Re: pg_fallocate

On Thu, Oct 31, 2013 at 01:16:44PM +0000, Mitsumasa KONDO wrote:
> --- a/src/backend/storage/file/fd.c
> +++ b/src/backend/storage/file/fd.c
> @@ -383,6 +383,21 @@ pg_flush_data(int fd, off_t offset, off_t amount)
>      return 0;
>  }
>  
> +/*
> + * pg_fallocate --- advise OS that the data pre-allocate continus file segments
> + * in physical disk.
> + *
> + * Not all platforms have fallocate. Some platforms only have posix_fallocate,
> + * but it ped zero fill to get pre-allocate file segmnets. It is not good
> + * peformance when extend new segmnets, so we don't use posix_fallocate.
> + */
> +int
> +pg_fallocate(File file, int flags, off_t offset, off_t nbytes)
> +{
> +#if defined(HAVE_FALLOCATE)
> +    return fallocate(VfdCache[file].fd, flags, offset, nbytes);
> +#endif
> +}

You should set errno to ENOSYS and return -1 if HAVE_FALLOCATE isn't
defined.

> --- a/src/backend/storage/smgr/md.c
> +++ b/src/backend/storage/smgr/md.c
> @@ -24,6 +24,7 @@
>  #include <unistd.h>
>  #include <fcntl.h>
>  #include <sys/file.h>
> +#include <linux/falloc.h>

This would have to be wrapped in #ifdef HAVE_FALLOCATE or
HAVE_LINUX_FALLOC_H; if you want to create a wrapper around fallocate() you
should add PG defines for the flags, too.  Otherwise it's probably easier to
just call fallocate() directly inside an #ifdef block as you did in xlog.c.

> @@ -510,6 +511,10 @@ mdextend(SMgrRelation reln, ForkNumber forknum, BlockNumber blocknum,
>       * if bufmgr.c had to dump another buffer of the same file to make room
>       * for the new page's buffer.
>       */
> +
> +    if(forknum == 1)
> +        pg_fallocate(v->mdfd_vfd, FALLOC_FL_KEEP_SIZE, 0, RELSEG_SIZE);
> +

Return value should be checked; if it's -1 and errno is something else than
ENOSYS or EOPNOTSUPP the disk space allocation failed and you must return an
error.

/ Oskari