*
*
* IDENTIFICATION
- * $PostgreSQL: pgsql/src/backend/commands/vacuum.c,v 1.276 2004/05/21 16:08:46 tgl Exp $
+ * $PostgreSQL: pgsql/src/backend/commands/vacuum.c,v 1.277 2004/05/22 23:14:38 tgl Exp $
*
*-------------------------------------------------------------------------
*/
MemoryContext anl_context = NULL;
TransactionId initialOldestXmin = InvalidTransactionId;
TransactionId initialFreezeLimit = InvalidTransactionId;
- bool all_rels;
+ bool all_rels,
+ in_outer_xact,
+ use_own_xacts;
List *relations,
*cur;
* Furthermore, the forced commit that occurs before truncating the
* relation's file would have the effect of committing the rest of the
* user's transaction too, which would certainly not be the desired
- * behavior.
+ * behavior. (This only applies to VACUUM FULL, though. We could
+ * in theory run lazy VACUUM inside a transaction block, but we choose
+ * to disallow that case because we'd rather commit as soon as possible
+ * after finishing the vacuum. This is mainly so that we can let go the
+ * AccessExclusiveLock that we may be holding.)
+ *
+ * ANALYZE (without VACUUM) can run either way.
*/
if (vacstmt->vacuum)
+ {
PreventTransactionChain((void *) vacstmt, stmttype);
+ in_outer_xact = false;
+ }
+ else
+ {
+ in_outer_xact = IsInTransactionChain((void *) vacstmt);
+ }
/* Turn vacuum cost accounting on or off */
VacuumCostActive = (VacuumCostNaptime > 0);
ALLOCSET_DEFAULT_INITSIZE,
ALLOCSET_DEFAULT_MAXSIZE);
- /*
- * If we are running only ANALYZE, we don't need per-table
- * transactions, but we still need a memory context with table
- * lifetime.
- */
- if (vacstmt->analyze && !vacstmt->vacuum)
- anl_context = AllocSetContextCreate(PortalContext,
- "Analyze",
- ALLOCSET_DEFAULT_MINSIZE,
- ALLOCSET_DEFAULT_INITSIZE,
- ALLOCSET_DEFAULT_MAXSIZE);
-
/* Assume we are processing everything unless one table is mentioned */
all_rels = (vacstmt->relation == NULL);
/* Build list of relations to process (note this lives in vac_context) */
relations = get_rel_oids(vacstmt->relation, stmttype);
+ if (vacstmt->vacuum && all_rels)
+ {
+ /*
+ * It's a database-wide VACUUM.
+ *
+ * Compute the initially applicable OldestXmin and FreezeLimit
+ * XIDs, so that we can record these values at the end of the
+ * VACUUM. Note that individual tables may well be processed
+ * with newer values, but we can guarantee that no
+ * (non-shared) relations are processed with older ones.
+ *
+ * It is okay to record non-shared values in pg_database, even
+ * though we may vacuum shared relations with older cutoffs,
+ * because only the minimum of the values present in
+ * pg_database matters. We can be sure that shared relations
+ * have at some time been vacuumed with cutoffs no worse than
+ * the global minimum; for, if there is a backend in some
+ * other DB with xmin = OLDXMIN that's determining the cutoff
+ * with which we vacuum shared relations, it is not possible
+ * for that database to have a cutoff newer than OLDXMIN
+ * recorded in pg_database.
+ */
+ vacuum_set_xid_limits(vacstmt, false,
+ &initialOldestXmin,
+ &initialFreezeLimit);
+ }
+
/*
- * Formerly, there was code here to prevent more than one VACUUM from
- * executing concurrently in the same database. However, there's no
- * good reason to prevent that, and manually removing lockfiles after
- * a vacuum crash was a pain for dbadmins. So, forget about
- * lockfiles, and just rely on the locks we grab on each target table
- * to ensure that there aren't two VACUUMs running on the same table
- * at the same time.
+ * Decide whether we need to start/commit our own transactions.
+ *
+ * For VACUUM (with or without ANALYZE): always do so, so that we
+ * can release locks as soon as possible. (We could possibly use the
+ * outer transaction for a one-table VACUUM, but handling TOAST tables
+ * would be problematic.)
+ *
+ * For ANALYZE (no VACUUM): if inside a transaction block, we cannot
+ * start/commit our own transactions. Also, there's no need to do so
+ * if only processing one relation. For multiple relations when not
+ * within a transaction block, use own transactions so we can release
+ * locks sooner.
*/
+ if (vacstmt->vacuum)
+ {
+ use_own_xacts = true;
+ }
+ else
+ {
+ Assert(vacstmt->analyze);
+ if (in_outer_xact)
+ use_own_xacts = false;
+ else if (length(relations) > 1)
+ use_own_xacts = true;
+ else
+ use_own_xacts = false;
+ }
+
+ /*
+ * If we are running ANALYZE without per-table transactions, we'll
+ * need a memory context with table lifetime.
+ */
+ if (!use_own_xacts)
+ anl_context = AllocSetContextCreate(PortalContext,
+ "Analyze",
+ ALLOCSET_DEFAULT_MINSIZE,
+ ALLOCSET_DEFAULT_INITSIZE,
+ ALLOCSET_DEFAULT_MAXSIZE);
/*
- * The strangeness with committing and starting transactions here is
- * due to wanting to run each table's VACUUM as a separate
- * transaction, so that we don't hold locks unnecessarily long. Also,
- * if we are doing VACUUM ANALYZE, the ANALYZE part runs as a separate
- * transaction from the VACUUM to further reduce locking.
- *
* vacuum_rel expects to be entered with no transaction active; it will
* start and commit its own transaction. But we are called by an SQL
* command, and so we are executing inside a transaction already. We
* commit the transaction started in PostgresMain() here, and start
* another one before exiting to match the commit waiting for us back
* in PostgresMain().
- *
- * In the case of an ANALYZE statement (no vacuum, just analyze) it's
- * okay to run the whole thing in the outer transaction, and so we
- * skip transaction start/stop operations.
*/
- if (vacstmt->vacuum)
+ if (use_own_xacts)
{
- if (all_rels)
- {
- /*
- * It's a database-wide VACUUM.
- *
- * Compute the initially applicable OldestXmin and FreezeLimit
- * XIDs, so that we can record these values at the end of the
- * VACUUM. Note that individual tables may well be processed
- * with newer values, but we can guarantee that no
- * (non-shared) relations are processed with older ones.
- *
- * It is okay to record non-shared values in pg_database, even
- * though we may vacuum shared relations with older cutoffs,
- * because only the minimum of the values present in
- * pg_database matters. We can be sure that shared relations
- * have at some time been vacuumed with cutoffs no worse than
- * the global minimum; for, if there is a backend in some
- * other DB with xmin = OLDXMIN that's determining the cutoff
- * with which we vacuum shared relations, it is not possible
- * for that database to have a cutoff newer than OLDXMIN
- * recorded in pg_database.
- */
- vacuum_set_xid_limits(vacstmt, false,
- &initialOldestXmin,
- &initialFreezeLimit);
- }
-
/* matches the StartTransaction in PostgresMain() */
CommitTransactionCommand();
}
MemoryContext old_context = NULL;
/*
- * If we vacuumed, use new transaction for analyze. Otherwise,
+ * If using separate xacts, start one for analyze. Otherwise,
* we can use the outer transaction, but we still need to call
* analyze_rel in a memory context that will be cleaned up on
* return (else we leak memory while processing multiple
* tables).
*/
- if (vacstmt->vacuum)
+ if (use_own_xacts)
{
StartTransactionCommand();
SetQuerySnapshot(); /* might be needed for functions
StrategyHintVacuum(false);
- if (vacstmt->vacuum)
+ if (use_own_xacts)
CommitTransactionCommand();
else
{
/*
* Finish up processing.
*/
- if (vacstmt->vacuum)
+ if (use_own_xacts)
{
/* here, we are not in a transaction */
* PostgresMain().
*/
StartTransactionCommand();
+ }
+ if (vacstmt->vacuum)
+ {
/*
* If it was a database-wide VACUUM, print FSM usage statistics
* (we don't make you be superuser to see these).
projects / postgresql / commitdiff