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> If read or write fails. Position will left the same. This 

> situation is already tracked in File routines, but a little bit
> incorrectly.

> After small survey in Linux kernel code, I am not sure about
> it.  New patch set pos to unknown in the case of read/write
> fails. And do lseek again.

> Here is the full patch for this. This patch reduce amount of
> lseek call ten ti mes for update statement and twenty times for
> select statement. I tested joined up date and count(*) select
> for table with rows > 170000 and 10 indices.  I think this is
> worse of trying. Before lseek calls account for more than 5% o
> f time.  Now they are 0.89 and 0.15 respectevly.
>
> Due to only one file modification patch should be applied in
> src/backedn/stora ge/file/ dir.

-- Sincerely Yours,
Denis Perchine
This commit is contained in:
Bruce Momjian 2000-06-14 03:19:24 +00:00
parent 434adee656
commit a194574dde
1 changed files with 26 additions and 5 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

31
src/backend/storage/file/fd.c
View File

@ -7,7 +7,7 @@
* Portions Copyright (c) 1994, Regents of the University of California
*
* IDENTIFICATION
* $Header: /cvsroot/pgsql/src/backend/storage/file/fd.c,v 1.59 2000/06/02 15:57:24 momjian Exp $
* $Header: /cvsroot/pgsql/src/backend/storage/file/fd.c,v 1.60 2000/06/14 03:19:24 momjian Exp $
*
* NOTES:
*
@ -95,6 +95,8 @@
#define FileIsNotOpen(file) (VfdCache[file].fd == VFD_CLOSED)
#define FileUnknownPos (-1)
typedef struct vfd
{
signed short fd; /* current FD, or VFD_CLOSED if none */
@ -790,6 +792,8 @@ FileRead(File file, char *buffer, int amount)
returnCode = read(VfdCache[file].fd, buffer, amount);
if (returnCode > 0)
VfdCache[file].seekPos += returnCode;
else
VfdCache[file].seekPos = FileUnknownPos;
return returnCode;
}
@ -806,11 +810,12 @@ FileWrite(File file, char *buffer, int amount)
FileAccess(file);
returnCode = write(VfdCache[file].fd, buffer, amount);
if (returnCode > 0)
if (returnCode > 0) {
VfdCache[file].seekPos += returnCode;
/* mark the file as needing fsync */
VfdCache[file].fdstate |= FD_DIRTY;
} else
VfdCache[file].seekPos = FileUnknownPos;
return returnCode;
}
@ -840,10 +845,26 @@ FileSeek(File file, long offset, int whence)
default:
elog(ERROR, "FileSeek: invalid whence: %d", whence);
break;
}
}
else
} else
switch (whence) {
case SEEK_SET:
if (offset < 0)
elog(ERROR, "FileSeek: invalid offset: %ld", offset);
if (VfdCache[file].seekPos != offset)
VfdCache[file].seekPos = lseek(VfdCache[file].fd, offset, whence);
break;
case SEEK_CUR:
if ((offset != 0) || (VfdCache[file].seekPos == FileUnknownPos));
VfdCache[file].seekPos = lseek(VfdCache[file].fd, offset, whence);
break;
case SEEK_END:
VfdCache[file].seekPos = lseek(VfdCache[file].fd, offset, whence);
break;
default:
elog(ERROR, "FileSeek: invalid whence: %d", whence);
break;
}
return VfdCache[file].seekPos;
}