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

On 2014-09-11 13:04:43 -0400, Robert Haas wrote:
> On Thu, Sep 11, 2014 at 12:58 PM, Andres Freund <andres(at)2ndquadrant(dot)com> wrote:
> > On 2014-09-11 12:55:21 -0400, Robert Haas wrote:
> >> I advise supporting pglz only for the initial patch, and adding
> >> support for the others later if it seems worthwhile. The approach
> >> seems to work well enough with pglz that it's worth doing even if we
> >> never add the other algorithms.
> >
> > That approach is fine with me. Note though that I am pretty strongly
> > against adding support for more than one algorithm at the same time.
>
> What if one algorithm compresses better and the other algorithm uses
> less CPU time?

Then we make a choice for our users. A configuration option about an
aspect of postgres that darned view people will understand with for the
marginal differences between snappy and lz4 doesn't make sense.

> I don't see a compelling need for an option if we get a new algorithm
> that strictly dominates what we've already got in all parameters, and
> it may well be that, as respects pglz, that's achievable. But ISTM
> that it need not be true in general.

If you look at the results lz4 is pretty much there. Sure, there's
algorithms which have a much better compression - but the time overhead
is so large it just doesn't make sense for full page compression.

Greetings,

Andres Freund

--
Andres Freund http://www.2ndQuadrant.com/
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