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Support an optional asynchronous commit mode, in which we don't flush WAL

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before reporting a transaction committed.  Data consistency is still
guaranteed (unlike setting fsync = off), but a crash may lose the effects
of the last few transactions.  Patch by Simon, some editorialization by Tom.
This commit is contained in:
Tom Lane
2007-08-01 22:45:09 +00:00
parent c722628a43
commit 4a78cdeb6b
25 changed files with 998 additions and 303 deletions
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48
src/backend/access/transam/xlog.c
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@ -7,7 +7,7 @@
* Portions Copyright (c) 1996-2007, PostgreSQL Global Development Group
* Portions Copyright (c) 1994, Regents of the University of California
*
* $PostgreSQL: pgsql/src/backend/access/transam/xlog.c,v 1.275 2007/07/24 04:54:08 tgl Exp $
* $PostgreSQL: pgsql/src/backend/access/transam/xlog.c,v 1.276 2007/08/01 22:45:08 tgl Exp $
*
*-------------------------------------------------------------------------
*/
@ -305,6 +305,7 @@ typedef struct XLogCtlData
XLogwrtResult LogwrtResult;
uint32 ckptXidEpoch; /* nextXID & epoch of latest checkpoint */
TransactionId ckptXid;
XLogRecPtr asyncCommitLSN; /* LSN of newest async commit */
/* Protected by WALWriteLock: */
XLogCtlWrite Write;
@ -1643,6 +1644,22 @@ XLogWrite(XLogwrtRqst WriteRqst, bool flexible, bool xlog_switch)
Write->LogwrtResult = LogwrtResult;
}
/*
* Record the LSN for an asynchronous transaction commit.
* (This should not be called for aborts, nor for synchronous commits.)
*/
void
XLogSetAsyncCommitLSN(XLogRecPtr asyncCommitLSN)
{
/* use volatile pointer to prevent code rearrangement */
volatile XLogCtlData *xlogctl = XLogCtl;
SpinLockAcquire(&xlogctl->info_lck);
if (XLByteLT(xlogctl->asyncCommitLSN, asyncCommitLSN))
xlogctl->asyncCommitLSN = asyncCommitLSN;
SpinLockRelease(&xlogctl->info_lck);
}
/*
* Ensure that all XLOG data through the given position is flushed to disk.
*
@ -1797,19 +1814,17 @@ XLogBackgroundFlush(void)
/* back off to last completed page boundary */
WriteRqstPtr.xrecoff -= WriteRqstPtr.xrecoff % XLOG_BLCKSZ;
#ifdef NOT_YET /* async commit patch is still to come */
/* if we have already flushed that far, consider async commit records */
if (XLByteLE(WriteRqstPtr, LogwrtResult.Flush))
{
/* use volatile pointer to prevent code rearrangement */
volatile XLogCtlData *xlogctl = XLogCtl;
SpinLockAcquire(&xlogctl->async_commit_lck);
SpinLockAcquire(&xlogctl->info_lck);
WriteRqstPtr = xlogctl->asyncCommitLSN;
SpinLockRelease(&xlogctl->async_commit_lck);
SpinLockRelease(&xlogctl->info_lck);
flexible = false; /* ensure it all gets written */
}
#endif
/* Done if already known flushed */
if (XLByteLE(WriteRqstPtr, LogwrtResult.Flush))
@ -1841,6 +1856,23 @@ XLogBackgroundFlush(void)
END_CRIT_SECTION();
}
/*
* Flush any previous asynchronously-committed transactions' commit records.
*/
void
XLogAsyncCommitFlush(void)
{
XLogRecPtr WriteRqstPtr;
/* use volatile pointer to prevent code rearrangement */
volatile XLogCtlData *xlogctl = XLogCtl;
SpinLockAcquire(&xlogctl->info_lck);
WriteRqstPtr = xlogctl->asyncCommitLSN;
SpinLockRelease(&xlogctl->info_lck);
XLogFlush(WriteRqstPtr);
}
/*
* Test whether XLOG data has been flushed up to (at least) the given position.
*
@ -5466,7 +5498,7 @@ ShutdownXLOG(int code, Datum arg)
(errmsg("database system is shut down")));
}
/*
/*
* Log start of a checkpoint.
*/
static void
@ -5481,7 +5513,7 @@ LogCheckpointStart(int flags)
(flags & CHECKPOINT_CAUSE_TIME) ? " time" : "");
}
/*
/*
* Log end of a checkpoint.
*/
static void
@ -5523,7 +5555,7 @@ LogCheckpointEnd(void)
* flags is a bitwise OR of the following:
* CHECKPOINT_IS_SHUTDOWN: checkpoint is for database shutdown.
* CHECKPOINT_IMMEDIATE: finish the checkpoint ASAP,
* ignoring checkpoint_completion_target parameter.
* ignoring checkpoint_completion_target parameter.
* CHECKPOINT_FORCE: force a checkpoint even if no XLOG activity has occured
* since the last one (implied by CHECKPOINT_IS_SHUTDOWN).
*