Sezai YILMAZ <sezai.yilmaz@pro-g.com.tr> writes:
> I changed the three hash indexes to btree.
> The performance is increased about 2 times (in PostgreSQL 7.3.4 1905
> rows/s).
> Concurrent inserts now work.
Concurrent inserts should work with hash indexes in 7.4, though not 7.3.
The slowdown you report probably is due to the rewrite of hash indexing
to allow more concurrency --- the locking algorithm is more complex than
it used to be. I am surprised that the effect is so large though.
Could you make your test program available?
> Changed indexes are more suitable for hash type.
Are they? How many distinct values are there in those columns?
I suspect that your test may be stressing the case where only a few hash
buckets are used and each bucket chain gets to be very long.
regards, tom lane