On Wed, Mar 6, 2013 at 8:53 AM, Andres Freund <and...@2ndquadrant.com>wrote:
> On 2013-03-06 09:36:19 -0600, Merlin Moncure wrote: > > On Wed, Mar 6, 2013 at 8:32 AM, Joachim Wieland <j...@mcknight.de> wrote: > > > On Tue, Mar 5, 2013 at 8:32 AM, Heikki Linnakangas > > > <hlinnakan...@vmware.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. > Another thing to consider would be some way of recording an exemplar value for each column which is used to seed whatever compression algorithm is used. I think there often a lot of redundancy that does not appear within any given value, but does appear when viewing all the values of a given column. Finding some way to take advantage of that could give a big improvement in compression ratio. Cheers, Jeff
