On 7 January 2013 13:36, Greg Stark <st...@mit.edu> wrote: > On Mon, Jan 7, 2013 at 10:21 AM, John R Pierce <pie...@hogranch.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.
Good point, and a great reason to use this patch rather than LZ4 for 9.3 We could even have tuning parameters for toast compression, as long as we keep the on disk format identical. -- Simon Riggs http://www.2ndQuadrant.com/ PostgreSQL Development, 24x7 Support, Training & Services -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
