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Fix TransactionIdIsCurrentTransactionId() to use binary search instead of

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linear search when checking child-transaction XIDs.  This makes for an
important speedup in transactions that have large numbers of children,
as in a recent example from Craig Ringer.  We can also get rid of an
ugly kluge that represented lists of TransactionIds as lists of OIDs.

Heikki Linnakangas
This commit is contained in:
Tom Lane 2008-03-17 02:18:55 +00:00
parent a7c58abeb1
commit 32846f8152
3 changed files with 128 additions and 72 deletions
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3
src/backend/access/transam/twophase.c
View File

@ -7,7 +7,7 @@
* Portions Copyright (c) 1994, Regents of the University of California
*
* IDENTIFICATION
* $PostgreSQL: pgsql/src/backend/access/transam/twophase.c,v 1.39 2008/01/01 19:45:48 momjian Exp $
* $PostgreSQL: pgsql/src/backend/access/transam/twophase.c,v 1.40 2008/03/17 02:18:55 tgl Exp $
*
* NOTES
* Each global transaction is associated with a global transaction
@ -827,7 +827,6 @@ StartPrepare(GlobalTransaction gxact)
save_state_data(children, hdr.nsubxacts * sizeof(TransactionId));
/* While we have the child-xact data, stuff it in the gxact too */
GXactLoadSubxactData(gxact, hdr.nsubxacts, children);
pfree(children);
}
if (hdr.ncommitrels > 0)
{

184
src/backend/access/transam/xact.c
View File

@ -10,7 +10,7 @@
*
*
* IDENTIFICATION
* $PostgreSQL: pgsql/src/backend/access/transam/xact.c,v 1.258 2008/03/04 19:54:06 tgl Exp $
* $PostgreSQL: pgsql/src/backend/access/transam/xact.c,v 1.259 2008/03/17 02:18:55 tgl Exp $
*
*-------------------------------------------------------------------------
*/
@ -130,7 +130,9 @@ typedef struct TransactionStateData
int gucNestLevel; /* GUC context nesting depth */
MemoryContext curTransactionContext; /* my xact-lifetime context */
ResourceOwner curTransactionOwner; /* my query resources */
List *childXids; /* subcommitted child XIDs */
TransactionId *childXids; /* subcommitted child XIDs, in XID order */
int nChildXids; /* # of subcommitted child XIDs */
int maxChildXids; /* allocated size of childXids[] */
Oid prevUser; /* previous CurrentUserId setting */
bool prevSecDefCxt; /* previous SecurityDefinerContext setting */
bool prevXactReadOnly; /* entry-time xact r/o state */
@ -156,7 +158,9 @@ static TransactionStateData TopTransactionStateData = {
0, /* GUC context nesting depth */
NULL, /* cur transaction context */
NULL, /* cur transaction resource owner */
NIL, /* subcommitted child Xids */
NULL, /* subcommitted child Xids */
0, /* # of subcommitted child Xids */
0, /* allocated size of childXids[] */
InvalidOid, /* previous CurrentUserId setting */
false, /* previous SecurityDefinerContext setting */
false, /* entry-time xact r/o state */
@ -559,7 +563,7 @@ TransactionIdIsCurrentTransactionId(TransactionId xid)
*/
for (s = CurrentTransactionState; s != NULL; s = s->parent)
{
ListCell *cell;
int low, high;
if (s->state == TRANS_ABORT)
continue;
@ -567,10 +571,22 @@ TransactionIdIsCurrentTransactionId(TransactionId xid)
continue; /* it can't have any child XIDs either */
if (TransactionIdEquals(xid, s->transactionId))
return true;
foreach(cell, s->childXids)
/* As the childXids array is ordered, we can use binary search */
low = 0;
high = s->nChildXids - 1;
while (low <= high)
{
if (TransactionIdEquals(xid, lfirst_xid(cell)))
int middle;
TransactionId probe;
middle = low + (high - low) / 2;
probe = s->childXids[middle];
if (TransactionIdEquals(probe, xid))
return true;
else if (TransactionIdPrecedes(probe, xid))
low = middle + 1;
else
high = middle - 1;
}
}
@ -985,8 +1001,6 @@ cleanup:
/* Clean up local data */
if (rels)
pfree(rels);
if (children)
pfree(children);
return latestXid;
}
@ -1067,34 +1081,79 @@ static void
AtSubCommit_childXids(void)
{
TransactionState s = CurrentTransactionState;
MemoryContext old_cxt;
int new_nChildXids;
Assert(s->parent != NULL);
/*
* We keep the child-XID lists in TopTransactionContext; this avoids
* setting up child-transaction contexts for what might be just a few
* bytes of grandchild XIDs.
* The parent childXids array will need to hold my XID and all my
* childXids, in addition to the XIDs already there.
*/
old_cxt = MemoryContextSwitchTo(TopTransactionContext);
new_nChildXids = s->parent->nChildXids + s->nChildXids + 1;
s->parent->childXids = lappend_xid(s->parent->childXids,
s->transactionId);
if (s->childXids != NIL)
/* Allocate or enlarge the parent array if necessary */
if (s->parent->maxChildXids < new_nChildXids)
{
s->parent->childXids = list_concat(s->parent->childXids,
s->childXids);
int new_maxChildXids;
TransactionId *new_childXids;
/*
* list_concat doesn't free the list header for the second list; do so
* here to avoid memory leakage (kluge)
* Make it 2x what's needed right now, to avoid having to enlarge it
* repeatedly. But we can't go above MaxAllocSize. (The latter
* limit is what ensures that we don't need to worry about integer
* overflow here or in the calculation of new_nChildXids.)
*/
pfree(s->childXids);
s->childXids = NIL;
new_maxChildXids = Min(new_nChildXids * 2,
(int) (MaxAllocSize / sizeof(TransactionId)));
if (new_maxChildXids < new_nChildXids)
ereport(ERROR,
(errcode(ERRCODE_PROGRAM_LIMIT_EXCEEDED),
errmsg("maximum number of committed subtransactions (%d) exceeded",
(int) (MaxAllocSize / sizeof(TransactionId)))));
/*
* We keep the child-XID arrays in TopTransactionContext; this avoids
* setting up child-transaction contexts for what might be just a few
* bytes of grandchild XIDs.
*/
if (s->parent->childXids == NULL)
new_childXids =
MemoryContextAlloc(TopTransactionContext,
new_maxChildXids * sizeof(TransactionId));
else
new_childXids = repalloc(s->parent->childXids,
new_maxChildXids * sizeof(TransactionId));
s->parent->childXids = new_childXids;
s->parent->maxChildXids = new_maxChildXids;
}
MemoryContextSwitchTo(old_cxt);
/*
* Copy all my XIDs to parent's array.
*
* Note: We rely on the fact that the XID of a child always follows that
* of its parent. By copying the XID of this subtransaction before the
* XIDs of its children, we ensure that the array stays ordered. Likewise,
* all XIDs already in the array belong to subtransactions started and
* subcommitted before us, so their XIDs must precede ours.
*/
s->parent->childXids[s->parent->nChildXids] = s->transactionId;
if (s->nChildXids > 0)
memcpy(&s->parent->childXids[s->parent->nChildXids + 1],
s->childXids,
s->nChildXids * sizeof(TransactionId));
s->parent->nChildXids = new_nChildXids;
/* Release child's array to avoid leakage */
if (s->childXids != NULL)
pfree(s->childXids);
/* We must reset these to avoid double-free if fail later in commit */
s->childXids = NULL;
s->nChildXids = 0;
s->maxChildXids = 0;
}
/*
@ -1259,8 +1318,6 @@ RecordTransactionAbort(bool isSubXact)
/* And clean up local data */
if (rels)
pfree(rels);
if (children)
pfree(children);
return latestXid;
}
@ -1332,12 +1389,15 @@ AtSubAbort_childXids(void)
TransactionState s = CurrentTransactionState;
/*
* We keep the child-XID lists in TopTransactionContext (see
* AtSubCommit_childXids). This means we'd better free the list
* We keep the child-XID arrays in TopTransactionContext (see
* AtSubCommit_childXids). This means we'd better free the array
* explicitly at abort to avoid leakage.
*/
list_free(s->childXids);
s->childXids = NIL;
if (s->childXids != NULL)
pfree(s->childXids);
s->childXids = NULL;
s->nChildXids = 0;
s->maxChildXids = 0;
}
/* ----------------------------------------------------------------
@ -1506,7 +1566,9 @@ StartTransaction(void)
*/
s->nestingLevel = 1;
s->gucNestLevel = 1;
s->childXids = NIL;
s->childXids = NULL;
s->nChildXids = 0;
s->maxChildXids = 0;
GetUserIdAndContext(&s->prevUser, &s->prevSecDefCxt);
/* SecurityDefinerContext should never be set outside a transaction */
Assert(!s->prevSecDefCxt);
@ -1702,7 +1764,9 @@ CommitTransaction(void)
s->subTransactionId = InvalidSubTransactionId;
s->nestingLevel = 0;
s->gucNestLevel = 0;
s->childXids = NIL;
s->childXids = NULL;
s->nChildXids = 0;
s->maxChildXids = 0;
/*
* done with commit processing, set current transaction state back to
@ -1931,7 +1995,9 @@ PrepareTransaction(void)
s->subTransactionId = InvalidSubTransactionId;
s->nestingLevel = 0;
s->gucNestLevel = 0;
s->childXids = NIL;
s->childXids = NULL;
s->nChildXids = 0;
s->maxChildXids = 0;
/*
* done with 1st phase commit processing, set current transaction state
@ -2101,7 +2167,9 @@ CleanupTransaction(void)
s->subTransactionId = InvalidSubTransactionId;
s->nestingLevel = 0;
s->gucNestLevel = 0;
s->childXids = NIL;
s->childXids = NULL;
s->nChildXids = 0;
s->maxChildXids = 0;
/*
* done with abort processing, set current transaction state back to
@ -4051,6 +4119,19 @@ ShowTransactionState(const char *str)
static void
ShowTransactionStateRec(TransactionState s)
{
StringInfoData buf;
initStringInfo(&buf);
if (s->nChildXids > 0)
{
int i;
appendStringInfo(&buf, "%u", s->childXids[0]);
for (i = 1; i < s->nChildXids; i++)
appendStringInfo(&buf, " %u", s->childXids[i]);
}
if (s->parent)
ShowTransactionStateRec(s->parent);
@ -4064,8 +4145,9 @@ ShowTransactionStateRec(TransactionState s)
(unsigned int) s->subTransactionId,
(unsigned int) currentCommandId,
currentCommandIdUsed ? " (used)" : "",
s->nestingLevel,
nodeToString(s->childXids))));
s->nestingLevel, buf.data)));
pfree(buf.data);
}
/*
@ -4144,36 +4226,22 @@ TransStateAsString(TransState state)
* xactGetCommittedChildren
*
* Gets the list of committed children of the current transaction. The return
* value is the number of child transactions. *children is set to point to a
* palloc'd array of TransactionIds. If there are no subxacts, *children is
* set to NULL.
* value is the number of child transactions. *ptr is set to point to an
* array of TransactionIds. The array is allocated in TopTransactionContext;
* the caller should *not* pfree() it (this is a change from pre-8.4 code!).
* If there are no subxacts, *ptr is set to NULL.
*/
int
xactGetCommittedChildren(TransactionId **ptr)
{
TransactionState s = CurrentTransactionState;
int nchildren;
TransactionId *children;
ListCell *p;
nchildren = list_length(s->childXids);
if (nchildren == 0)
{
if (s->nChildXids == 0)
*ptr = NULL;
return 0;
}
else
*ptr = s->childXids;
children = (TransactionId *) palloc(nchildren * sizeof(TransactionId));
*ptr = children;
foreach(p, s->childXids)
{
TransactionId child = lfirst_xid(p);
*children++ = child;
}
return nchildren;
return s->nChildXids;
}
/*

13
src/include/nodes/pg_list.h
View File

@ -26,16 +26,11 @@
* (At the moment, ints and Oids are the same size, but they may not
* always be so; try to be careful to maintain the distinction.)
*
* There is also limited support for lists of TransactionIds; since these
* are used in only one or two places, we don't provide a full implementation,
* but map them onto Oid lists. This effectively assumes that TransactionId
* is no wider than Oid and both are unsigned types.
*
*
* Portions Copyright (c) 1996-2008, PostgreSQL Global Development Group
* Portions Copyright (c) 1994, Regents of the University of California
*
* $PostgreSQL: pgsql/src/include/nodes/pg_list.h,v 1.57 2008/01/01 19:45:58 momjian Exp $
* $PostgreSQL: pgsql/src/include/nodes/pg_list.h,v 1.58 2008/03/17 02:18:55 tgl Exp $
*
*-------------------------------------------------------------------------
*/
@ -159,12 +154,6 @@ extern int list_length(List *l);
#define list_make3_oid(x1,x2,x3) lcons_oid(x1, list_make2_oid(x2, x3))
#define list_make4_oid(x1,x2,x3,x4) lcons_oid(x1, list_make3_oid(x2, x3, x4))
/*
* Limited support for lists of TransactionIds, mapped onto lists of Oids
*/
#define lfirst_xid(lc) ((TransactionId) lfirst_oid(lc))
#define lappend_xid(list, datum) lappend_oid(list, (Oid) (datum))
/*
* foreach -
* a convenience macro which loops through the list