen a streak of at least
- * SKIP_PAGES_THRESHOLD pages marked as clean. Since we're reading
- * sequentially, the OS should be doing readahead for us and there's
- * no gain in skipping a page now and then. You need a longer run of
- * consecutive skipped pages before it's worthwhile. Also, skipping
- * even a single page means that we can't update relfrozenxid or
- * reltuples, so we only want to do it if there's a good chance to
- * skip a goodly number of pages.
- */
- if (!scan_all)
+ if (blkno == next_not_all_visible_block)
{
- all_visible_according_to_vm =
- visibilitymap_test(onerel, blkno, &vmbuffer);
- if (all_visible_according_to_vm)
+ /* Time to advance next_not_all_visible_block */
+ for (next_not_all_visible_block++;
+ next_not_all_visible_block < nblocks;
+ next_not_all_visible_block++)
{
- all_visible_streak++;
- if (all_visible_streak >= SKIP_PAGES_THRESHOLD)
- {
- vacrelstats->scanned_all = false;
- continue;
- }
+ if (!visibilitymap_test(onerel, next_not_all_visible_block,
+ &vmbuffer))
+ break;
+ vacuum_delay_point();
}
+
+ /*
+ * We know we can't skip the current block. But set up
+ * skipping_all_visible_blocks to do the right thing at the
+ * following blocks.
+ */
+ if (next_not_all_visible_block - blkno > SKIP_PAGES_THRESHOLD)
+ skipping_all_visible_blocks = true;
else
- all_visible_streak = 0;
+ skipping_all_visible_blocks = false;
+ all_visible_according_to_vm = false;
+ }
+ else
+ {
+ /* Current block is all-visible */
+ if (skipping_all_visible_blocks && !scan_all)
+ continue;
+ all_visible_according_to_vm = true;
}
vacuum_delay_point();
- scanned_pages++;
+ vacrelstats->scanned_pages++;
/*
* If we are close to overrunning the available space for dead-tuple
}
/* save stats for use later */
- vacrelstats->rel_tuples = num_tuples;
+ vacrelstats->scanned_tuples = num_tuples;
vacrelstats->tuples_deleted = tups_vacuumed;
+ /* now we can compute the new value for pg_class.reltuples */
+ vacrelstats->new_rel_tuples = vac_estimate_reltuples(onerel, false,
+ nblocks,
+ vacrelstats->scanned_pages,
+ num_tuples);
+
/* If any tuples need to be deleted, perform final vacuum cycle */
/* XXX put a threshold on min number of tuples here? */
if (vacrelstats->num_dead_tuples > 0)
ereport(elevel,
(errmsg("\"%s\": found %.0f removable, %.0f nonremovable row versions in %u out of %u pages",
RelationGetRelationName(onerel),
- tups_vacuumed, num_tuples, scanned_pages, nblocks),
+ tups_vacuumed, num_tuples,
+ vacrelstats->scanned_pages, nblocks),
errdetail("%.0f dead row versions cannot be removed yet.\n"
"There were %.0f unused item pointers.\n"
"%u pages are entirely empty.\n"
ivinfo.index = indrel;
ivinfo.vacuum_full = false;
ivinfo.analyze_only = false;
- ivinfo.estimated_count = !vacrelstats->scanned_all;
+ ivinfo.estimated_count = (vacrelstats->scanned_pages < vacrelstats->rel_pages);
ivinfo.message_level = elevel;
- /* use rel_tuples only if we scanned all pages, else fall back */
- ivinfo.num_heap_tuples = vacrelstats->scanned_all ? vacrelstats->rel_tuples : vacrelstats->old_rel_tuples;
+ ivinfo.num_heap_tuples = vacrelstats->new_rel_tuples;
ivinfo.strategy = vac_strategy;
stats = index_vacuum_cleanup(&ivinfo, stats);
new_rel_pages = RelationGetNumberOfBlocks(onerel);
if (new_rel_pages != old_rel_pages)
{
- /* might as well use the latest news when we update pg_class stats */
- vacrelstats->rel_pages = new_rel_pages;
+ /*
+ * Note: we intentionally don't update vacrelstats->rel_pages with
+ * the new rel size here. If we did, it would amount to assuming that
+ * the new pages are empty, which is unlikely. Leaving the numbers
+ * alone amounts to assuming that the new pages have the same tuple
+ * density as existing ones, which is less unlikely.
+ */
UnlockRelation(onerel, AccessExclusiveLock);
return;
}
* can safely access the table again.
*/
- /* update statistics */
+ /*
+ * Update statistics. Here, it *is* correct to adjust rel_pages without
+ * also touching reltuples, since the tuple count wasn't changed by the
+ * truncation.
+ */
vacrelstats->rel_pages = new_rel_pages;
vacrelstats->pages_removed = old_rel_pages - new_rel_pages;
* ---------
*/
void
-pgstat_report_vacuum(Oid tableoid, bool shared, bool scanned_all,
+pgstat_report_vacuum(Oid tableoid, bool shared,
bool analyze, PgStat_Counter tuples)
{
PgStat_MsgVacuum msg;
pgstat_setheader(&msg.m_hdr, PGSTAT_MTYPE_VACUUM);
msg.m_databaseid = shared ? InvalidOid : MyDatabaseId;
msg.m_tableoid = tableoid;
- msg.m_scanned_all = scanned_all;
msg.m_analyze = analyze;
msg.m_autovacuum = IsAutoVacuumWorkerProcess(); /* is this autovacuum? */
msg.m_vacuumtime = GetCurrentTimestamp();
tabentry->autovac_vacuum_timestamp = msg->m_vacuumtime;
else
tabentry->vacuum_timestamp = msg->m_vacuumtime;
- if (msg->m_scanned_all)
- tabentry->n_live_tuples = msg->m_tuples;
+ tabentry->n_live_tuples = msg->m_tuples;
/* Resetting dead_tuples to 0 is an approximation ... */
tabentry->n_dead_tuples = 0;
if (msg->m_analyze)
{
- if (msg->m_scanned_all)
- tabentry->last_anl_tuples = msg->m_tuples;
- else
- {
- /* last_anl_tuples must never exceed n_live_tuples+n_dead_tuples */
- tabentry->last_anl_tuples = Min(tabentry->last_anl_tuples,
- tabentry->n_live_tuples);
- }
-
+ tabentry->last_anl_tuples = msg->m_tuples;
if (msg->m_autovacuum)
tabentry->autovac_analyze_timestamp = msg->m_vacuumtime;
else
extern void vac_open_indexes(Relation relation, LOCKMODE lockmode,
int *nindexes, Relation **Irel);
extern void vac_close_indexes(int nindexes, Relation *Irel, LOCKMODE lockmode);
+extern double vac_estimate_reltuples(Relation relation, bool is_analyze,
+ BlockNumber total_pages,
+ BlockNumber scanned_pages,
+ double scanned_tuples);
extern void vac_update_relstats(Relation relation,
BlockNumber num_pages,
double num_tuples,
/* in commands/vacuumlazy.c */
extern bool lazy_vacuum_rel(Relation onerel, VacuumStmt *vacstmt,
- BufferAccessStrategy bstrategy, bool *scanned_all);
+ BufferAccessStrategy bstrategy);
/* in commands/analyze.c */
extern void analyze_rel(Oid relid, VacuumStmt *vacstmt,
- BufferAccessStrategy bstrategy, bool update_reltuples);
+ BufferAccessStrategy bstrategy);
#endif /* VACUUM_H */
Oid m_tableoid;
bool m_analyze;
bool m_autovacuum;
- bool m_scanned_all;
TimestampTz m_vacuumtime;
PgStat_Counter m_tuples;
} PgStat_MsgVacuum;
extern void pgstat_reset_counters(void);
extern void pgstat_report_autovac(Oid dboid);
-extern void pgstat_report_vacuum(Oid tableoid, bool shared, bool scanned_all,
+extern void pgstat_report_vacuum(Oid tableoid, bool shared,
bool analyze, PgStat_Counter tuples);
extern void pgstat_report_analyze(Relation rel,
PgStat_Counter livetuples,
projects / thirdparty / postgresql.git / commitdiff
