Re: Optimizing pglz compressor

On Wed, Mar 6, 2013 at 10:53 AM, Andres Freund <andres(at)2ndquadrant(dot)com> wrote:
> On 2013-03-06 09:36:19 -0600, Merlin Moncure wrote:
>> On Wed, Mar 6, 2013 at 8:32 AM, Joachim Wieland <joe(at)mcknight(dot)de> wrote:
>> > On Tue, Mar 5, 2013 at 8:32 AM, Heikki Linnakangas
>> > <hlinnakangas(at)vmware(dot)com> wrote:
>> >> With these tweaks, I was able to make pglz-based delta encoding perform
>> >> roughly as well as Amit's patch.
>> >
>> > Out of curiosity, do we know how pglz compares with other algorithms, e.g. lz4 ?
>>
>> This has been a subject of much recent discussion. It compares very
>> poorly, but installing a new compressor tends to be problematic due to
>> patent concerns (something which I disagree with but it's there). All
>> that said, Heikki's proposed changes seem to be low risk and quite
>> fast.
>
> Imo the licensing part is by far the smaller one. The interesting part
> is making a compatible change to the way toast compression works that
> supports multiple compression schemes. Afaics nobody has done that work.
> After that the choice of to-be-integrated compression schemes needs to
> be discussed, sure.

That wasn't the conversation I remember. lz4 completely smokes pglz
(Heikki's changes notwithstanding) and is bsd licensed so AFAICS there
it no reason to support multiple compression technologies except for
migration purposes (and even if you did want to, a plausible way to do
that was identified).

...but that's a separate topic for another day. Heikki's proposal
seems like a win either way.

merlin