Re: [HACKERS] TODO item - Mailing list pgsql-hackers

> BTW, I have worked a little bit on this item. The idea is pretty
> simple. Instead of doing a real fsync() in pg_fsync(), just marking it
> so that we remember to do fsync() at the commit time. Following
> patches illustrate the idea. An experience shows that it dramatically
> boosts the performance of copy. Unfortunately I see virtually no
> difference for TPC-B like small many concurrent transactions. Maybe we
> would need WAL for this. Comments?


Can you be more specific.  How does fsync work now vs. your proposed
change.  I did not see that here.  Sorry.


> 
> Index: access/transam/xact.c
> ===================================================================
> RCS file: /usr/local/cvsroot/pgsql/src/backend/access/transam/xact.c,v
> retrieving revision 1.60
> diff -c -r1.60 xact.c
> *** access/transam/xact.c    2000/01/29 16:58:29    1.60
> --- access/transam/xact.c    2000/02/06 06:12:58
> ***************
> *** 639,644 ****
> --- 639,646 ----
>       if (SharedBufferChanged)
>       {
>           FlushBufferPool();
> +         pg_fsync_pending();
> + 
>           if (leak)
>               ResetBufferPool();
>   
> ***************
> *** 653,658 ****
> --- 655,661 ----
>            */
>           leak = BufferPoolCheckLeak();
>           FlushBufferPool();
> +         pg_fsync_pending();
>       }
>   
>       if (leak)
> Index: storage/file/fd.c
> ===================================================================
> RCS file: /usr/local/cvsroot/pgsql/src/backend/storage/file/fd.c,v
> retrieving revision 1.52
> diff -c -r1.52 fd.c
> *** storage/file/fd.c    2000/01/26 05:56:55    1.52
> --- storage/file/fd.c    2000/02/06 06:13:01
> ***************
> *** 189,202 ****
>   static File fileNameOpenFile(FileName fileName, int fileFlags, int fileMode);
>   static char *filepath(char *filename);
>   static long pg_nofile(void);
>   
>   /*
>    * pg_fsync --- same as fsync except does nothing if -F switch was given
>    */
>   int
>   pg_fsync(int fd)
>   {
> !     return disableFsync ? 0 : fsync(fd);
>   }
>   
>   /*
> --- 189,238 ----
>   static File fileNameOpenFile(FileName fileName, int fileFlags, int fileMode);
>   static char *filepath(char *filename);
>   static long pg_nofile(void);
> + static void alloc_fsync_info(void);
>   
> + static char *fsync_request;
> + static int nfds;
> + 
>   /*
>    * pg_fsync --- same as fsync except does nothing if -F switch was given
>    */
>   int
>   pg_fsync(int fd)
> + {
> +     if (fsync_request == NULL)
> +       alloc_fsync_info();
> +     fsync_request[fd] = 1;
> +     return 0;
> + }
> + 
> + static void alloc_fsync_info(void)
> + {
> +   nfds = pg_nofile();
> +   fsync_request = malloc(nfds);
> +   if (fsync_request == NULL) {
> +     elog(ERROR, "alloc_fsync_info: cannot allocate memory");
> +     return;
> +   }
> + }
> + 
> + void
> + pg_fsync_pending(void)
>   {
> !   int i;
> ! 
> !   if (disableFsync)
> !     return;
> ! 
> !   if (fsync_request == NULL)
> !     alloc_fsync_info();
> ! 
> !   for (i=0;i<nfds;i++) {
> !     if (fsync_request[i]) {
> !       fsync(i);
> !       fsync_request[i] = 0;
> !     }
> !   }
>   }
>   
>   /*
> 


--  Bruce Momjian                        |  http://www.op.net/~candle pgman@candle.pha.pa.us               |  (610)
853-3000+  If your life is a hard drive,     |  830 Blythe Avenue +  Christ can be your backup.        |  Drexel Hill,
Pennsylvania19026