diff options
Diffstat (limited to 'src/backend/tcop/pquery.c')
-rw-r--r-- | src/backend/tcop/pquery.c | 135 |
1 files changed, 104 insertions, 31 deletions
diff --git a/src/backend/tcop/pquery.c b/src/backend/tcop/pquery.c index f5b780e32bb..c9f63923543 100644 --- a/src/backend/tcop/pquery.c +++ b/src/backend/tcop/pquery.c @@ -490,6 +490,13 @@ PortalStart(Portal portal, ParamListInfo params, PushActiveSnapshot(GetTransactionSnapshot()); /* + * We could remember the snapshot in portal->portalSnapshot, + * but presently there seems no need to, as this code path + * cannot be used for non-atomic execution. Hence there can't + * be any commit/abort that might destroy the snapshot. + */ + + /* * Create QueryDesc in portal's context; for the moment, set * the destination to DestNone. */ @@ -1132,45 +1139,26 @@ PortalRunUtility(Portal portal, PlannedStmt *pstmt, bool isTopLevel, bool setHoldSnapshot, DestReceiver *dest, char *completionTag) { - Node *utilityStmt = pstmt->utilityStmt; - Snapshot snapshot; - /* - * Set snapshot if utility stmt needs one. Most reliable way to do this - * seems to be to enumerate those that do not need one; this is a short - * list. Transaction control, LOCK, and SET must *not* set a snapshot - * since they need to be executable at the start of a transaction-snapshot - * mode transaction without freezing a snapshot. By extension we allow - * SHOW not to set a snapshot. The other stmts listed are just efficiency - * hacks. Beware of listing anything that can modify the database --- if, - * say, it has to update an index with expressions that invoke - * user-defined functions, then it had better have a snapshot. + * Set snapshot if utility stmt needs one. */ - if (!(IsA(utilityStmt, TransactionStmt) || - IsA(utilityStmt, LockStmt) || - IsA(utilityStmt, VariableSetStmt) || - IsA(utilityStmt, VariableShowStmt) || - IsA(utilityStmt, ConstraintsSetStmt) || - /* efficiency hacks from here down */ - IsA(utilityStmt, FetchStmt) || - IsA(utilityStmt, ListenStmt) || - IsA(utilityStmt, NotifyStmt) || - IsA(utilityStmt, UnlistenStmt) || - IsA(utilityStmt, CheckPointStmt))) + if (PlannedStmtRequiresSnapshot(pstmt)) { - snapshot = GetTransactionSnapshot(); + Snapshot snapshot = GetTransactionSnapshot(); + /* If told to, register the snapshot we're using and save in portal */ if (setHoldSnapshot) { snapshot = RegisterSnapshot(snapshot); portal->holdSnapshot = snapshot; } + /* In any case, make the snapshot active and remember it in portal */ PushActiveSnapshot(snapshot); /* PushActiveSnapshot might have copied the snapshot */ - snapshot = GetActiveSnapshot(); + portal->portalSnapshot = GetActiveSnapshot(); } else - snapshot = NULL; + portal->portalSnapshot = NULL; ProcessUtility(pstmt, portal->sourceText, @@ -1184,13 +1172,17 @@ PortalRunUtility(Portal portal, PlannedStmt *pstmt, MemoryContextSwitchTo(portal->portalContext); /* - * Some utility commands may pop the ActiveSnapshot stack from under us, - * so be careful to only pop the stack if our snapshot is still at the - * top. + * Some utility commands (e.g., VACUUM) pop the ActiveSnapshot stack from + * under us, so don't complain if it's now empty. Otherwise, our snapshot + * should be the top one; pop it. Note that this could be a different + * snapshot from the one we made above; see EnsurePortalSnapshotExists. */ - if (snapshot != NULL && ActiveSnapshotSet() && - snapshot == GetActiveSnapshot()) + if (portal->portalSnapshot != NULL && ActiveSnapshotSet()) + { + Assert(portal->portalSnapshot == GetActiveSnapshot()); PopActiveSnapshot(); + } + portal->portalSnapshot = NULL; } /* @@ -1272,6 +1264,12 @@ PortalRunMulti(Portal portal, * from what holdSnapshot has.) */ PushCopiedSnapshot(snapshot); + + /* + * As for PORTAL_ONE_SELECT portals, it does not seem + * necessary to maintain portal->portalSnapshot here. + */ + active_snapshot_set = true; } else @@ -1714,3 +1712,78 @@ DoPortalRewind(Portal portal) portal->atEnd = false; portal->portalPos = 0; } + +/* + * PlannedStmtRequiresSnapshot - what it says on the tin + */ +bool +PlannedStmtRequiresSnapshot(PlannedStmt *pstmt) +{ + Node *utilityStmt = pstmt->utilityStmt; + + /* If it's not a utility statement, it definitely needs a snapshot */ + if (utilityStmt == NULL) + return true; + + /* + * Most utility statements need a snapshot, and the default presumption + * about new ones should be that they do too. Hence, enumerate those that + * do not need one. + * + * Transaction control, LOCK, and SET must *not* set a snapshot, since + * they need to be executable at the start of a transaction-snapshot-mode + * transaction without freezing a snapshot. By extension we allow SHOW + * not to set a snapshot. The other stmts listed are just efficiency + * hacks. Beware of listing anything that can modify the database --- if, + * say, it has to update an index with expressions that invoke + * user-defined functions, then it had better have a snapshot. + */ + if (IsA(utilityStmt, TransactionStmt) || + IsA(utilityStmt, LockStmt) || + IsA(utilityStmt, VariableSetStmt) || + IsA(utilityStmt, VariableShowStmt) || + IsA(utilityStmt, ConstraintsSetStmt) || + /* efficiency hacks from here down */ + IsA(utilityStmt, FetchStmt) || + IsA(utilityStmt, ListenStmt) || + IsA(utilityStmt, NotifyStmt) || + IsA(utilityStmt, UnlistenStmt) || + IsA(utilityStmt, CheckPointStmt)) + return false; + + return true; +} + +/* + * EnsurePortalSnapshotExists - recreate Portal-level snapshot, if needed + * + * Generally, we will have an active snapshot whenever we are executing + * inside a Portal, unless the Portal's query is one of the utility + * statements exempted from that rule (see PlannedStmtRequiresSnapshot). + * However, procedures and DO blocks can commit or abort the transaction, + * and thereby destroy all snapshots. This function can be called to + * re-establish the Portal-level snapshot when none exists. + */ +void +EnsurePortalSnapshotExists(void) +{ + Portal portal; + + /* + * Nothing to do if a snapshot is set. (We take it on faith that the + * outermost active snapshot belongs to some Portal; or if there is no + * Portal, it's somebody else's responsibility to manage things.) + */ + if (ActiveSnapshotSet()) + return; + + /* Otherwise, we'd better have an active Portal */ + portal = ActivePortal; + Assert(portal != NULL); + Assert(portal->portalSnapshot == NULL); + + /* Create a new snapshot and make it active */ + PushActiveSnapshot(GetTransactionSnapshot()); + /* PushActiveSnapshot might have copied the snapshot */ + portal->portalSnapshot = GetActiveSnapshot(); +} |