Re: [REVIEW] Re: Compression of full-page-writes

On Thu, Dec 18, 2014 at 7:31 PM, Rahila Syed <rahilasyed90@gmail.com> wrote:
>>Isn't it better to allocate the memory for compression_scratch in
>>InitXLogInsert()
>>like hdr_scratch?
>
> I think making compression_scratch a statically allocated global variable
> is the result of  following discussion earlier,
>
> http://www.postgresql.org/message-id/CA+TgmoazNBuwnLS4bpwyqgqteEznOAvy7KWdBm0A2-tBARn_aQ@mail.gmail.com
   /*    * Permanently allocate readBuf.  We do it this way, rather than just    * making a static array, for two
reasons:(1) no need to waste the    * storage in most instantiations of the backend; (2) a static char array    * isn't
guaranteedto have any particular alignment, whereas palloc()    * will provide MAXALIGN'd storage.    */
 

The above source code comment in XLogReaderAllocate() makes me think that
it's better to avoid using a static array. The point (1) seems less important in
this case because most processes need the buffer for WAL compression,
though.

Regards,

-- 
Fujii Masao