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Create a new dedicated Postgres process, "wal writer", which exists to write

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and fsync WAL at convenient intervals.  For the moment it just tries to
offload this work from backends, but soon it will be responsible for
guaranteeing a maximum delay before asynchronously-committed transactions
will be flushed to disk.

This is a portion of Simon Riggs' async-commit patch, committed to CVS
separately because a background WAL writer seems like it might be a good idea
independently of the async-commit feature.  I rebased walwriter.c on
bgwriter.c because it seemed like a more appropriate way of handling signals;
while the startup/shutdown logic in postmaster.c is more like autovac because
we want walwriter to quit before we start the shutdown checkpoint.
This commit is contained in:
Tom Lane
2007-07-24 04:54:09 +00:00
parent 53d2951be7
commit ad4295728e
11 changed files with 547 additions and 70 deletions
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14
src/backend/bootstrap/bootstrap.c
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@ -8,7 +8,7 @@
* Portions Copyright (c) 1994, Regents of the University of California
*
* IDENTIFICATION
* $PostgreSQL: pgsql/src/backend/bootstrap/bootstrap.c,v 1.234 2007/06/28 00:02:37 tgl Exp $
* $PostgreSQL: pgsql/src/backend/bootstrap/bootstrap.c,v 1.235 2007/07/24 04:54:09 tgl Exp $
*
*-------------------------------------------------------------------------
*/
@ -30,6 +30,7 @@
#include "miscadmin.h"
#include "nodes/makefuncs.h"
#include "postmaster/bgwriter.h"
#include "postmaster/walwriter.h"
#include "storage/freespace.h"
#include "storage/ipc.h"
#include "storage/proc.h"
@ -195,7 +196,7 @@ static IndexList *ILHead = NULL;
* AuxiliaryProcessMain
*
* The main entry point for auxiliary processes, such as the bgwriter,
* bootstrapper and the shared memory checker code.
* walwriter, bootstrapper and the shared memory checker code.
*
* This code is here just because of historical reasons.
*/
@ -331,6 +332,9 @@ AuxiliaryProcessMain(int argc, char *argv[])
case BgWriterProcess:
statmsg = "writer process";
break;
case WalWriterProcess:
statmsg = "wal writer process";
break;
default:
statmsg = "??? process";
break;
@ -419,6 +423,12 @@ AuxiliaryProcessMain(int argc, char *argv[])
InitXLOGAccess();
BackgroundWriterMain();
proc_exit(1); /* should never return */
case WalWriterProcess:
/* don't set signals, walwriter has its own agenda */
InitXLOGAccess();
WalWriterMain();
proc_exit(1); /* should never return */
default:
elog(PANIC, "unrecognized process type: %d", auxType);