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Make the comments more clear on the fact that UpdateFullPageWrites() is not

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safe to call concurrently from multiple processes.
This commit is contained in:
Heikki Linnakangas
2012-03-06 10:44:51 +02:00
parent 7714c63829
commit e587e2e3e3
1 changed files with 5 additions and 3 deletions
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8
src/backend/access/transam/xlog.c
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@ -8442,6 +8442,9 @@ XLogReportParameters(void)
/* /*
* Update full_page_writes in shared memory, and write an * Update full_page_writes in shared memory, and write an
* XLOG_FPW_CHANGE record if necessary. * XLOG_FPW_CHANGE record if necessary.
*
* Note: this function assumes there is no other process running
* concurrently that could update it.
*/ */
void void
UpdateFullPageWrites(void) UpdateFullPageWrites(void)
@ -8452,8 +8455,8 @@ UpdateFullPageWrites(void)
* Do nothing if full_page_writes has not been changed. * Do nothing if full_page_writes has not been changed.
* *
* It's safe to check the shared full_page_writes without the lock, * It's safe to check the shared full_page_writes without the lock,
* because we can guarantee that there is no concurrently running * because we assume that there is no concurrently running process
* process which can update it. * which can update it.
*/ */
if (fullPageWrites == Insert->fullPageWrites) if (fullPageWrites == Insert->fullPageWrites)
return; return;
@ -8490,7 +8493,6 @@ UpdateFullPageWrites(void)
XLogInsert(RM_XLOG_ID, XLOG_FPW_CHANGE, &rdata); XLogInsert(RM_XLOG_ID, XLOG_FPW_CHANGE, &rdata);
} }
if (!fullPageWrites) if (!fullPageWrites)
{ {
LWLockAcquire(WALInsertLock, LW_EXCLUSIVE); LWLockAcquire(WALInsertLock, LW_EXCLUSIVE);