Greg Stark <st...@mit.edu> writes: > I'm still curious how it would compare to call strxfrm and sort the > resulting binary blobs.
In principle that should be a win; it's hard to believe that strxfrm would have gotten into the standards if it were not a win for sorting applications. > I don't think the sortsupport stuff actually > makes this any easier though. Since using it requires storing the > binary blob somewhere I think the support would have to be baked into > tuplesort (or hacked into the sortkey as an expr that was evaluated > earlier somehow). Well, obviously something has to be done, but I think it might be possible to express this as another sortsupport API function rather than doing anything as ugly as hardwiring strxfrm into the callers. However, it occurred to me that we could pretty easily jury-rig something that would give us an idea about the actual benefit available here. To wit: make a C function that wraps strxfrm, basically strxfrm(text) returns bytea. Then compare the performance of ORDER BY text_col to ORDER BY strxfrm(text_col). (You would need to have either both or neither of text and bytea using the sortsupport code paths for this to be a fair comparison.) One other thing I've always wondered about in this connection is the general performance of sorting toasted datums. Is it better to detoast them in every comparison, or pre-detoast to save comparison cycles at the cost of having to push much more data around? I didn't see any discussion of this point in Robert's benchmarks, but I don't think we should go very far towards enabling sortsupport for text until we understand the issue and know whether we need to add more infrastructure for it. If you cross your eyes a little bit, this is very much like the strxfrm question... regards, tom lane -- Sent via pgsql-hackers mailing list (firstname.lastname@example.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers