Re: Compression of full-page-writes

On Fri, Oct 11, 2013 at 10:36 PM, Andres Freund <andres(at)2ndquadrant(dot)com> wrote:
> On 2013-10-11 09:22:50 +0530, Amit Kapila wrote:
>> I think it will be difficult to prove by using any compression
>> algorithm, that it compresses in most of the scenario's.
>> In many cases it can so happen that the WAL will also not be reduced
>> and tps can also come down if the data is non-compressible, because
>> any compression algorithm will have to try to compress the data and it
>> will burn some cpu for that, which inturn will reduce tps.
>
> Then those concepts maybe aren't such a good idea after all. Storing
> lots of compressible data in an uncompressed fashion isn't an all that
> common usecase. I most certainly don't want postgres to optimize for
> blank padded data, especially if it can hurt other scenarios. Just not
> enough benefit.
> That said, I actually have relatively high hopes for compressing full
> page writes. There often enough is lot of repetitiveness between rows on
> the same page that it should be useful outside of such strange
> scenarios. But maybe pglz is just not a good fit for this, it really
> isn't a very good algorithm in this day and aage.

Do you think that if WAL reduction or performance with other
compression algorithm (for ex. snappy) is better, then chances of
getting the new compression algorithm in postresql will be more?
Wouldn't it be okay, if we have GUC to enable it and have pluggable
api for calling compression method, with this we can even include
other compression algorithm's if they proved to be good and reduce the
dependency of this patch on inclusion of new compression methods in
postgresql?

With Regards,
Amit Kapila.
EnterpriseDB: http://www.enterprisedb.com