type cache cleanup improvements

Hi!

I'd like to suggest two independent patches to improve performance of type cache
cleanup. I found a case where type cache cleanup was a reason for low
performance. In short, customer makes 100 thousand temporary tables in one
transaction.

1 mapRelType.patch
It just adds a local map between relation and its type as it was suggested in
comment above TypeCacheRelCallback(). Unfortunately, using syscache here was
impossible because this call back could be called outside transaction and it
makes impossible catalog lookups.

2 hash_seq_init_with_hash_value.patch
TypeCacheTypCallback() loop over type hash to find entry with given hash
value. Here there are two problems: 1) there isn't interface to dynahash to
search entry with given hash value and 2) hash value calculation algorithm is
differ from system cache. But coming hashvalue is came from system cache. Patch
is addressed to both issues. It suggests hash_seq_init_with_hash_value() call
which inits hash sequential scan over the single bucket which could contain
entry with given hash value, and hash_seq_search() will iterate only over such
entries. Anf patch changes hash algorithm to match syscache. Actually, patch
makes small refactoring of dynahash, it makes common function hash_do_lookup()
which does initial lookup in hash.

Some artificial performance test is in attachment, command to test is 'time psql
< custom_types_and_array.sql', here I show only last rollback time and total
execution time:
1) master 92d2ab7554f92b841ea71bcc72eaa8ab11aae662
Time: 33353,288 ms (00:33,353)
psql < custom_types_and_array.sql 0,82s user 0,71s system 1% cpu 1:28,36 total

2) mapRelType.patch
Time: 7455,581 ms (00:07,456)
psql < custom_types_and_array.sql 1,39s user 1,19s system 6% cpu 41,220 total

3) hash_seq_init_with_hash_value.patch
Time: 24975,886 ms (00:24,976)
psql < custom_types_and_array.sql 1,33s user 1,25s system 3% cpu 1:19,77 total

4) both
Time: 89,446 ms
psql < custom_types_and_array.sql 0,72s user 0,52s system 10% cpu 12,137 total

--
Teodor Sigaev E-mail: teodor(at)sigaev(dot)ru
WWW: http://www.sigaev.ru/