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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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24
src/backend/access/heap/heapam.c
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@ -8,7 +8,7 @@
*
*
* IDENTIFICATION
* $PostgreSQL: pgsql/src/backend/access/heap/heapam.c,v 1.237 2007/08/14 17:35:18 tgl Exp $
* $PostgreSQL: pgsql/src/backend/access/heap/heapam.c,v 1.238 2007/09/05 18:10:47 tgl Exp $
*
*
* INTERFACE ROUTINES
@ -1632,12 +1632,7 @@ heap_insert(Relation relation, HeapTuple tup, CommandId cid,
MarkBufferDirty(buffer);
/* XLOG stuff */
if (relation->rd_istemp)
{
/* No XLOG record, but still need to flag that XID exists on disk */
MyXactMadeTempRelUpdate = true;
}
else if (use_wal)
if (use_wal && !relation->rd_istemp)
{
xl_heap_insert xlrec;
xl_heap_header xlhdr;
@ -1947,11 +1942,6 @@ l1:
PageSetLSN(dp, recptr);
PageSetTLI(dp, ThisTimeLineID);
}
else
{
/* No XLOG record, but still need to flag that XID exists on disk */
MyXactMadeTempRelUpdate = true;
}
END_CRIT_SECTION();
@ -2403,11 +2393,6 @@ l2:
PageSetLSN(BufferGetPage(buffer), recptr);
PageSetTLI(BufferGetPage(buffer), ThisTimeLineID);
}
else
{
/* No XLOG record, but still need to flag that XID exists on disk */
MyXactMadeTempRelUpdate = true;
}
END_CRIT_SECTION();
@ -2924,11 +2909,6 @@ l3:
PageSetLSN(dp, recptr);
PageSetTLI(dp, ThisTimeLineID);
}
else
{
/* No XLOG record, but still need to flag that XID exists on disk */
MyXactMadeTempRelUpdate = true;
}
END_CRIT_SECTION();