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-rw-r--r--src/backend/commands/portalcmds.c6
-rw-r--r--src/backend/tcop/pquery.c70
-rw-r--r--src/backend/utils/mmgr/portalmem.c16
-rw-r--r--src/include/utils/portal.h10
4 files changed, 80 insertions, 22 deletions
diff --git a/src/backend/commands/portalcmds.c b/src/backend/commands/portalcmds.c
index 50a54e74633..e52830f7ec2 100644
--- a/src/backend/commands/portalcmds.c
+++ b/src/backend/commands/portalcmds.c
@@ -317,10 +317,11 @@ PersistHoldablePortal(Portal portal)
Assert(queryDesc != NULL);
/*
- * Caller must have created the tuplestore already.
+ * Caller must have created the tuplestore already ... but not a snapshot.
*/
Assert(portal->holdContext != NULL);
Assert(portal->holdStore != NULL);
+ Assert(portal->holdSnapshot == NULL);
/*
* Before closing down the executor, we must copy the tupdesc into
@@ -362,7 +363,8 @@ PersistHoldablePortal(Portal portal)
/*
* Change the destination to output to the tuplestore. Note we tell
- * the tuplestore receiver to detoast all data passed through it.
+ * the tuplestore receiver to detoast all data passed through it; this
+ * makes it safe to not keep a snapshot associated with the data.
*/
queryDesc->dest = CreateDestReceiver(DestTuplestore);
SetTuplestoreDestReceiverParams(queryDesc->dest,
diff --git a/src/backend/tcop/pquery.c b/src/backend/tcop/pquery.c
index 3f6cb12b4e5..92d07fcb5db 100644
--- a/src/backend/tcop/pquery.c
+++ b/src/backend/tcop/pquery.c
@@ -43,9 +43,11 @@ static uint64 RunFromStore(Portal portal, ScanDirection direction, uint64 count,
DestReceiver *dest);
static uint64 PortalRunSelect(Portal portal, bool forward, long count,
DestReceiver *dest);
-static void PortalRunUtility(Portal portal, Node *utilityStmt, bool isTopLevel,
+static void PortalRunUtility(Portal portal, Node *utilityStmt,
+ bool isTopLevel, bool setHoldSnapshot,
DestReceiver *dest, char *completionTag);
-static void PortalRunMulti(Portal portal, bool isTopLevel,
+static void PortalRunMulti(Portal portal,
+ bool isTopLevel, bool setHoldSnapshot,
DestReceiver *dest, DestReceiver *altdest,
char *completionTag);
static uint64 DoPortalRunFetch(Portal portal,
@@ -810,7 +812,7 @@ PortalRun(Portal portal, long count, bool isTopLevel,
break;
case PORTAL_MULTI_QUERY:
- PortalRunMulti(portal, isTopLevel,
+ PortalRunMulti(portal, isTopLevel, false,
dest, altdest, completionTag);
/* Prevent portal's commands from being re-executed */
@@ -1039,15 +1041,16 @@ FillPortalStore(Portal portal, bool isTopLevel)
/*
* Run the portal to completion just as for the default
* MULTI_QUERY case, but send the primary query's output to the
- * tuplestore. Auxiliary query outputs are discarded.
+ * tuplestore. Auxiliary query outputs are discarded. Set the
+ * portal's holdSnapshot to the snapshot used (or a copy of it).
*/
- PortalRunMulti(portal, isTopLevel,
+ PortalRunMulti(portal, isTopLevel, true,
treceiver, None_Receiver, completionTag);
break;
case PORTAL_UTIL_SELECT:
PortalRunUtility(portal, (Node *) linitial(portal->stmts),
- isTopLevel, treceiver, completionTag);
+ isTopLevel, true, treceiver, completionTag);
break;
default:
@@ -1142,10 +1145,11 @@ RunFromStore(Portal portal, ScanDirection direction, uint64 count,
* Execute a utility statement inside a portal.
*/
static void
-PortalRunUtility(Portal portal, Node *utilityStmt, bool isTopLevel,
+PortalRunUtility(Portal portal, Node *utilityStmt,
+ bool isTopLevel, bool setHoldSnapshot,
DestReceiver *dest, char *completionTag)
{
- bool active_snapshot_set;
+ Snapshot snapshot;
elog(DEBUG3, "ProcessUtility");
@@ -1172,11 +1176,19 @@ PortalRunUtility(Portal portal, Node *utilityStmt, bool isTopLevel,
IsA(utilityStmt, UnlistenStmt) ||
IsA(utilityStmt, CheckPointStmt)))
{
- PushActiveSnapshot(GetTransactionSnapshot());
- active_snapshot_set = true;
+ snapshot = GetTransactionSnapshot();
+ /* If told to, register the snapshot we're using and save in portal */
+ if (setHoldSnapshot)
+ {
+ snapshot = RegisterSnapshot(snapshot);
+ portal->holdSnapshot = snapshot;
+ }
+ PushActiveSnapshot(snapshot);
+ /* PushActiveSnapshot might have copied the snapshot */
+ snapshot = GetActiveSnapshot();
}
else
- active_snapshot_set = false;
+ snapshot = NULL;
ProcessUtility(utilityStmt,
portal->sourceText,
@@ -1190,12 +1202,11 @@ PortalRunUtility(Portal portal, Node *utilityStmt, bool isTopLevel,
/*
* Some utility commands may pop the ActiveSnapshot stack from under us,
- * so we only pop the stack if we actually see a snapshot set. Note that
- * the set of utility commands that do this must be the same set
- * disallowed to run inside a transaction; otherwise, we could be popping
- * a snapshot that belongs to some other operation.
+ * so be careful to only pop the stack if our snapshot is still at the
+ * top.
*/
- if (active_snapshot_set && ActiveSnapshotSet())
+ if (snapshot != NULL && ActiveSnapshotSet() &&
+ snapshot == GetActiveSnapshot())
PopActiveSnapshot();
}
@@ -1205,7 +1216,8 @@ PortalRunUtility(Portal portal, Node *utilityStmt, bool isTopLevel,
* or non-SELECT-like queries)
*/
static void
-PortalRunMulti(Portal portal, bool isTopLevel,
+PortalRunMulti(Portal portal,
+ bool isTopLevel, bool setHoldSnapshot,
DestReceiver *dest, DestReceiver *altdest,
char *completionTag)
{
@@ -1261,7 +1273,25 @@ PortalRunMulti(Portal portal, bool isTopLevel,
*/
if (!active_snapshot_set)
{
- PushActiveSnapshot(GetTransactionSnapshot());
+ Snapshot snapshot = GetTransactionSnapshot();
+
+ /* If told to, register the snapshot and save in portal */
+ if (setHoldSnapshot)
+ {
+ snapshot = RegisterSnapshot(snapshot);
+ portal->holdSnapshot = snapshot;
+ }
+
+ /*
+ * We can't have the holdSnapshot also be the active one,
+ * because UpdateActiveSnapshotCommandId would complain. So
+ * force an extra snapshot copy. Plain PushActiveSnapshot
+ * would have copied the transaction snapshot anyway, so this
+ * only adds a copy step when setHoldSnapshot is true. (It's
+ * okay for the command ID of the active snapshot to diverge
+ * from what holdSnapshot has.)
+ */
+ PushCopiedSnapshot(snapshot);
active_snapshot_set = true;
}
else
@@ -1309,14 +1339,14 @@ PortalRunMulti(Portal portal, bool isTopLevel,
{
Assert(!active_snapshot_set);
/* statement can set tag string */
- PortalRunUtility(portal, stmt, isTopLevel,
+ PortalRunUtility(portal, stmt, isTopLevel, false,
dest, completionTag);
}
else
{
Assert(IsA(stmt, NotifyStmt));
/* stmt added by rewrite cannot set tag */
- PortalRunUtility(portal, stmt, isTopLevel,
+ PortalRunUtility(portal, stmt, isTopLevel, false,
altdest, NULL);
}
}
diff --git a/src/backend/utils/mmgr/portalmem.c b/src/backend/utils/mmgr/portalmem.c
index 053b613cb23..425cae12ea1 100644
--- a/src/backend/utils/mmgr/portalmem.c
+++ b/src/backend/utils/mmgr/portalmem.c
@@ -24,6 +24,7 @@
#include "miscadmin.h"
#include "utils/builtins.h"
#include "utils/memutils.h"
+#include "utils/snapmgr.h"
#include "utils/timestamp.h"
/*
@@ -351,6 +352,7 @@ PortalCreateHoldStore(Portal portal)
Assert(portal->holdContext == NULL);
Assert(portal->holdStore == NULL);
+ Assert(portal->holdSnapshot == NULL);
/*
* Create the memory context that is used for storage of the tuple set.
@@ -527,6 +529,20 @@ PortalDrop(Portal portal, bool isTopCommit)
PortalReleaseCachedPlan(portal);
/*
+ * If portal has a snapshot protecting its data, release that. This needs
+ * a little care since the registration will be attached to the portal's
+ * resowner; if the portal failed, we will already have released the
+ * resowner (and the snapshot) during transaction abort.
+ */
+ if (portal->holdSnapshot)
+ {
+ if (portal->resowner)
+ UnregisterSnapshotFromOwner(portal->holdSnapshot,
+ portal->resowner);
+ portal->holdSnapshot = NULL;
+ }
+
+ /*
* Release any resources still attached to the portal. There are several
* cases being covered here:
*
diff --git a/src/include/utils/portal.h b/src/include/utils/portal.h
index 7250c9c1bb3..c1d93a96bb4 100644
--- a/src/include/utils/portal.h
+++ b/src/include/utils/portal.h
@@ -163,6 +163,16 @@ typedef struct PortalData
MemoryContext holdContext; /* memory containing holdStore */
/*
+ * Snapshot under which tuples in the holdStore were read. We must keep a
+ * reference to this snapshot if there is any possibility that the tuples
+ * contain TOAST references, because releasing the snapshot could allow
+ * recently-dead rows to be vacuumed away, along with any toast data
+ * belonging to them. In the case of a held cursor, we avoid needing to
+ * keep such a snapshot by forcibly detoasting the data.
+ */
+ Snapshot holdSnapshot; /* registered snapshot, or NULL if none */
+
+ /*
* atStart, atEnd and portalPos indicate the current cursor position.
* portalPos is zero before the first row, N after fetching N'th row of
* query. After we run off the end, portalPos = # of rows in query, and
generated by cgit v1.2.3 (git 2.25.1) at 2025-05-29 08:58:15 +0000