Re: [HACKERS] data on devel code perf dip

From: Mary Edie Meredith <maryedie(at)osdl(dot)org>
To: Bruce Momjian <pgman(at)candle(dot)pha(dot)pa(dot)us>
Cc: Mark Wong <markw(at)osdl(dot)org>, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>, Alvaro Herrera <alvherre(at)alvh(dot)no-ip(dot)org>, PostgreSQL-patches <pgsql-patches(at)postgresql(dot)org>, Josh Berkus <josh(at)agliodbs(dot)com>
Subject: Re: [HACKERS] data on devel code perf dip
Date: 2005-08-12 18:26:46
Message-ID: 1123871206.9956.113.camel@localhost
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Just to be certain I know what I have and how to use it,
please confirm the following is correct.

According to Markw, the tarball we have at OSDL that is
dated 7/29 already has the O_DIRECT patch + wal grouping
applied. Hence, I will use the one from the day before:
postgresql-20050728.tar.bz2 and apply your patch.

I expect to have, after applying the patch, the O_DIRECT patch
for the log (which I should not be using given the config
parameters I have), but I will _not have the wal grouping?

Is that correct?

On Fri, 2005-08-12 at 12:12 -0400, Bruce Momjian wrote:
> Mark Wong wrote:
> > On Thu, 11 Aug 2005 22:11:42 -0400 (EDT)
> > Bruce Momjian <pgman(at)candle(dot)pha(dot)pa(dot)us> wrote:
> >
> > > Tom Lane wrote:
> > > > Bruce Momjian <pgman(at)candle(dot)pha(dot)pa(dot)us> writes:
> > > > >> O_DIRECT is only being used for WAL page writes (or I sure hope so
> > > > >> anyway), so shared_buffers should be irrelevant.
> > > >
> > > > > Uh, O_DIRECT really just enables when open_sync is used, and I assume
> > > > > that is not used for writing dirty buffers during a checkpoint.
> > > >
> > > > I double-checked that O_DIRECT is really just used for WAL, and only
> > > > when the sync mode is open_sync or open_datasync. So it seems
> > > > impossible that it affected a run with mode fdatasync. What seems the
> > > > best theory at the moment is that the grouped-WAL-write part of the
> > > > patch doesn't work so well as we thought.
> > >
> > > Yes, that's my only guess. Let us know if you want the patch to test,
> > > rather than pulling CVS before and after the patch was applied.
> >
> > Yeah, a patch would be a little easier. :)
>
> OK, patch attached. The code has been cleaned up a little since then but
> this is the basic change that should be tested. It is based on CVS of
> 2005/07/29 03:22:33 GMT.
>
> Plain text document attachment (/bjm/diff)
> Index: src/backend/access/transam/xlog.c
> ===================================================================
> RCS file: /cvsroot/pgsql/src/backend/access/transam/xlog.c,v
> retrieving revision 1.210
> retrieving revision 1.211
> diff -c -r1.210 -r1.211
> *** src/backend/access/transam/xlog.c 23 Jul 2005 15:31:16 -0000 1.210
> --- src/backend/access/transam/xlog.c 29 Jul 2005 03:22:33 -0000 1.211
> ***************
> *** 48,77 ****
>
>
> /*
> * This chunk of hackery attempts to determine which file sync methods
> * are available on the current platform, and to choose an appropriate
> * default method. We assume that fsync() is always available, and that
> * configure determined whether fdatasync() is.
> */
> #if defined(O_SYNC)
> ! #define OPEN_SYNC_FLAG O_SYNC
> #else
> #if defined(O_FSYNC)
> ! #define OPEN_SYNC_FLAG O_FSYNC
> #endif
> #endif
>
> #if defined(O_DSYNC)
> #if defined(OPEN_SYNC_FLAG)
> ! #if O_DSYNC != OPEN_SYNC_FLAG
> ! #define OPEN_DATASYNC_FLAG O_DSYNC
> #endif
> #else /* !defined(OPEN_SYNC_FLAG) */
> /* Win32 only has O_DSYNC */
> ! #define OPEN_DATASYNC_FLAG O_DSYNC
> #endif
> #endif
>
> #if defined(OPEN_DATASYNC_FLAG)
> #define DEFAULT_SYNC_METHOD_STR "open_datasync"
> #define DEFAULT_SYNC_METHOD SYNC_METHOD_OPEN
> --- 48,117 ----
>
>
> /*
> + * Becauase O_DIRECT bypasses the kernel buffers, and because we never
> + * read those buffers except during crash recovery, it is a win to use
> + * it in all cases where we sync on each write(). We could allow O_DIRECT
> + * with fsync(), but because skipping the kernel buffer forces writes out
> + * quickly, it seems best just to use it for O_SYNC. It is hard to imagine
> + * how fsync() could be a win for O_DIRECT compared to O_SYNC and O_DIRECT.
> + */
> + #ifdef O_DIRECT
> + #define PG_O_DIRECT O_DIRECT
> + #else
> + #define PG_O_DIRECT 0
> + #endif
> +
> + /*
> * This chunk of hackery attempts to determine which file sync methods
> * are available on the current platform, and to choose an appropriate
> * default method. We assume that fsync() is always available, and that
> * configure determined whether fdatasync() is.
> */
> #if defined(O_SYNC)
> ! #define CMP_OPEN_SYNC_FLAG O_SYNC
> #else
> #if defined(O_FSYNC)
> ! #define CMP_OPEN_SYNC_FLAG O_FSYNC
> #endif
> #endif
> + #define OPEN_SYNC_FLAG (CMP_OPEN_SYNC_FLAG | PG_O_DIRECT)
>
> #if defined(O_DSYNC)
> #if defined(OPEN_SYNC_FLAG)
> ! #if O_DSYNC != CMP_OPEN_SYNC_FLAG
> ! #define OPEN_DATASYNC_FLAG (O_DSYNC | PG_O_DIRECT)
> #endif
> #else /* !defined(OPEN_SYNC_FLAG) */
> /* Win32 only has O_DSYNC */
> ! #define OPEN_DATASYNC_FLAG (O_DSYNC | PG_O_DIRECT)
> #endif
> #endif
>
> + /*
> + * Limitation of buffer-alignment for direct io depend on OS and filesystem,
> + * but BLCKSZ is assumed to be enough for it.
> + */
> + #ifdef O_DIRECT
> + #define ALIGNOF_XLOG_BUFFER BLCKSZ
> + #else
> + #define ALIGNOF_XLOG_BUFFER MAXIMUM_ALIGNOF
> + #endif
> +
> + /*
> + * Switch the alignment routine because ShmemAlloc() returns a max-aligned
> + * buffer and ALIGNOF_XLOG_BUFFER may be greater than MAXIMUM_ALIGNOF.
> + */
> + #if ALIGNOF_XLOG_BUFFER <= MAXIMUM_ALIGNOF
> + #define XLOG_BUFFER_ALIGN(LEN) MAXALIGN((LEN))
> + #else
> + #define XLOG_BUFFER_ALIGN(LEN) ((LEN) + (ALIGNOF_XLOG_BUFFER))
> + #endif
> + /* assume sizeof(ptrdiff_t) == sizeof(void*) */
> + #define POINTERALIGN(ALIGNVAL,PTR) \
> + ((char *)(((ptrdiff_t) (PTR) + (ALIGNVAL-1)) & ~((ptrdiff_t) (ALIGNVAL-1))))
> + #define XLOG_BUFFER_POINTERALIGN(PTR) \
> + POINTERALIGN((ALIGNOF_XLOG_BUFFER), (PTR))
> +
> #if defined(OPEN_DATASYNC_FLAG)
> #define DEFAULT_SYNC_METHOD_STR "open_datasync"
> #define DEFAULT_SYNC_METHOD SYNC_METHOD_OPEN
> ***************
> *** 469,474 ****
> --- 509,525 ----
> static char *str_time(time_t tnow);
> static void issue_xlog_fsync(void);
>
> + /* XLog gather-write staffs */
> + typedef struct XLogPages
> + {
> + char *head; /* Head of first page */
> + int size; /* Total bytes of pages == count(pages) * BLCKSZ */
> + int offset; /* Offset in xlog segment file */
> + } XLogPages;
> + static void XLogPageReset(XLogPages *pages);
> + static void XLogPageWrite(XLogPages *pages, int index);
> + static void XLogPageFlush(XLogPages *pages, int index);
> +
> #ifdef WAL_DEBUG
> static void xlog_outrec(char *buf, XLogRecord *record);
> #endif
> ***************
> *** 1245,1253 ****
> XLogWrite(XLogwrtRqst WriteRqst)
> {
> XLogCtlWrite *Write = &XLogCtl->Write;
> - char *from;
> bool ispartialpage;
> bool use_existent;
>
> /* We should always be inside a critical section here */
> Assert(CritSectionCount > 0);
> --- 1296,1305 ----
> XLogWrite(XLogwrtRqst WriteRqst)
> {
> XLogCtlWrite *Write = &XLogCtl->Write;
> bool ispartialpage;
> bool use_existent;
> + int currentIndex = Write->curridx;
> + XLogPages pages;
>
> /* We should always be inside a critical section here */
> Assert(CritSectionCount > 0);
> ***************
> *** 1258,1263 ****
> --- 1310,1317 ----
> */
> LogwrtResult = Write->LogwrtResult;
>
> + XLogPageReset(&pages);
> +
> while (XLByteLT(LogwrtResult.Write, WriteRqst.Write))
> {
> /*
> ***************
> *** 1266,1279 ****
> * end of the last page that's been initialized by
> * AdvanceXLInsertBuffer.
> */
> ! if (!XLByteLT(LogwrtResult.Write, XLogCtl->xlblocks[Write->curridx]))
> elog(PANIC, "xlog write request %X/%X is past end of log %X/%X",
> LogwrtResult.Write.xlogid, LogwrtResult.Write.xrecoff,
> ! XLogCtl->xlblocks[Write->curridx].xlogid,
> ! XLogCtl->xlblocks[Write->curridx].xrecoff);
>
> /* Advance LogwrtResult.Write to end of current buffer page */
> ! LogwrtResult.Write = XLogCtl->xlblocks[Write->curridx];
> ispartialpage = XLByteLT(WriteRqst.Write, LogwrtResult.Write);
>
> if (!XLByteInPrevSeg(LogwrtResult.Write, openLogId, openLogSeg))
> --- 1320,1333 ----
> * end of the last page that's been initialized by
> * AdvanceXLInsertBuffer.
> */
> ! if (!XLByteLT(LogwrtResult.Write, XLogCtl->xlblocks[currentIndex]))
> elog(PANIC, "xlog write request %X/%X is past end of log %X/%X",
> LogwrtResult.Write.xlogid, LogwrtResult.Write.xrecoff,
> ! XLogCtl->xlblocks[currentIndex].xlogid,
> ! XLogCtl->xlblocks[currentIndex].xrecoff);
>
> /* Advance LogwrtResult.Write to end of current buffer page */
> ! LogwrtResult.Write = XLogCtl->xlblocks[currentIndex];
> ispartialpage = XLByteLT(WriteRqst.Write, LogwrtResult.Write);
>
> if (!XLByteInPrevSeg(LogwrtResult.Write, openLogId, openLogSeg))
> ***************
> *** 1281,1286 ****
> --- 1335,1341 ----
> /*
> * Switch to new logfile segment.
> */
> + XLogPageFlush(&pages, currentIndex);
> if (openLogFile >= 0)
> {
> if (close(openLogFile))
> ***************
> *** 1354,1384 ****
> openLogOff = 0;
> }
>
> ! /* Need to seek in the file? */
> ! if (openLogOff != (LogwrtResult.Write.xrecoff - BLCKSZ) % XLogSegSize)
> ! {
> ! openLogOff = (LogwrtResult.Write.xrecoff - BLCKSZ) % XLogSegSize;
> ! if (lseek(openLogFile, (off_t) openLogOff, SEEK_SET) < 0)
> ! ereport(PANIC,
> ! (errcode_for_file_access(),
> ! errmsg("could not seek in log file %u, segment %u to offset %u: %m",
> ! openLogId, openLogSeg, openLogOff)));
> ! }
> !
> ! /* OK to write the page */
> ! from = XLogCtl->pages + Write->curridx * BLCKSZ;
> ! errno = 0;
> ! if (write(openLogFile, from, BLCKSZ) != BLCKSZ)
> ! {
> ! /* if write didn't set errno, assume problem is no disk space */
> ! if (errno == 0)
> ! errno = ENOSPC;
> ! ereport(PANIC,
> ! (errcode_for_file_access(),
> ! errmsg("could not write to log file %u, segment %u at offset %u: %m",
> ! openLogId, openLogSeg, openLogOff)));
> ! }
> ! openLogOff += BLCKSZ;
>
> /*
> * If we just wrote the whole last page of a logfile segment,
> --- 1409,1416 ----
> openLogOff = 0;
> }
>
> ! /* Add a page to buffer */
> ! XLogPageWrite(&pages, currentIndex);
>
> /*
> * If we just wrote the whole last page of a logfile segment,
> ***************
> *** 1390,1397 ****
> * This is also the right place to notify the Archiver that the
> * segment is ready to copy to archival storage.
> */
> ! if (openLogOff >= XLogSegSize && !ispartialpage)
> {
> issue_xlog_fsync();
> LogwrtResult.Flush = LogwrtResult.Write; /* end of current page */
>
> --- 1422,1430 ----
> * This is also the right place to notify the Archiver that the
> * segment is ready to copy to archival storage.
> */
> ! if (openLogOff + pages.size >= XLogSegSize && !ispartialpage)
> {
> + XLogPageFlush(&pages, currentIndex);
> issue_xlog_fsync();
> LogwrtResult.Flush = LogwrtResult.Write; /* end of current page */
>
> ***************
> *** 1405,1412 ****
> LogwrtResult.Write = WriteRqst.Write;
> break;
> }
> ! Write->curridx = NextBufIdx(Write->curridx);
> }
>
> /*
> * If asked to flush, do so
> --- 1438,1446 ----
> LogwrtResult.Write = WriteRqst.Write;
> break;
> }
> ! currentIndex = NextBufIdx(currentIndex);
> }
> + XLogPageFlush(&pages, currentIndex);
>
> /*
> * If asked to flush, do so
> ***************
> *** 3584,3590 ****
> if (XLOGbuffers < MinXLOGbuffers)
> XLOGbuffers = MinXLOGbuffers;
>
> ! return MAXALIGN(sizeof(XLogCtlData) + sizeof(XLogRecPtr) * XLOGbuffers)
> + BLCKSZ * XLOGbuffers +
> MAXALIGN(sizeof(ControlFileData));
> }
> --- 3618,3624 ----
> if (XLOGbuffers < MinXLOGbuffers)
> XLOGbuffers = MinXLOGbuffers;
>
> ! return XLOG_BUFFER_ALIGN(sizeof(XLogCtlData) + sizeof(XLogRecPtr) * XLOGbuffers)
> + BLCKSZ * XLOGbuffers +
> MAXALIGN(sizeof(ControlFileData));
> }
> ***************
> *** 3601,3607 ****
>
> XLogCtl = (XLogCtlData *)
> ShmemInitStruct("XLOG Ctl",
> ! MAXALIGN(sizeof(XLogCtlData) +
> sizeof(XLogRecPtr) * XLOGbuffers)
> + BLCKSZ * XLOGbuffers,
> &foundXLog);
> --- 3635,3641 ----
>
> XLogCtl = (XLogCtlData *)
> ShmemInitStruct("XLOG Ctl",
> ! XLOG_BUFFER_ALIGN(sizeof(XLogCtlData) +
> sizeof(XLogRecPtr) * XLOGbuffers)
> + BLCKSZ * XLOGbuffers,
> &foundXLog);
> ***************
> *** 3630,3638 ****
> * Here, on the other hand, we must MAXALIGN to ensure the page
> * buffers have worst-case alignment.
> */
> ! XLogCtl->pages =
> ! ((char *) XLogCtl) + MAXALIGN(sizeof(XLogCtlData) +
> ! sizeof(XLogRecPtr) * XLOGbuffers);
> memset(XLogCtl->pages, 0, BLCKSZ * XLOGbuffers);
>
> /*
> --- 3664,3672 ----
> * Here, on the other hand, we must MAXALIGN to ensure the page
> * buffers have worst-case alignment.
> */
> ! XLogCtl->pages = XLOG_BUFFER_POINTERALIGN(
> ! ((char *) XLogCtl)
> ! + sizeof(XLogCtlData) + sizeof(XLogRecPtr) * XLOGbuffers);
> memset(XLogCtl->pages, 0, BLCKSZ * XLOGbuffers);
>
> /*
> ***************
> *** 3690,3699 ****
> /* First timeline ID is always 1 */
> ThisTimeLineID = 1;
>
> ! /* Use malloc() to ensure buffer is MAXALIGNED */
> ! buffer = (char *) malloc(BLCKSZ);
> ! page = (XLogPageHeader) buffer;
> ! memset(buffer, 0, BLCKSZ);
>
> /* Set up information for the initial checkpoint record */
> checkPoint.redo.xlogid = 0;
> --- 3724,3732 ----
> /* First timeline ID is always 1 */
> ThisTimeLineID = 1;
>
> ! buffer = (char *) malloc(BLCKSZ + ALIGNOF_XLOG_BUFFER);
> ! page = (XLogPageHeader) XLOG_BUFFER_POINTERALIGN(buffer);
> ! memset(page, 0, BLCKSZ);
>
> /* Set up information for the initial checkpoint record */
> checkPoint.redo.xlogid = 0;
> ***************
> *** 3745,3751 ****
>
> /* Write the first page with the initial record */
> errno = 0;
> ! if (write(openLogFile, buffer, BLCKSZ) != BLCKSZ)
> {
> /* if write didn't set errno, assume problem is no disk space */
> if (errno == 0)
> --- 3778,3784 ----
>
> /* Write the first page with the initial record */
> errno = 0;
> ! if (write(openLogFile, page, BLCKSZ) != BLCKSZ)
> {
> /* if write didn't set errno, assume problem is no disk space */
> if (errno == 0)
> ***************
> *** 5837,5839 ****
> --- 5870,5940 ----
> errmsg("could not remove file \"%s\": %m",
> BACKUP_LABEL_FILE)));
> }
> +
> +
> + /* XLog gather-write staffs */
> +
> + static void
> + XLogPageReset(XLogPages *pages)
> + {
> + memset(pages, 0, sizeof(*pages));
> + }
> +
> + static void
> + XLogPageWrite(XLogPages *pages, int index)
> + {
> + char *page = XLogCtl->pages + index * BLCKSZ;
> + int size = BLCKSZ;
> + int offset = (LogwrtResult.Write.xrecoff - BLCKSZ) % XLogSegSize;
> +
> + if (pages->head + pages->size == page
> + && pages->offset + pages->size == offset)
> + { /* Pages are continuous. Append new page. */
> + pages->size += size;
> + }
> + else
> + { /* Pages are not continuous. Flush and clear. */
> + XLogPageFlush(pages, PrevBufIdx(index));
> + pages->head = page;
> + pages->size = size;
> + pages->offset = offset;
> + }
> + }
> +
> + static void
> + XLogPageFlush(XLogPages *pages, int index)
> + {
> + if (!pages->head)
> + { /* No needs to write pages. */
> + XLogCtl->Write.curridx = index;
> + return;
> + }
> +
> + /* Need to seek in the file? */
> + if (openLogOff != pages->offset)
> + {
> + openLogOff = pages->offset;
> + if (lseek(openLogFile, (off_t) openLogOff, SEEK_SET) < 0)
> + ereport(PANIC,
> + (errcode_for_file_access(),
> + errmsg("could not seek in log file %u, segment %u to offset %u: %m",
> + openLogId, openLogSeg, openLogOff)));
> + }
> +
> + /* OK to write the page */
> + errno = 0;
> + if (write(openLogFile, pages->head, pages->size) != pages->size)
> + {
> + /* if write didn't set errno, assume problem is no disk space */
> + if (errno == 0)
> + errno = ENOSPC;
> + ereport(PANIC,
> + (errcode_for_file_access(),
> + errmsg("could not write to log file %u, segment %u at offset %u: %m",
> + openLogId, openLogSeg, openLogOff)));
> + }
> +
> + openLogOff += pages->size;
> + XLogCtl->Write.curridx = index;
> + XLogPageReset(pages);
> + }

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