On 10/22/2014 04:14 PM, Teodor Sigaev wrote:
Just replace tag_hash in tidbitmap which uses hash_any to direct call of
hash_uint32, it saves ~5% of execution time.
An example:
# create extension btree_gin;
# select (v / 10)::int4 as i into t from generate_series(1, 5000000) as v;
# create index idx on t using gin (i);
# set enable_seqscan = off;
# explain analyze select * from t where i >= 0;
without patch: Execution time: 2427.692 ms
with patch: Execution time: 2319.376 ms
# explain analyze select * from t where i >= 100 and i<= 100;
without patch: Execution time: 524.441 ms
with patch: Execution time: 504.478 ms
Nice little speedup, for such a simple patch. On my laptop, "perf"
confirms that with the patch, about 5% of the CPU time is spent in
tag_blocknumber, and without it, about 8% is spent in tag_hash. That
gives a 3% speed up, which is in the same ballpark that you saw.
I'd suggest putting the new function in hashfn.c, where we already have
similar functions, string_hash, tag_hash, oid_hash and bitmap_hash. And
name it "blocknumber_hash", for consistency.
- Heikki
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