On Tue, Dec 21, 2010 at 6:24 PM, Robert Haas <robertmh...@gmail.com> wrote: > On Mon, Dec 20, 2010 at 1:10 PM, Noah Misch <n...@leadboat.com> wrote: >> When the caller knows the smaller string length, memcmp and strncmp are >> functionally equivalent. Since memcmp need not watch each byte for a NULL >> terminator, it often compares a CPU word at a time for better performance. >> The >> attached patch changes use of strncmp to memcmp where we have the length of >> the >> shorter string. I was most interested in the varlena.c instances, but I >> tried >> to find all applicable call sites. To benchmark it, I used the attached >> "bench-texteq.sql". This patch improved my 5-run average timing of the >> SELECT >> from 65.8s to 56.9s, a 13% improvement. I can't think of a case where the >> change should be pessimal. > > This is a good idea. I will check this over and commit it.
A little benchmarking reveals that on my system (MacOS X 10.6.5) it appears that strncmp() is faster for a 4 character string, but memcmp() is faster for a 5+ character string. So I think most of these are pretty clear wins, but I have reverted the changes to src/backend/tsearch because I'm not entirely confident that lexemes and affixes will be long enough on average for this to be a win there. Please feel free to resubmit that part with performance results showing that it works out to a win. Some of the ltree changes produced compiler warnings, so I omitted those also. Committed the rest. -- Robert Haas EnterpriseDB: http://www.enterprisedb.com The Enterprise PostgreSQL Company -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
