Re: [HACKERS] data on devel code perf dip

Mary Edie Meredith wrote:
> 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.

Right, or use patch -R to reverse out the changes and revert to a
version with O_DIRECT.
>
> 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?

The patch adds O_DIRECT (which is not being used given your configure
paramters), and grouped WAL writes.

---------------------------------------------------------------------------

>
> 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);
> > + }
>
>
> ---------------------------(end of broadcast)---------------------------
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--
Bruce Momjian | http://candle.pha.pa.us
pgman(at)candle(dot)pha(dot)pa(dot)us | (610) 359-1001
+ If your life is a hard drive, | 13 Roberts Road
+ Christ can be your backup. | Newtown Square, Pennsylvania 19073