Re: [HACKERS] data on devel code perf dip - Mailing list pgsql-patches

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@candle.pha.pa.us> wrote:
> > >
> > > > Tom Lane wrote:
> > > > > Bruce Momjian <pgman@candle.pha.pa.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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--
  Bruce Momjian                        |  http://candle.pha.pa.us
  pgman@candle.pha.pa.us               |  (610) 359-1001
  +  If your life is a hard drive,     |  13 Roberts Road
  +  Christ can be your backup.        |  Newtown Square, Pennsylvania 19073