Re: [HACKERS] Custom compression methods

On 3/19/19 10:59 AM, Chris Travers wrote:
>
>
> Not discussing whether any particular committer should pick this up but
> I want to discuss an important use case we have at Adjust for this sort
> of patch.
>
> The PostgreSQL compression strategy is something we find inadequate for
> at least one of our large deployments (a large debug log spanning
> 10PB+).  Our current solution is to set storage so that it does not
> compress and then run on ZFS to get compression speedups on spinning disks.
>
> But running PostgreSQL on ZFS has some annoying costs because we have
> copy-on-write on copy-on-write, and when you add file fragmentation... I
> would really like to be able to get away from having to do ZFS as an
> underlying filesystem.  While we have good write throughput, read
> throughput is not as good as I would like.
>
> An approach that would give us better row-level compression  would allow
> us to ditch the COW filesystem under PostgreSQL approach.
>
> So I think the benefits are actually quite high particularly for those
> dealing with volume/variety problems where things like JSONB might be a
> go-to solution.  Similarly I could totally see having systems which
> handle large amounts of specialized text having extensions for dealing
> with these.
>

Sure, I don't disagree - the proposed compression approach may be a big
win for some deployments further down the road, no doubt about it. But
as I said, it's unclear when we get there (or if the interesting stuff
will be in some sort of extension, which I don't oppose in principle).

>
>     But hey, I think there are committers working for postgrespro, who might
>     have the motivation to get this over the line. Of course, assuming that
>     there are no serious objections to having this functionality or how it's
>     implemented ... But I don't think that was the case.
>
>
> While I am not currently able to speak for questions of how it is
> implemented, I can say with very little doubt that we would almost
> certainly use this functionality if it were there and I could see plenty
> of other cases where this would be a very appropriate direction for some
> other projects as well.
>
Well, I guess the best thing you can do to move this patch forward is to
actually try that on your real-world use case, and report your results
and possibly do a review of the patch.

IIRC there was an extension [1] leveraging this custom compression
interface for better jsonb compression, so perhaps that would work for
you (not sure if it's up to date with the current patch, though).

[1]
https://www.postgresql.org/message-id/20171130182009.1b492eb2%40wp.localdomain

regards

--
Tomas Vondra                  http://www.2ndQuadrant.com
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