Re: [HACKERS] data on devel code perf dip

On Fri, 2005-08-12 at 14:53 -0400, Bruce Momjian wrote:
> 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.
So I'll use postgresql-20050728, I'll run with it to confirm it is
running similarly to my good run (42). If so, then I'll apply the patch
and see what happens....

This may take me a while just because I'm backed up with other
things ....

>
> ---------------------------------------------------------------------------
>
>
> >
> > 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)---------------------------
> > TIP 9: In versions below 8.0, the planner will ignore your desire to
> > choose an index scan if your joining column's datatypes do not
> > match
> >
>