pg_next_dst_boundary optimization

While profiling loading a table with timestamp columns with COPY, I
spotted that a lot of time is spent in pg_next_dst_boundary. It scans a
sorted array of time segments to find the one that the given timestamp
falls within. That's slow when the array is big; GB timezone for example
has > 200 segments.

Attached is a patch to use binary search instead of linear search. On my
laptop, it reduces the time required to load million rows to this test
table:

CREATE TABLE timestamptable (
id int,
ts1 timestamp,
ts2 timestamp,
ts3 timestamp,
ts4 timestamp
);

from ~16.4s to ~11.9s.

It would be nice to slip this into 8.3...

--
Heikki Linnakangas
EnterpriseDB http://www.enterprisedb.com