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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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51
src/backend/commands/tablecmds.c
View File

@ -8,7 +8,7 @@
*
*
* IDENTIFICATION
* $PostgreSQL: pgsql/src/backend/commands/tablecmds.c,v 1.131 2004/08/31 23:27:05 tgl Exp $
* $PostgreSQL: pgsql/src/backend/commands/tablecmds.c,v 1.132 2004/09/16 16:58:28 tgl Exp $
*
*-------------------------------------------------------------------------
*/
@ -71,14 +71,14 @@ typedef struct OnCommitItem
OnCommitAction oncommit; /* what to do at end of xact */
/*
* If this entry was created during this xact, it should be deleted at
* xact abort. Conversely, if this entry was deleted during this
* xact, it should be removed at xact commit. We leave deleted
* entries in the list until commit so that we can roll back if
* needed.
* If this entry was created during the current transaction,
* creating_subid is the ID of the creating subxact; if created in a prior
* transaction, creating_subid is zero. If deleted during the current
* transaction, deleting_subid is the ID of the deleting subxact; if no
* deletion request is pending, deleting_subid is zero.
*/
TransactionId creating_xid;
TransactionId deleting_xid;
SubTransactionId creating_subid;
SubTransactionId deleting_subid;
} OnCommitItem;
static List *on_commits = NIL;
@ -5821,8 +5821,8 @@ register_on_commit_action(Oid relid, OnCommitAction action)
oc = (OnCommitItem *) palloc(sizeof(OnCommitItem));
oc->relid = relid;
oc->oncommit = action;
oc->creating_xid = GetCurrentTransactionId();
oc->deleting_xid = InvalidTransactionId;
oc->creating_subid = GetCurrentSubTransactionId();
oc->deleting_subid = InvalidSubTransactionId;
on_commits = lcons(oc, on_commits);
@ -5845,7 +5845,7 @@ remove_on_commit_action(Oid relid)
if (oc->relid == relid)
{
oc->deleting_xid = GetCurrentTransactionId();
oc->deleting_subid = GetCurrentSubTransactionId();
break;
}
}
@ -5860,7 +5860,6 @@ remove_on_commit_action(Oid relid)
void
PreCommit_on_commit_actions(void)
{
TransactionId xid = GetCurrentTransactionId();
ListCell *l;
foreach(l, on_commits)
@ -5868,7 +5867,7 @@ PreCommit_on_commit_actions(void)
OnCommitItem *oc = (OnCommitItem *) lfirst(l);
/* Ignore entry if already dropped in this xact */
if (oc->deleting_xid == xid)
if (oc->deleting_subid != InvalidSubTransactionId)
continue;
switch (oc->oncommit)
@ -5895,7 +5894,7 @@ PreCommit_on_commit_actions(void)
* remove_on_commit_action, so the entry should get
* marked as deleted.
*/
Assert(oc->deleting_xid == xid);
Assert(oc->deleting_subid != InvalidSubTransactionId);
break;
}
}
@ -5911,7 +5910,7 @@ PreCommit_on_commit_actions(void)
* during abort, remove those created during this transaction.
*/
void
AtEOXact_on_commit_actions(bool isCommit, TransactionId xid)
AtEOXact_on_commit_actions(bool isCommit)
{
ListCell *cur_item;
ListCell *prev_item;
@ -5923,8 +5922,8 @@ AtEOXact_on_commit_actions(bool isCommit, TransactionId xid)
{
OnCommitItem *oc = (OnCommitItem *) lfirst(cur_item);
if (isCommit ? TransactionIdEquals(oc->deleting_xid, xid) :
TransactionIdEquals(oc->creating_xid, xid))
if (isCommit ? oc->deleting_subid != InvalidSubTransactionId :
oc->creating_subid != InvalidSubTransactionId)
{
/* cur_item must be removed */
on_commits = list_delete_cell(on_commits, cur_item, prev_item);
@ -5937,8 +5936,8 @@ AtEOXact_on_commit_actions(bool isCommit, TransactionId xid)
else
{
/* cur_item must be preserved */
oc->creating_xid = InvalidTransactionId;
oc->deleting_xid = InvalidTransactionId;
oc->creating_subid = InvalidSubTransactionId;
oc->deleting_subid = InvalidSubTransactionId;
prev_item = cur_item;
cur_item = lnext(prev_item);
}
@ -5953,8 +5952,8 @@ AtEOXact_on_commit_actions(bool isCommit, TransactionId xid)
* this subtransaction as being the parent's responsibility.
*/
void
AtEOSubXact_on_commit_actions(bool isCommit, TransactionId childXid,
TransactionId parentXid)
AtEOSubXact_on_commit_actions(bool isCommit, SubTransactionId mySubid,
SubTransactionId parentSubid)
{
ListCell *cur_item;
ListCell *prev_item;
@ -5966,7 +5965,7 @@ AtEOSubXact_on_commit_actions(bool isCommit, TransactionId childXid,
{
OnCommitItem *oc = (OnCommitItem *) lfirst(cur_item);
if (!isCommit && TransactionIdEquals(oc->creating_xid, childXid))
if (!isCommit && oc->creating_subid == mySubid)
{
/* cur_item must be removed */
on_commits = list_delete_cell(on_commits, cur_item, prev_item);
@ -5979,10 +5978,10 @@ AtEOSubXact_on_commit_actions(bool isCommit, TransactionId childXid,
else
{
/* cur_item must be preserved */
if (TransactionIdEquals(oc->creating_xid, childXid))
oc->creating_xid = parentXid;
if (TransactionIdEquals(oc->deleting_xid, childXid))
oc->deleting_xid = isCommit ? parentXid : InvalidTransactionId;
if (oc->creating_subid == mySubid)
oc->creating_subid = parentSubid;
if (oc->deleting_subid == mySubid)
oc->deleting_subid = isCommit ? parentSubid : InvalidSubTransactionId;
prev_item = cur_item;
cur_item = lnext(prev_item);
}