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Implement lazy XID allocation: transactions that do not modify any database

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rows will normally never obtain an XID at all.  We already did things this way
for subtransactions, but this patch extends the concept to top-level
transactions.  In applications where there are lots of short read-only
transactions, this should improve performance noticeably; not so much from
removal of the actual XID-assignments, as from reduction of overhead that's
driven by the rate of XID consumption.  We add a concept of a "virtual
transaction ID" so that active transactions can be uniquely identified even
if they don't have a regular XID.  This is a much lighter-weight concept:
uniqueness of VXIDs is only guaranteed over the short term, and no on-disk
record is made about them.

Florian Pflug, with some editorialization by Tom.
This commit is contained in:
Tom Lane
2007-09-05 18:10:48 +00:00
parent 2e74c53ec1
commit 295e63983d
34 changed files with 1002 additions and 754 deletions
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96
src/backend/utils/adt/lockfuncs.c
View File

@ -6,7 +6,7 @@
* Copyright (c) 2002-2007, PostgreSQL Global Development Group
*
* IDENTIFICATION
* $PostgreSQL: pgsql/src/backend/utils/adt/lockfuncs.c,v 1.28 2007/01/05 22:19:41 momjian Exp $
* $PostgreSQL: pgsql/src/backend/utils/adt/lockfuncs.c,v 1.29 2007/09/05 18:10:48 tgl Exp $
*
*-------------------------------------------------------------------------
*/
@ -27,6 +27,7 @@ static const char *const LockTagTypeNames[] = {
"page",
"tuple",
"transactionid",
"virtualxid",
"object",
"userlock",
"advisory"
@ -39,6 +40,27 @@ typedef struct
int currIdx; /* current PROCLOCK index */
} PG_Lock_Status;
/*
* VXIDGetDatum - Construct a text representation of a VXID
*
* This is currently only used in pg_lock_status, so we put it here.
*/
static Datum
VXIDGetDatum(BackendId bid, LocalTransactionId lxid)
{
/*
* The representation is "<bid>/<lxid>", decimal and unsigned decimal
* respectively. Note that elog.c also knows how to format a vxid.
*/
char vxidstr[32];
snprintf(vxidstr, sizeof(vxidstr), "%d/%u", bid, lxid);
return DirectFunctionCall1(textin, CStringGetDatum(vxidstr));
}
/*
* pg_lock_status - produce a view with one row per held or awaited lock mode
*/
@ -64,7 +86,7 @@ pg_lock_status(PG_FUNCTION_ARGS)
/* build tupdesc for result tuples */
/* this had better match pg_locks view in system_views.sql */
tupdesc = CreateTemplateTupleDesc(13, false);
tupdesc = CreateTemplateTupleDesc(14, false);
TupleDescInitEntry(tupdesc, (AttrNumber) 1, "locktype",
TEXTOID, -1, 0);
TupleDescInitEntry(tupdesc, (AttrNumber) 2, "database",
@ -75,21 +97,23 @@ pg_lock_status(PG_FUNCTION_ARGS)
INT4OID, -1, 0);
TupleDescInitEntry(tupdesc, (AttrNumber) 5, "tuple",
INT2OID, -1, 0);
TupleDescInitEntry(tupdesc, (AttrNumber) 6, "transactionid",
XIDOID, -1, 0);
TupleDescInitEntry(tupdesc, (AttrNumber) 7, "classid",
OIDOID, -1, 0);
TupleDescInitEntry(tupdesc, (AttrNumber) 8, "objid",
OIDOID, -1, 0);
TupleDescInitEntry(tupdesc, (AttrNumber) 9, "objsubid",
INT2OID, -1, 0);
TupleDescInitEntry(tupdesc, (AttrNumber) 10, "transaction",
XIDOID, -1, 0);
TupleDescInitEntry(tupdesc, (AttrNumber) 11, "pid",
INT4OID, -1, 0);
TupleDescInitEntry(tupdesc, (AttrNumber) 12, "mode",
TupleDescInitEntry(tupdesc, (AttrNumber) 6, "virtualxid",
TEXTOID, -1, 0);
TupleDescInitEntry(tupdesc, (AttrNumber) 13, "granted",
TupleDescInitEntry(tupdesc, (AttrNumber) 7, "transactionid",
XIDOID, -1, 0);
TupleDescInitEntry(tupdesc, (AttrNumber) 8, "classid",
OIDOID, -1, 0);
TupleDescInitEntry(tupdesc, (AttrNumber) 9, "objid",
OIDOID, -1, 0);
TupleDescInitEntry(tupdesc, (AttrNumber) 10, "objsubid",
INT2OID, -1, 0);
TupleDescInitEntry(tupdesc, (AttrNumber) 11, "virtualtransaction",
TEXTOID, -1, 0);
TupleDescInitEntry(tupdesc, (AttrNumber) 12, "pid",
INT4OID, -1, 0);
TupleDescInitEntry(tupdesc, (AttrNumber) 13, "mode",
TEXTOID, -1, 0);
TupleDescInitEntry(tupdesc, (AttrNumber) 14, "granted",
BOOLOID, -1, 0);
funcctx->tuple_desc = BlessTupleDesc(tupdesc);
@ -120,8 +144,8 @@ pg_lock_status(PG_FUNCTION_ARGS)
LOCKMODE mode = 0;
const char *locktypename;
char tnbuf[32];
Datum values[13];
char nulls[13];
Datum values[14];
char nulls[14];
HeapTuple tuple;
Datum result;
@ -193,7 +217,6 @@ pg_lock_status(PG_FUNCTION_ARGS)
values[0] = DirectFunctionCall1(textin,
CStringGetDatum(locktypename));
switch (lock->tag.locktag_type)
{
case LOCKTAG_RELATION:
@ -206,6 +229,7 @@ pg_lock_status(PG_FUNCTION_ARGS)
nulls[6] = 'n';
nulls[7] = 'n';
nulls[8] = 'n';
nulls[9] = 'n';
break;
case LOCKTAG_PAGE:
values[1] = ObjectIdGetDatum(lock->tag.locktag_field1);
@ -216,6 +240,7 @@ pg_lock_status(PG_FUNCTION_ARGS)
nulls[6] = 'n';
nulls[7] = 'n';
nulls[8] = 'n';
nulls[9] = 'n';
break;
case LOCKTAG_TUPLE:
values[1] = ObjectIdGetDatum(lock->tag.locktag_field1);
@ -226,9 +251,22 @@ pg_lock_status(PG_FUNCTION_ARGS)
nulls[6] = 'n';
nulls[7] = 'n';
nulls[8] = 'n';
nulls[9] = 'n';
break;
case LOCKTAG_TRANSACTION:
values[5] = TransactionIdGetDatum(lock->tag.locktag_field1);
values[6] = TransactionIdGetDatum(lock->tag.locktag_field1);
nulls[1] = 'n';
nulls[2] = 'n';
nulls[3] = 'n';
nulls[4] = 'n';
nulls[5] = 'n';
nulls[7] = 'n';
nulls[8] = 'n';
nulls[9] = 'n';
break;
case LOCKTAG_VIRTUALTRANSACTION:
values[5] = VXIDGetDatum(lock->tag.locktag_field1,
lock->tag.locktag_field2);
nulls[1] = 'n';
nulls[2] = 'n';
nulls[3] = 'n';
@ -236,31 +274,33 @@ pg_lock_status(PG_FUNCTION_ARGS)
nulls[6] = 'n';
nulls[7] = 'n';
nulls[8] = 'n';
nulls[9] = 'n';
break;
case LOCKTAG_OBJECT:
case LOCKTAG_USERLOCK:
case LOCKTAG_ADVISORY:
default: /* treat unknown locktags like OBJECT */
values[1] = ObjectIdGetDatum(lock->tag.locktag_field1);
values[6] = ObjectIdGetDatum(lock->tag.locktag_field2);
values[7] = ObjectIdGetDatum(lock->tag.locktag_field3);
values[8] = Int16GetDatum(lock->tag.locktag_field4);
values[7] = ObjectIdGetDatum(lock->tag.locktag_field2);
values[8] = ObjectIdGetDatum(lock->tag.locktag_field3);
values[9] = Int16GetDatum(lock->tag.locktag_field4);
nulls[2] = 'n';
nulls[3] = 'n';
nulls[4] = 'n';
nulls[5] = 'n';
nulls[6] = 'n';
break;
}
values[9] = TransactionIdGetDatum(proc->xid);
values[10] = VXIDGetDatum(proc->backendId, proc->lxid);
if (proc->pid != 0)
values[10] = Int32GetDatum(proc->pid);
values[11] = Int32GetDatum(proc->pid);
else
nulls[10] = 'n';
values[11] = DirectFunctionCall1(textin,
nulls[11] = 'n';
values[12] = DirectFunctionCall1(textin,
CStringGetDatum(GetLockmodeName(LOCK_LOCKMETHOD(*lock),
mode)));
values[12] = BoolGetDatum(granted);
values[13] = BoolGetDatum(granted);
tuple = heap_formtuple(funcctx->tuple_desc, values, nulls);
result = HeapTupleGetDatum(tuple);