On 2015/08/30 13:06, David Rowley wrote:
It's likely not worth changing if there's cases when it'll be slower, but curiosity got the better of me and I wondered how extreme a case it would take to actually see a slowdown, and per my benchmark results the first used column would have to be about attnum 500.
I used the attached to benchmark. has_system_columns is the current method, has_system_columns2 has my changes. Lines are prefixed by the position where the first (and only) attnum appears in the bitmap set.
1 has_system_columns complete in 1.196000 1 has_system_columns2 complete in 0.170000 2 has_system_columns complete in 1.198000 2 has_system_columns2 complete in 0.167000 4 has_system_columns complete in 1.197000 4 has_system_columns2 complete in 0.170000 8 has_system_columns complete in 1.206000 8 has_system_columns2 complete in 0.203000 16 has_system_columns complete in 1.202000 16 has_system_columns2 complete in 0.237000 32 has_system_columns complete in 1.206000 32 has_system_columns2 complete in 0.232000 64 has_system_columns complete in 1.207000 64 has_system_columns2 complete in 0.268000 128 has_system_columns complete in 1.205000 128 has_system_columns2 complete in 0.368000 256 has_system_columns complete in 1.203000 256 has_system_columns2 complete in 0.780000 512 has_system_columns complete in 1.202000 512 has_system_columns2 complete in 1.302000 1024 has_system_columns complete in 1.199000 1024 has_system_columns2 complete in 3.539000
So, for what it's worth, could be 6 times faster for an "average" sized table, but hey, we're talking nanoseconds anyway...
That's interesting. But ISTM that that needs more discussion, so I'd like to leave the method as-is at least for now.
Thanks for the experiment! Best regards, Etsuro Fujita -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
