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https://git.postgresql.org/git/postgresql.git
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Use O_DIRECT if available when using O_SYNC for wal_sync_method.
Also, write multiple WAL buffers out in one write() operation.
ITAGAKI Takahiro
---------------------------------------------------------------------------
> If we disable writeback-cache and use open_sync, the per-page writing
> behavior in WAL module will show up as bad result. O_DIRECT is similar
> to O_DSYNC (at least on linux), so that the benefit of it will disappear
> behind the slow disk revolution.
>
> In the current source, WAL is written as:
> for (i = 0; i < N; i++) { write(&buffers[i], BLCKSZ); }
> Is this intentional? Can we rewrite it as follows?
> write(&buffers[0], N * BLCKSZ);
>
> In order to achieve it, I wrote a 'gather-write' patch (xlog.gw.diff).
> Aside from this, I'll also send the fixed direct io patch (xlog.dio.diff).
> These two patches are independent, so they can be applied either or both.
>
>
> I tested them on my machine and the results as follows. It shows that
> direct-io and gather-write is the best choice when writeback-cache is off.
> Are these two patches worth trying if they are used together?
>
>
> | writeback | fsync= | fdata | open_ | fsync_ | open_
> patch | cache | false | sync | sync | direct | direct
> ------------+-----------+--------+-------+-------+--------+---------
> direct io | off | 124.2 | 105.7 | 48.3 | 48.3 | 48.2
> direct io | on | 129.1 | 112.3 | 114.1 | 142.9 | 144.5
> gather-write| off | 124.3 | 108.7 | 105.4 | (N/A) | (N/A)
> both | off | 131.5 | 115.5 | 114.4 | 145.4 | 145.2
>
> - 20runs * pgbench -s 100 -c 50 -t 200
> - with tuning (wal_buffers=64, commit_delay=500, checkpoint_segments=8)
> - using 2 ATA disks:
> - hda(reiserfs) includes system and wal.
> - hdc(jfs) includes database files. writeback-cache is always on.
>
> ---
> ITAGAKI Takahiro
This commit is contained in:
Bruce Momjian
parent
722f31f786
commit
c34bb00581
@ -7,7 +7,7 @@
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* Portions Copyright (c) 1996-2005, PostgreSQL Global Development Group
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* Portions Copyright (c) 1994, Regents of the University of California
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*
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* $PostgreSQL: pgsql/src/backend/access/transam/xlog.c,v 1.210 2005/07/23 15:31:16 momjian Exp $
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* $PostgreSQL: pgsql/src/backend/access/transam/xlog.c,v 1.211 2005/07/29 03:22:33 momjian Exp $
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*
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*-------------------------------------------------------------------------
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*/
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@ -47,6 +47,20 @@
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#include "utils/relcache.h"
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/*
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* Becauase O_DIRECT bypasses the kernel buffers, and because we never
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* read those buffers except during crash recovery, it is a win to use
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* it in all cases where we sync on each write(). We could allow O_DIRECT
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* with fsync(), but because skipping the kernel buffer forces writes out
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* quickly, it seems best just to use it for O_SYNC. It is hard to imagine
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* how fsync() could be a win for O_DIRECT compared to O_SYNC and O_DIRECT.
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*/
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#ifdef O_DIRECT
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#define PG_O_DIRECT O_DIRECT
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#else
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#define PG_O_DIRECT 0
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#endif
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/*
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* This chunk of hackery attempts to determine which file sync methods
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* are available on the current platform, and to choose an appropriate
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@ -54,24 +68,50 @@
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* configure determined whether fdatasync() is.
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*/
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#if defined(O_SYNC)
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#define OPEN_SYNC_FLAG O_SYNC
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#define CMP_OPEN_SYNC_FLAG O_SYNC
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#else
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#if defined(O_FSYNC)
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#define OPEN_SYNC_FLAG O_FSYNC
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#define CMP_OPEN_SYNC_FLAG O_FSYNC
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#endif
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#endif
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#define OPEN_SYNC_FLAG (CMP_OPEN_SYNC_FLAG | PG_O_DIRECT)
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#if defined(O_DSYNC)
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#if defined(OPEN_SYNC_FLAG)
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#if O_DSYNC != OPEN_SYNC_FLAG
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#define OPEN_DATASYNC_FLAG O_DSYNC
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#if O_DSYNC != CMP_OPEN_SYNC_FLAG
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#define OPEN_DATASYNC_FLAG (O_DSYNC | PG_O_DIRECT)
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#endif
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#else /* !defined(OPEN_SYNC_FLAG) */
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/* Win32 only has O_DSYNC */
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#define OPEN_DATASYNC_FLAG O_DSYNC
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#define OPEN_DATASYNC_FLAG (O_DSYNC | PG_O_DIRECT)
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#endif
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#endif
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/*
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* Limitation of buffer-alignment for direct io depend on OS and filesystem,
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* but BLCKSZ is assumed to be enough for it.
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*/
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#ifdef O_DIRECT
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#define ALIGNOF_XLOG_BUFFER BLCKSZ
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#else
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#define ALIGNOF_XLOG_BUFFER MAXIMUM_ALIGNOF
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#endif
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/*
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* Switch the alignment routine because ShmemAlloc() returns a max-aligned
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* buffer and ALIGNOF_XLOG_BUFFER may be greater than MAXIMUM_ALIGNOF.
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*/
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#if ALIGNOF_XLOG_BUFFER <= MAXIMUM_ALIGNOF
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#define XLOG_BUFFER_ALIGN(LEN) MAXALIGN((LEN))
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#else
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#define XLOG_BUFFER_ALIGN(LEN) ((LEN) + (ALIGNOF_XLOG_BUFFER))
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#endif
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/* assume sizeof(ptrdiff_t) == sizeof(void*) */
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#define POINTERALIGN(ALIGNVAL,PTR) \
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((char *)(((ptrdiff_t) (PTR) + (ALIGNVAL-1)) & ~((ptrdiff_t) (ALIGNVAL-1))))
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#define XLOG_BUFFER_POINTERALIGN(PTR) \
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POINTERALIGN((ALIGNOF_XLOG_BUFFER), (PTR))
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#if defined(OPEN_DATASYNC_FLAG)
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#define DEFAULT_SYNC_METHOD_STR "open_datasync"
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#define DEFAULT_SYNC_METHOD SYNC_METHOD_OPEN
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@ -469,6 +509,17 @@ static void ReadControlFile(void);
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static char *str_time(time_t tnow);
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static void issue_xlog_fsync(void);
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/* XLog gather-write staffs */
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typedef struct XLogPages
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{
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char *head; /* Head of first page */
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int size; /* Total bytes of pages == count(pages) * BLCKSZ */
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int offset; /* Offset in xlog segment file */
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} XLogPages;
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static void XLogPageReset(XLogPages *pages);
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static void XLogPageWrite(XLogPages *pages, int index);
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static void XLogPageFlush(XLogPages *pages, int index);
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#ifdef WAL_DEBUG
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static void xlog_outrec(char *buf, XLogRecord *record);
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#endif
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@ -1245,9 +1296,10 @@ static void
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XLogWrite(XLogwrtRqst WriteRqst)
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{
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XLogCtlWrite *Write = &XLogCtl->Write;
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char *from;
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bool ispartialpage;
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bool use_existent;
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int currentIndex = Write->curridx;
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XLogPages pages;
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/* We should always be inside a critical section here */
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Assert(CritSectionCount > 0);
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@ -1258,6 +1310,8 @@ XLogWrite(XLogwrtRqst WriteRqst)
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*/
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LogwrtResult = Write->LogwrtResult;
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XLogPageReset(&pages);
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while (XLByteLT(LogwrtResult.Write, WriteRqst.Write))
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{
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/*
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@ -1266,14 +1320,14 @@ XLogWrite(XLogwrtRqst WriteRqst)
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* end of the last page that's been initialized by
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* AdvanceXLInsertBuffer.
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*/
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if (!XLByteLT(LogwrtResult.Write, XLogCtl->xlblocks[Write->curridx]))
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if (!XLByteLT(LogwrtResult.Write, XLogCtl->xlblocks[currentIndex]))
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elog(PANIC, "xlog write request %X/%X is past end of log %X/%X",
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LogwrtResult.Write.xlogid, LogwrtResult.Write.xrecoff,
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XLogCtl->xlblocks[Write->curridx].xlogid,
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XLogCtl->xlblocks[Write->curridx].xrecoff);
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XLogCtl->xlblocks[currentIndex].xlogid,
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XLogCtl->xlblocks[currentIndex].xrecoff);
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/* Advance LogwrtResult.Write to end of current buffer page */
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LogwrtResult.Write = XLogCtl->xlblocks[Write->curridx];
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LogwrtResult.Write = XLogCtl->xlblocks[currentIndex];
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ispartialpage = XLByteLT(WriteRqst.Write, LogwrtResult.Write);
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if (!XLByteInPrevSeg(LogwrtResult.Write, openLogId, openLogSeg))
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@ -1281,6 +1335,7 @@ XLogWrite(XLogwrtRqst WriteRqst)
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/*
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* Switch to new logfile segment.
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*/
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XLogPageFlush(&pages, currentIndex);
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if (openLogFile >= 0)
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{
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if (close(openLogFile))
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@ -1354,31 +1409,8 @@ XLogWrite(XLogwrtRqst WriteRqst)
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openLogOff = 0;
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}
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/* Need to seek in the file? */
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if (openLogOff != (LogwrtResult.Write.xrecoff - BLCKSZ) % XLogSegSize)
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{
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openLogOff = (LogwrtResult.Write.xrecoff - BLCKSZ) % XLogSegSize;
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if (lseek(openLogFile, (off_t) openLogOff, SEEK_SET) < 0)
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ereport(PANIC,
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(errcode_for_file_access(),
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errmsg("could not seek in log file %u, segment %u to offset %u: %m",
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openLogId, openLogSeg, openLogOff)));
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}
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/* OK to write the page */
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from = XLogCtl->pages + Write->curridx * BLCKSZ;
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errno = 0;
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if (write(openLogFile, from, BLCKSZ) != BLCKSZ)
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{
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/* if write didn't set errno, assume problem is no disk space */
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if (errno == 0)
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errno = ENOSPC;
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ereport(PANIC,
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(errcode_for_file_access(),
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errmsg("could not write to log file %u, segment %u at offset %u: %m",
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openLogId, openLogSeg, openLogOff)));
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}
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openLogOff += BLCKSZ;
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/* Add a page to buffer */
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XLogPageWrite(&pages, currentIndex);
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/*
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* If we just wrote the whole last page of a logfile segment,
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@ -1390,8 +1422,9 @@ XLogWrite(XLogwrtRqst WriteRqst)
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* This is also the right place to notify the Archiver that the
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* segment is ready to copy to archival storage.
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*/
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if (openLogOff >= XLogSegSize && !ispartialpage)
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if (openLogOff + pages.size >= XLogSegSize && !ispartialpage)
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{
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XLogPageFlush(&pages, currentIndex);
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issue_xlog_fsync();
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LogwrtResult.Flush = LogwrtResult.Write; /* end of current page */
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@ -1405,8 +1438,9 @@ XLogWrite(XLogwrtRqst WriteRqst)
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LogwrtResult.Write = WriteRqst.Write;
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break;
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}
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Write->curridx = NextBufIdx(Write->curridx);
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currentIndex = NextBufIdx(currentIndex);
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}
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XLogPageFlush(&pages, currentIndex);
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/*
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* If asked to flush, do so
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@ -3584,7 +3618,7 @@ XLOGShmemSize(void)
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if (XLOGbuffers < MinXLOGbuffers)
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XLOGbuffers = MinXLOGbuffers;
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return MAXALIGN(sizeof(XLogCtlData) + sizeof(XLogRecPtr) * XLOGbuffers)
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return XLOG_BUFFER_ALIGN(sizeof(XLogCtlData) + sizeof(XLogRecPtr) * XLOGbuffers)
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+ BLCKSZ * XLOGbuffers +
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MAXALIGN(sizeof(ControlFileData));
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}
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@ -3601,7 +3635,7 @@ XLOGShmemInit(void)
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XLogCtl = (XLogCtlData *)
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ShmemInitStruct("XLOG Ctl",
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MAXALIGN(sizeof(XLogCtlData) +
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XLOG_BUFFER_ALIGN(sizeof(XLogCtlData) +
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sizeof(XLogRecPtr) * XLOGbuffers)
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+ BLCKSZ * XLOGbuffers,
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&foundXLog);
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@ -3630,9 +3664,9 @@ XLOGShmemInit(void)
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* Here, on the other hand, we must MAXALIGN to ensure the page
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* buffers have worst-case alignment.
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*/
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XLogCtl->pages =
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((char *) XLogCtl) + MAXALIGN(sizeof(XLogCtlData) +
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sizeof(XLogRecPtr) * XLOGbuffers);
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XLogCtl->pages = XLOG_BUFFER_POINTERALIGN(
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((char *) XLogCtl)
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+ sizeof(XLogCtlData) + sizeof(XLogRecPtr) * XLOGbuffers);
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memset(XLogCtl->pages, 0, BLCKSZ * XLOGbuffers);
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/*
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@ -3690,10 +3724,9 @@ BootStrapXLOG(void)
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/* First timeline ID is always 1 */
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ThisTimeLineID = 1;
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/* Use malloc() to ensure buffer is MAXALIGNED */
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buffer = (char *) malloc(BLCKSZ);
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page = (XLogPageHeader) buffer;
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memset(buffer, 0, BLCKSZ);
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buffer = (char *) malloc(BLCKSZ + ALIGNOF_XLOG_BUFFER);
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page = (XLogPageHeader) XLOG_BUFFER_POINTERALIGN(buffer);
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memset(page, 0, BLCKSZ);
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/* Set up information for the initial checkpoint record */
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checkPoint.redo.xlogid = 0;
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@ -3745,7 +3778,7 @@ BootStrapXLOG(void)
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/* Write the first page with the initial record */
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errno = 0;
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if (write(openLogFile, buffer, BLCKSZ) != BLCKSZ)
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if (write(openLogFile, page, BLCKSZ) != BLCKSZ)
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{
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/* if write didn't set errno, assume problem is no disk space */
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if (errno == 0)
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@ -5837,3 +5870,71 @@ remove_backup_label(void)
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errmsg("could not remove file \"%s\": %m",
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BACKUP_LABEL_FILE)));
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}
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/* XLog gather-write staffs */
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static void
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XLogPageReset(XLogPages *pages)
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{
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memset(pages, 0, sizeof(*pages));
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}
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static void
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XLogPageWrite(XLogPages *pages, int index)
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{
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char *page = XLogCtl->pages + index * BLCKSZ;
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int size = BLCKSZ;
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int offset = (LogwrtResult.Write.xrecoff - BLCKSZ) % XLogSegSize;
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if (pages->head + pages->size == page
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&& pages->offset + pages->size == offset)
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{ /* Pages are continuous. Append new page. */
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pages->size += size;
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}
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else
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{ /* Pages are not continuous. Flush and clear. */
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XLogPageFlush(pages, PrevBufIdx(index));
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pages->head = page;
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pages->size = size;
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pages->offset = offset;
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}
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}
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static void
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XLogPageFlush(XLogPages *pages, int index)
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{
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if (!pages->head)
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{ /* No needs to write pages. */
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XLogCtl->Write.curridx = index;
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return;
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}
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/* Need to seek in the file? */
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if (openLogOff != pages->offset)
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{
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openLogOff = pages->offset;
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if (lseek(openLogFile, (off_t) openLogOff, SEEK_SET) < 0)
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ereport(PANIC,
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(errcode_for_file_access(),
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errmsg("could not seek in log file %u, segment %u to offset %u: %m",
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openLogId, openLogSeg, openLogOff)));
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}
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/* OK to write the page */
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errno = 0;
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if (write(openLogFile, pages->head, pages->size) != pages->size)
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{
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/* if write didn't set errno, assume problem is no disk space */
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if (errno == 0)
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errno = ENOSPC;
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ereport(PANIC,
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(errcode_for_file_access(),
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errmsg("could not write to log file %u, segment %u at offset %u: %m",
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openLogId, openLogSeg, openLogOff)));
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}
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openLogOff += pages->size;
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XLogCtl->Write.curridx = index;
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XLogPageReset(pages);
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}
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