(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
errmsg("cannot truncate temporary tables of other sessions")));
+ /*
+ * Also check for active uses of the relation in the current
+ * transaction, including open scans and pending AFTER trigger events.
+ */
+ CheckTableNotInUse(rel, "TRUNCATE");
+
/* Save it into the list of rels to truncate */
rels = lappend(rels, rel);
}
CommandCounterIncrement();
}
+/*
+ * Disallow ALTER TABLE (and similar commands) when the current backend has
+ * any open reference to the target table besides the one just acquired by
+ * the calling command; this implies there's an open cursor or active plan.
+ * We need this check because our AccessExclusiveLock doesn't protect us
+ * against stomping on our own foot, only other people's feet!
+ *
+ * For ALTER TABLE, the only case known to cause serious trouble is ALTER
+ * COLUMN TYPE, and some changes are obviously pretty benign, so this could
+ * possibly be relaxed to only error out for certain types of alterations.
+ * But the use-case for allowing any of these things is not obvious, so we
+ * won't work hard at it for now.
+ *
+ * We also reject these commands if there are any pending AFTER trigger events
+ * for the rel. This is certainly necessary for the rewriting variants of
+ * ALTER TABLE, because they don't preserve tuple TIDs and so the pending
+ * events would try to fetch the wrong tuples. It might be overly cautious
+ * in other cases, but again it seems better to err on the side of paranoia.
+ *
+ * REINDEX calls this with "rel" referencing the index to be rebuilt; here
+ * we are worried about active indexscans on the index. The trigger-event
+ * check can be skipped, since we are doing no damage to the parent table.
+ *
+ * The statement name (eg, "ALTER TABLE") is passed for use in error messages.
+ */
+void
+CheckTableNotInUse(Relation rel, const char *stmt)
+{
+ int expected_refcnt;
+
+ expected_refcnt = rel->rd_isnailed ? 2 : 1;
+ if (rel->rd_refcnt != expected_refcnt)
+ ereport(ERROR,
+ (errcode(ERRCODE_OBJECT_IN_USE),
+ /* translator: first %s is a SQL command, eg ALTER TABLE */
+ errmsg("cannot %s \"%s\" because "
+ "it is being used by active queries in this session",
+ stmt, RelationGetRelationName(rel))));
+
+ if (rel->rd_rel->relkind != RELKIND_INDEX &&
+ AfterTriggerPendingOnRel(RelationGetRelid(rel)))
+ ereport(ERROR,
+ (errcode(ERRCODE_OBJECT_IN_USE),
+ /* translator: first %s is a SQL command, eg ALTER TABLE */
+ errmsg("cannot %s \"%s\" because "
+ "it has pending trigger events",
+ stmt, RelationGetRelationName(rel))));
+}
+
/*
* AlterTable
* Execute ALTER TABLE, which can be a list of subcommands
AlterTable(AlterTableStmt *stmt)
{
Relation rel = relation_openrv(stmt->relation, AccessExclusiveLock);
- int expected_refcnt;
- /*
- * Disallow ALTER TABLE when the current backend has any open reference
- * to it besides the one we just got (such as an open cursor or active
- * plan); our AccessExclusiveLock doesn't protect us against stomping on
- * our own foot, only other people's feet!
- *
- * Note: the only case known to cause serious trouble is ALTER COLUMN TYPE,
- * and some changes are obviously pretty benign, so this could possibly
- * be relaxed to only error out for certain types of alterations. But
- * the use-case for allowing any of these things is not obvious, so we
- * won't work hard at it for now.
- */
- expected_refcnt = rel->rd_isnailed ? 2 : 1;
- if (rel->rd_refcnt != expected_refcnt)
- ereport(ERROR,
- (errcode(ERRCODE_OBJECT_IN_USE),
- errmsg("relation \"%s\" is being used by active queries in this session",
- RelationGetRelationName(rel))));
+ CheckTableNotInUse(rel, "ALTER TABLE");
ATController(rel, stmt->cmds, interpretInhOption(stmt->relation->inhOpt));
}
* We do not reject if the relation is already open, because it's quite
* likely that one or more layers of caller have it open. That means it
* is unsafe to use this entry point for alterations that could break
- * existing query plans.
+ * existing query plans. On the assumption it's not used for such, we
+ * don't have to reject pending AFTER triggers, either.
*/
void
AlterTableInternal(Oid relid, List *cmds, bool recurse)
if (childrelid == relid)
continue;
childrel = relation_open(childrelid, AccessExclusiveLock);
- /* check for child relation in use in this session */
- if (childrel->rd_refcnt != 1)
- ereport(ERROR,
- (errcode(ERRCODE_OBJECT_IN_USE),
- errmsg("relation \"%s\" is being used by active queries in this session",
- RelationGetRelationName(childrel))));
+ CheckTableNotInUse(childrel, "ALTER TABLE");
ATPrepCmd(wqueue, childrel, cmd, false, true);
relation_close(childrel, NoLock);
}
Relation childrel;
childrel = relation_open(childrelid, AccessExclusiveLock);
- /* check for child relation in use in this session */
- if (childrel->rd_refcnt != 1)
- ereport(ERROR,
- (errcode(ERRCODE_OBJECT_IN_USE),
- errmsg("relation \"%s\" is being used by active queries in this session",
- RelationGetRelationName(childrel))));
+ CheckTableNotInUse(childrel, "ALTER TABLE");
ATPrepCmd(wqueue, childrel, cmd, true, true);
relation_close(childrel, NoLock);
}
Form_pg_attribute childatt;
childrel = heap_open(childrelid, AccessExclusiveLock);
- /* check for child relation in use in this session */
- if (childrel->rd_refcnt != 1)
- ereport(ERROR,
- (errcode(ERRCODE_OBJECT_IN_USE),
- errmsg("relation \"%s\" is being used by active queries in this session",
- RelationGetRelationName(childrel))));
+ CheckTableNotInUse(childrel, "ALTER TABLE");
tuple = SearchSysCacheCopyAttName(childrelid, colName);
if (!HeapTupleIsValid(tuple)) /* shouldn't happen */
}
}
+/* ----------
+ * AfterTriggerPendingOnRel()
+ * Test to see if there are any pending after-trigger events for rel.
+ *
+ * This is used by TRUNCATE, CLUSTER, ALTER TABLE, etc to detect whether
+ * it is unsafe to perform major surgery on a relation. Note that only
+ * local pending events are examined. We assume that having exclusive lock
+ * on a rel guarantees there are no unserviced events in other backends ---
+ * but having a lock does not prevent there being such events in our own.
+ *
+ * In some scenarios it'd be reasonable to remove pending events (more
+ * specifically, mark them DONE by the current subxact) but without a lot
+ * of knowledge of the trigger semantics we can't do this in general.
+ * ----------
+ */
+bool
+AfterTriggerPendingOnRel(Oid relid)
+{
+ AfterTriggerEvent event;
+ int depth;
+
+ /* No-op if we aren't in a transaction. (Shouldn't happen?) */
+ if (afterTriggers == NULL)
+ return false;
+
+ /* Scan queued events */
+ for (event = afterTriggers->events.head;
+ event != NULL;
+ event = event->ate_next)
+ {
+ /*
+ * We can ignore completed events. (Even if a DONE flag is rolled
+ * back by subxact abort, it's OK because the effects of the TRUNCATE
+ * or whatever must get rolled back too.)
+ */
+ if (event->ate_event & AFTER_TRIGGER_DONE)
+ continue;
+
+ if (event->ate_relid == relid)
+ return true;
+ }
+
+ /*
+ * Also scan events queued by incomplete queries. This could only matter
+ * if TRUNCATE/etc is executed by a function or trigger within an updating
+ * query on the same relation, which is pretty perverse, but let's check.
+ */
+ for (depth = 0; depth <= afterTriggers->query_depth; depth++)
+ {
+ for (event = afterTriggers->query_stack[depth].head;
+ event != NULL;
+ event = event->ate_next)
+ {
+ if (event->ate_event & AFTER_TRIGGER_DONE)
+ continue;
+
+ if (event->ate_relid == relid)
+ return true;
+ }
+ }
+
+ return false;
+}
+
/* ----------
* AfterTriggerSaveEvent()
projects / users / bernd / postgres.git / commitdiff