#include "commands/vacuum.h"
#include "miscadmin.h"
#include "pgstat.h"
+#include "portability/instr_time.h"
#include "postmaster/autovacuum.h"
#include "storage/bufmgr.h"
#include "storage/freespace.h"
#define REL_TRUNCATE_MINIMUM 1000
#define REL_TRUNCATE_FRACTION 16
+/*
+ * Timing parameters for truncate locking heuristics.
+ *
+ * These were not exposed as user tunable GUC values because it didn't seem
+ * that the potential for improvement was great enough to merit the cost of
+ * supporting them.
+ */
+#define AUTOVACUUM_TRUNCATE_LOCK_CHECK_INTERVAL 20 /* ms */
+#define AUTOVACUUM_TRUNCATE_LOCK_WAIT_INTERVAL 50 /* ms */
+#define AUTOVACUUM_TRUNCATE_LOCK_TIMEOUT 5000 /* ms */
+
/*
* Guesstimation of number of dead tuples per page. This is used to
* provide an upper limit to memory allocated when vacuuming small
ItemPointer dead_tuples; /* array of ItemPointerData */
int num_index_scans;
TransactionId latestRemovedXid;
+ bool lock_waiter_detected;
} LVRelStats;
vacrelstats->old_rel_pages = onerel->rd_rel->relpages;
vacrelstats->old_rel_tuples = onerel->rd_rel->reltuples;
vacrelstats->num_index_scans = 0;
+ vacrelstats->pages_removed = 0;
+ vacrelstats->lock_waiter_detected = false;
/* Open all indexes of the relation */
vac_open_indexes(onerel, RowExclusiveLock, &nindexes, &Irel);
vacrelstats->hasindex,
new_frozen_xid);
- /* report results to the stats collector, too */
- pgstat_report_vacuum(RelationGetRelid(onerel),
- onerel->rd_rel->relisshared,
- new_rel_tuples);
+ /*
+ * Report results to the stats collector, too. An early terminated
+ * lazy_truncate_heap attempt suppresses the message and also cancels the
+ * execution of ANALYZE, if that was ordered.
+ */
+ if (!vacrelstats->lock_waiter_detected)
+ pgstat_report_vacuum(RelationGetRelid(onerel),
+ onerel->rd_rel->relisshared,
+ new_rel_tuples);
+ else
+ vacstmt->options &= ~VACOPT_ANALYZE;
/* and log the action if appropriate */
if (IsAutoVacuumWorkerProcess() && Log_autovacuum_min_duration >= 0)
BlockNumber old_rel_pages = vacrelstats->rel_pages;
BlockNumber new_rel_pages;
PGRUsage ru0;
+ int lock_retry;
pg_rusage_init(&ru0);
/*
- * We need full exclusive lock on the relation in order to do truncation.
- * If we can't get it, give up rather than waiting --- we don't want to
- * block other backends, and we don't want to deadlock (which is quite
- * possible considering we already hold a lower-grade lock).
- */
- if (!ConditionalLockRelation(onerel, AccessExclusiveLock))
- return;
-
- /*
- * Now that we have exclusive lock, look to see if the rel has grown
- * whilst we were vacuuming with non-exclusive lock. If so, give up; the
- * newly added pages presumably contain non-deletable tuples.
+ * Loop until no more truncating can be done.
*/
- new_rel_pages = RelationGetNumberOfBlocks(onerel);
- if (new_rel_pages != old_rel_pages)
+ do
{
/*
- * 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.
+ * We need full exclusive lock on the relation in order to do
+ * truncation. If we can't get it, give up rather than waiting --- we
+ * don't want to block other backends, and we don't want to deadlock
+ * (which is quite possible considering we already hold a lower-grade
+ * lock).
*/
- UnlockRelation(onerel, AccessExclusiveLock);
- return;
- }
+ vacrelstats->lock_waiter_detected = false;
+ lock_retry = 0;
+ while (true)
+ {
+ if (ConditionalLockRelation(onerel, AccessExclusiveLock))
+ break;
- /*
- * Scan backwards from the end to verify that the end pages actually
- * contain no tuples. This is *necessary*, not optional, because other
- * backends could have added tuples to these pages whilst we were
- * vacuuming.
- */
- new_rel_pages = count_nondeletable_pages(onerel, vacrelstats);
+ /*
+ * Check for interrupts while trying to (re-)acquire the exclusive
+ * lock.
+ */
+ CHECK_FOR_INTERRUPTS();
- if (new_rel_pages >= old_rel_pages)
- {
- /* can't do anything after all */
- UnlockRelation(onerel, AccessExclusiveLock);
- return;
- }
+ if (++lock_retry > (AUTOVACUUM_TRUNCATE_LOCK_TIMEOUT /
+ AUTOVACUUM_TRUNCATE_LOCK_WAIT_INTERVAL))
+ {
+ /*
+ * We failed to establish the lock in the specified number of
+ * retries. This means we give up truncating. Suppress the
+ * ANALYZE step. Doing an ANALYZE at this point will reset the
+ * dead_tuple_count in the stats collector, so we will not get
+ * called by the autovacuum launcher again to do the truncate.
+ */
+ vacrelstats->lock_waiter_detected = true;
+ ereport(LOG,
+ (errmsg("automatic vacuum of table \"%s.%s.%s\": "
+ "cannot (re)acquire exclusive "
+ "lock for truncate scan",
+ get_database_name(MyDatabaseId),
+ get_namespace_name(RelationGetNamespace(onerel)),
+ RelationGetRelationName(onerel))));
+ return;
+ }
- /*
- * Okay to truncate.
- */
- RelationTruncate(onerel, new_rel_pages);
+ pg_usleep(AUTOVACUUM_TRUNCATE_LOCK_WAIT_INTERVAL);
+ }
- /*
- * We can release the exclusive lock as soon as we have truncated. Other
- * backends can't safely access the relation until they have processed the
- * smgr invalidation that smgrtruncate sent out ... but that should happen
- * as part of standard invalidation processing once they acquire lock on
- * the relation.
- */
- UnlockRelation(onerel, AccessExclusiveLock);
+ /*
+ * Now that we have exclusive lock, look to see if the rel has grown
+ * whilst we were vacuuming with non-exclusive lock. If so, give up;
+ * the newly added pages presumably contain non-deletable tuples.
+ */
+ new_rel_pages = RelationGetNumberOfBlocks(onerel);
+ if (new_rel_pages != old_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;
+ }
- /*
- * 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;
+ /*
+ * Scan backwards from the end to verify that the end pages actually
+ * contain no tuples. This is *necessary*, not optional, because
+ * other backends could have added tuples to these pages whilst we
+ * were vacuuming.
+ */
+ new_rel_pages = count_nondeletable_pages(onerel, vacrelstats);
- ereport(elevel,
- (errmsg("\"%s\": truncated %u to %u pages",
- RelationGetRelationName(onerel),
- old_rel_pages, new_rel_pages),
- errdetail("%s.",
- pg_rusage_show(&ru0))));
+ if (new_rel_pages >= old_rel_pages)
+ {
+ /* can't do anything after all */
+ UnlockRelation(onerel, AccessExclusiveLock);
+ return;
+ }
+
+ /*
+ * Okay to truncate.
+ */
+ RelationTruncate(onerel, new_rel_pages);
+
+ /*
+ * We can release the exclusive lock as soon as we have truncated.
+ * Other backends can't safely access the relation until they have
+ * processed the smgr invalidation that smgrtruncate sent out ... but
+ * that should happen as part of standard invalidation processing once
+ * they acquire lock on the relation.
+ */
+ UnlockRelation(onerel, AccessExclusiveLock);
+
+ /*
+ * 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->pages_removed += old_rel_pages - new_rel_pages;
+ vacrelstats->rel_pages = new_rel_pages;
+
+ ereport(elevel,
+ (errmsg("\"%s\": truncated %u to %u pages",
+ RelationGetRelationName(onerel),
+ old_rel_pages, new_rel_pages),
+ errdetail("%s.",
+ pg_rusage_show(&ru0))));
+ old_rel_pages = new_rel_pages;
+ } while (new_rel_pages > vacrelstats->nonempty_pages &&
+ vacrelstats->lock_waiter_detected);
}
/*
count_nondeletable_pages(Relation onerel, LVRelStats *vacrelstats)
{
BlockNumber blkno;
+ instr_time starttime;
+ instr_time currenttime;
+ instr_time elapsed;
+
+ /* Initialize the starttime if we check for conflicting lock requests */
+ INSTR_TIME_SET_CURRENT(starttime);
/* Strange coding of loop control is needed because blkno is unsigned */
blkno = vacrelstats->rel_pages;
maxoff;
bool hastup;
+ /*
+ * Check if another process requests a lock on our relation. We are
+ * holding an AccessExclusiveLock here, so they will be waiting. We
+ * only do this in autovacuum_truncate_lock_check millisecond
+ * intervals, and we only check if that interval has elapsed once
+ * every 32 blocks to keep the number of system calls and actual
+ * shared lock table lookups to a minimum.
+ */
+ if ((blkno % 32) == 0)
+ {
+ INSTR_TIME_SET_CURRENT(currenttime);
+ elapsed = currenttime;
+ INSTR_TIME_SUBTRACT(elapsed, starttime);
+ if ((INSTR_TIME_GET_MICROSEC(elapsed) / 1000)
+ >= AUTOVACUUM_TRUNCATE_LOCK_CHECK_INTERVAL)
+ {
+ if (LockHasWaitersRelation(onerel, AccessExclusiveLock))
+ {
+ ereport(elevel,
+ (errmsg("\"%s\": suspending truncate "
+ "due to conflicting lock request",
+ RelationGetRelationName(onerel))));
+
+ vacrelstats->lock_waiter_detected = true;
+ return blkno;
+ }
+ starttime = currenttime;
+ }
+ }
+
/*
* We don't insert a vacuum delay point here, because we have an
* exclusive lock on the table which we want to hold for as short a
return lockhash;
}
+/*
+ * LockHasWaiters -- look up 'locktag' and check if releasing this
+ * lock would wake up other processes waiting for it.
+ */
+bool
+LockHasWaiters(const LOCKTAG *locktag, LOCKMODE lockmode, bool sessionLock)
+{
+ LOCKMETHODID lockmethodid = locktag->locktag_lockmethodid;
+ LockMethod lockMethodTable;
+ LOCALLOCKTAG localtag;
+ LOCALLOCK *locallock;
+ LOCK *lock;
+ PROCLOCK *proclock;
+ LWLockId partitionLock;
+ bool hasWaiters = false;
+
+ if (lockmethodid <= 0 || lockmethodid >= lengthof(LockMethods))
+ elog(ERROR, "unrecognized lock method: %d", lockmethodid);
+ lockMethodTable = LockMethods[lockmethodid];
+ if (lockmode <= 0 || lockmode > lockMethodTable->numLockModes)
+ elog(ERROR, "unrecognized lock mode: %d", lockmode);
+
+#ifdef LOCK_DEBUG
+ if (LOCK_DEBUG_ENABLED(locktag))
+ elog(LOG, "LockHasWaiters: lock [%u,%u] %s",
+ locktag->locktag_field1, locktag->locktag_field2,
+ lockMethodTable->lockModeNames[lockmode]);
+#endif
+
+ /*
+ * Find the LOCALLOCK entry for this lock and lockmode
+ */
+ MemSet(&localtag, 0, sizeof(localtag)); /* must clear padding */
+ localtag.lock = *locktag;
+ localtag.mode = lockmode;
+
+ locallock = (LOCALLOCK *) hash_search(LockMethodLocalHash,
+ (void *) &localtag,
+ HASH_FIND, NULL);
+
+ /*
+ * let the caller print its own error message, too. Do not ereport(ERROR).
+ */
+ if (!locallock || locallock->nLocks <= 0)
+ {
+ elog(WARNING, "you don't own a lock of type %s",
+ lockMethodTable->lockModeNames[lockmode]);
+ return false;
+ }
+
+ /*
+ * Check the shared lock table.
+ */
+ partitionLock = LockHashPartitionLock(locallock->hashcode);
+
+ LWLockAcquire(partitionLock, LW_SHARED);
+
+ /*
+ * We don't need to re-find the lock or proclock, since we kept their
+ * addresses in the locallock table, and they couldn't have been removed
+ * while we were holding a lock on them.
+ */
+ lock = locallock->lock;
+ LOCK_PRINT("LockHasWaiters: found", lock, lockmode);
+ proclock = locallock->proclock;
+ PROCLOCK_PRINT("LockHasWaiters: found", proclock);
+
+ /*
+ * Double-check that we are actually holding a lock of the type we want to
+ * release.
+ */
+ if (!(proclock->holdMask & LOCKBIT_ON(lockmode)))
+ {
+ PROCLOCK_PRINT("LockHasWaiters: WRONGTYPE", proclock);
+ LWLockRelease(partitionLock);
+ elog(WARNING, "you don't own a lock of type %s",
+ lockMethodTable->lockModeNames[lockmode]);
+ RemoveLocalLock(locallock);
+ return false;
+ }
+
+ /*
+ * Do the checking.
+ */
+ if ((lockMethodTable->conflictTab[lockmode] & lock->waitMask) != 0)
+ hasWaiters = true;
+
+ LWLockRelease(partitionLock);
+
+ return hasWaiters;
+}
+
/*
* LockAcquire -- Check for lock conflicts, sleep if conflict found,
projects / postgresql / commitdiff