Re: pgsql: Add GUC to enable compression of full page images stored in WAL.

On Wed, Mar 11, 2015 at 11:18 PM, Andres Freund <andres@2ndquadrant.com> wrote:
> On 2015-03-11 06:54:16 +0000, Fujii Masao wrote:
>> Add GUC to enable compression of full page images stored in WAL.
>
> This triggers a couple warnings here (gcc 4.9 and 5):
>
> /home/andres/src/postgresql/src/backend/access/transam/xloginsert.c: In function 'XLogInsert':
> /home/andres/src/postgresql/src/backend/access/transam/xloginsert.c:670:5: warning: 'cbimg.hole_length' may be used
uninitializedin this function [-Wmaybe-uninitialized] 
>      memcpy(scratch, &cbimg,
>      ^
> /home/andres/src/postgresql/src/backend/access/transam/xloginsert.c:494:33: note: 'cbimg.hole_length' was declared
here
>    XLogRecordBlockCompressHeader cbimg;
>                                  ^
> /home/andres/src/postgresql/src/backend/access/transam/xloginsert.c:668:20: warning: 'hole_length' may be used
uninitializedin this function [-Wmaybe-uninitialized] 
>     if (hole_length != 0 && is_compressed)
>                     ^
> /home/andres/src/postgresql/src/backend/access/transam/xloginsert.c:497:10: note: 'hole_length' was declared here
>    uint16 hole_length;
>
> I've not checked whether they're spurious or not.

That's a little bit surprising, hole_offset is set and used only when
needs_backup == true, same with cbigm.hole_offset when (needs_backup
&& is_compressed && hole_offset != 0).
--
Michael