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Reorder code so that we don't have to hold a critical section while 

reserving SLRU space for a new MultiXact.  The original coding would have
treated out-of-disk-space as a PANIC condition, which is unnecessary.
This commit is contained in:
Tom Lane 2005-10-28 19:00:19 +00:00
parent a7de22d8d5
commit a037926295
1 changed files with 28 additions and 24 deletions
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52
src/backend/access/transam/multixact.c
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@ -42,7 +42,7 @@
* Portions Copyright (c) 1996-2005, PostgreSQL Global Development Group
* Portions Copyright (c) 1994, Regents of the University of California
*
* $PostgreSQL: pgsql/src/backend/access/transam/multixact.c,v 1.10 2005/10/28 17:27:29 tgl Exp $
* $PostgreSQL: pgsql/src/backend/access/transam/multixact.c,v 1.11 2005/10/28 19:00:19 tgl Exp $
*
*-------------------------------------------------------------------------
*/
@ -630,22 +630,13 @@ CreateMultiXactId(int nxids, TransactionId *xids)
return multi;
}
/*
* Critical section from here until we've written the data; we don't
* want to error out with a partly written MultiXact structure.
* (In particular, failing to write our start offset after advancing
* nextMXact would effectively corrupt the previous MultiXact.)
*/
START_CRIT_SECTION();
/*
* Assign the MXID and offsets range to use, and make sure there is
* space in the OFFSETs and MEMBERs files.
* space in the OFFSETs and MEMBERs files. NB: this routine does
* START_CRIT_SECTION().
*/
multi = GetNewMultiXactId(nxids, &offset);
debug_elog4(DEBUG2, "Create: assigned id %u offset %u", multi, offset);
/*
* Make an XLOG entry describing the new MXID.
*
@ -768,6 +759,9 @@ RecordNewMultiXact(MultiXactId multi, MultiXactOffset offset,
* files. Unfortunately, we have to do that while holding MultiXactGenLock
* to avoid race conditions --- the XLOG record for zeroing a page must appear
* before any backend can possibly try to store data in that page!
*
* We start a critical section before advancing the shared counters. The
* caller must end the critical section after writing SLRU data.
*/
static MultiXactId
GetNewMultiXactId(int nxids, MultiXactOffset *offset)
@ -794,18 +788,7 @@ GetNewMultiXactId(int nxids, MultiXactOffset *offset)
ExtendMultiXactOffset(result);
/*
* Advance counter. As in GetNewTransactionId(), this must not happen
* until after ExtendMultiXactOffset has succeeded!
*
* We don't care about MultiXactId wraparound here; it will be handled by
* the next iteration. But note that nextMXact may be InvalidMultiXactId
* after this routine exits, so anyone else looking at the variable must
* be prepared to deal with that.
*/
(MultiXactState->nextMXact)++;
/*
* Reserve the members space. Same considerations as above. Also, be
* Reserve the members space, similarly to above. Also, be
* careful not to return zero as the starting offset for any multixact.
* See GetMultiXactIdMembers() for motivation.
*/
@ -820,6 +803,27 @@ GetNewMultiXactId(int nxids, MultiXactOffset *offset)
ExtendMultiXactMember(nextOffset, nxids);
/*
* Critical section from here until caller has written the data into
* the just-reserved SLRU space; we don't want to error out with a partly
* written MultiXact structure. (In particular, failing to write our
* start offset after advancing nextMXact would effectively corrupt the
* previous MultiXact.)
*/
START_CRIT_SECTION();
/*
* Advance counters. As in GetNewTransactionId(), this must not happen
* until after file extension has succeeded!
*
* We don't care about MultiXactId wraparound here; it will be handled by
* the next iteration. But note that nextMXact may be InvalidMultiXactId
* after this routine exits, so anyone else looking at the variable must
* be prepared to deal with that. Similarly, nextOffset may be zero,
* but we won't use that as the actual start offset of the next multixact.
*/
(MultiXactState->nextMXact)++;
MultiXactState->nextOffset += nxids;
LWLockRelease(MultiXactGenLock);