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Restructure subtransaction handling to reduce resource consumption,

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as per recent discussions.  Invent SubTransactionIds that are managed like
CommandIds (ie, counter is reset at start of each top transaction), and
use these instead of TransactionIds to keep track of subtransaction status
in those modules that need it.  This means that a subtransaction does not
need an XID unless it actually inserts/modifies rows in the database.
Accordingly, don't assign it an XID nor take a lock on the XID until it
tries to do that.  This saves a lot of overhead for subtransactions that
are only used for error recovery (eg plpgsql exceptions).  Also, arrange
to release a subtransaction's XID lock as soon as the subtransaction
exits, in both the commit and abort cases.  This avoids holding many
unique locks after a long series of subtransactions.  The price is some
additional overhead in XactLockTableWait, but that seems acceptable.
Finally, restructure the state machine in xact.c to have a more orthogonal
set of states for subtransactions.
This commit is contained in:
Tom Lane
2004-09-16 16:58:44 +00:00
parent 42c0d1f3cd
commit 8f9f198603
34 changed files with 1220 additions and 945 deletions
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30
src/backend/catalog/namespace.c
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@@ -13,7 +13,7 @@
* Portions Copyright (c) 1994, Regents of the University of California
*
* IDENTIFICATION
* $PostgreSQL: pgsql/src/backend/catalog/namespace.c,v 1.70 2004/08/29 05:06:41 momjian Exp $
* $PostgreSQL: pgsql/src/backend/catalog/namespace.c,v 1.71 2004/09/16 16:58:27 tgl Exp $
*
*-------------------------------------------------------------------------
*/
@@ -108,16 +108,16 @@ static bool namespaceSearchPathValid = true;
* in a particular backend session (this happens when a CREATE TEMP TABLE
* command is first executed). Thereafter it's the OID of the temp namespace.
*
* myTempNamespaceXID shows whether we've created the TEMP namespace in the
* current transaction. The TransactionId propagates up the transaction tree,
* myTempNamespaceSubID shows whether we've created the TEMP namespace in the
* current subtransaction. The flag propagates up the subtransaction tree,
* so the main transaction will correctly recognize the flag if all
* intermediate subtransactions commit. When it is InvalidTransactionId,
* intermediate subtransactions commit. When it is InvalidSubTransactionId,
* we either haven't made the TEMP namespace yet, or have successfully
* committed its creation, depending on whether myTempNamespace is valid.
*/
static Oid myTempNamespace = InvalidOid;
static TransactionId myTempNamespaceXID = InvalidTransactionId;
static SubTransactionId myTempNamespaceSubID = InvalidSubTransactionId;
/*
* "Special" namespace for CREATE SCHEMA. If set, it's the first search
@@ -1696,8 +1696,8 @@ InitTempTableNamespace(void)
myTempNamespace = namespaceId;
/* It should not be done already. */
AssertState(myTempNamespaceXID == InvalidTransactionId);
myTempNamespaceXID = GetCurrentTransactionId();
AssertState(myTempNamespaceSubID == InvalidSubTransactionId);
myTempNamespaceSubID = GetCurrentSubTransactionId();
namespaceSearchPathValid = false; /* need to rebuild list */
}
@@ -1716,7 +1716,7 @@ AtEOXact_Namespace(bool isCommit)
* temp tables at backend shutdown. (We only want to register the
* callback once per session, so this is a good place to do it.)
*/
if (myTempNamespaceXID == GetCurrentTransactionId())
if (myTempNamespaceSubID != InvalidSubTransactionId)
{
if (isCommit)
on_shmem_exit(RemoveTempRelationsCallback, 0);
@@ -1725,7 +1725,7 @@ AtEOXact_Namespace(bool isCommit)
myTempNamespace = InvalidOid;
namespaceSearchPathValid = false; /* need to rebuild list */
}
myTempNamespaceXID = InvalidTransactionId;
myTempNamespaceSubID = InvalidSubTransactionId;
}
/*
@@ -1742,21 +1742,21 @@ AtEOXact_Namespace(bool isCommit)
* AtEOSubXact_Namespace
*
* At subtransaction commit, propagate the temp-namespace-creation
* flag to the parent transaction.
* flag to the parent subtransaction.
*
* At subtransaction abort, forget the flag if we set it up.
*/
void
AtEOSubXact_Namespace(bool isCommit, TransactionId myXid,
TransactionId parentXid)
AtEOSubXact_Namespace(bool isCommit, SubTransactionId mySubid,
SubTransactionId parentSubid)
{
if (myTempNamespaceXID == myXid)
if (myTempNamespaceSubID == mySubid)
{
if (isCommit)
myTempNamespaceXID = parentXid;
myTempNamespaceSubID = parentSubid;
else
{
myTempNamespaceXID = InvalidTransactionId;
myTempNamespaceSubID = InvalidSubTransactionId;
/* TEMP namespace creation failed, so reset state */
myTempNamespace = InvalidOid;
namespaceSearchPathValid = false; /* need to rebuild list */