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Re: Improve compression speeds in pg_lzcompress.c

From: "ktm(at)rice(dot)edu" <ktm(at)rice(dot)edu>
To: Greg Stark <stark(at)mit(dot)edu>
Cc: John R Pierce <pierce(at)hogranch(dot)com>, pgsql-hackers(at)postgresql(dot)org
Subject: Re: Improve compression speeds in pg_lzcompress.c
Date: 2013-01-07 13:57:41
Message-ID: (view raw, whole thread or download thread mbox)
Lists: pgsql-hackers
On Mon, Jan 07, 2013 at 01:36:33PM +0000, Greg Stark wrote:
> On Mon, Jan 7, 2013 at 10:21 AM, John R Pierce <pierce(at)hogranch(dot)com> wrote:
> > On 1/7/2013 2:05 AM, Andres Freund wrote:
> >>
> >> I think there should be enough bits available in the toast pointer to
> >> indicate the type of compression. I seem to remember somebody even
> >> posting a patch to that effect?
> >> I agree that it's probably too late in the 9.3 cycle to start with this.
> >
> >
> > so an upgraded database would have old toasted values in the old compression
> > format, and new toasted values in the new format in an existing table?
> > that's kind of ugly.
> I haven't looked at the patch. It's not obvious to me from the
> description that the output isn't backwards compatible. The way the LZ
> toast compression works the output is self-describing. There are many
> different outputs that would decompress to the same thing and the
> compressing code can choose how hard to look for earlier matches and
> when to just copy bytes wholesale but the decompression will work
> regardless.

I think this comment refers to the lz4 option. I do agree that the patch
that was posted to improve the current compression speed should be able
to be implemented to allow the current results to be decompressed as well.


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Subject: Re: Improve compression speeds in pg_lzcompress.c
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