On Thu, Feb 13, 2014 at 10:20:46AM +0530, Amit Kapila wrote: > > Why not *only* prefix/suffix? > > To represent prefix/suffix match, we atleast need a way to tell > that the offset and len of matched bytes and then how much > is the length of unmatched bytes we have copied. > I agree that a simpler format could be devised if we just want to > do prefix-suffix match, but that would require much more test > during recovery to ensure everything is fine, advantage with LZ > format is that we don't need to bother about decoding, it will work > as without any much change in LZ decode routine.
Based on the numbers I think prefix/suffix-only needs to be explored. Consider if you just change one field of a row --- prefix/suffix would find all the matching parts. If you change the first and last fields, you get no compression at all, but your prefix/suffix test isn't going to get that either. As I understand it, the only place prefix/suffix with LZ compression is a win over prefix/suffix-only is when you change two middle fields, and there are common fields unchanged between them. If we are looking at 11% CPU overhead for that, it isn't worth it. -- Bruce Momjian <br...@momjian.us> http://momjian.us EnterpriseDB http://enterprisedb.com + Everyone has their own god. + -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
