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Don't use O_DIRECT when writing WAL files if archiving or streaming is

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enabled. Bypassing the kernel cache is counter-productive in that case,
because the archiver/walsender process will read from the WAL file
soon after it's written, and if it's not cached the read will cause
a physical read, eating I/O bandwidth available on the WAL drive.

Also, walreceiver process does unaligned writes, so disable O_DIRECT
in walreceiver process for that reason too.
This commit is contained in:
Heikki Linnakangas
2010-02-19 10:51:04 +00:00
parent 94f610b163
commit ad458cfe81
4 changed files with 48 additions and 27 deletions
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24
src/backend/replication/walreceiver.c
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@@ -29,7 +29,7 @@
*
*
* IDENTIFICATION
* $PostgreSQL: pgsql/src/backend/replication/walreceiver.c,v 1.4 2010/02/17 04:19:39 tgl Exp $
* $PostgreSQL: pgsql/src/backend/replication/walreceiver.c,v 1.5 2010/02/19 10:51:04 heikki Exp $
*
*-------------------------------------------------------------------------
*/
@@ -50,6 +50,9 @@
#include "utils/ps_status.h"
#include "utils/resowner.h"
/* Global variable to indicate if this process is a walreceiver process */
bool am_walreceiver;
/* libpqreceiver hooks to these when loaded */
walrcv_connect_type walrcv_connect = NULL;
walrcv_receive_type walrcv_receive = NULL;
@@ -158,6 +161,8 @@ WalReceiverMain(void)
/* use volatile pointer to prevent code rearrangement */
volatile WalRcvData *walrcv = WalRcv;
am_walreceiver = true;
/*
* WalRcv should be set up already (if we are a backend, we inherit
* this by fork() or EXEC_BACKEND mechanism from the postmaster).
@@ -424,16 +429,18 @@ XLogWalRcvWrite(char *buf, Size nbytes, XLogRecPtr recptr)
bool use_existent;
/*
* XLOG segment files will be re-read in recovery operation soon,
* so we don't need to advise the OS to release any cache page.
* fsync() and close current file before we switch to next one.
* We would otherwise have to reopen this file to fsync it later
*/
if (recvFile >= 0)
{
/*
* fsync() before we switch to next file. We would otherwise
* have to reopen this file to fsync it later
*/
XLogWalRcvFlush();
/*
* XLOG segment files will be re-read by recovery in startup
* process soon, so we don't advise the OS to release cache
* pages associated with the file like XLogFileClose() does.
*/
if (close(recvFile) != 0)
ereport(PANIC,
(errcode_for_file_access(),
@@ -445,8 +452,7 @@ XLogWalRcvWrite(char *buf, Size nbytes, XLogRecPtr recptr)
/* Create/use new log file */
XLByteToSeg(recptr, recvId, recvSeg);
use_existent = true;
recvFile = XLogFileInit(recvId, recvSeg,
&use_existent, true);
recvFile = XLogFileInit(recvId, recvSeg, &use_existent, true);
recvOff = 0;
}