On Sat, Oct 25, 2014 at 12:38 PM, Andreas Karlsson <andr...@proxel.se> wrote:
> Hi, > > There was recently talk about if we should start using 128-bit integers > (where available) to speed up the aggregate functions over integers which > uses numeric for their internal state. So I hacked together a patch for > this to see what the performance gain would be. > > Previous thread: http://www.postgresql.org/message-id/20141017182500. > gf2...@alap3.anarazel.de > > What the patch does is switching from using numerics in the aggregate > state to int128 and then convert the type from the 128-bit integer in the > final function. > > The functions where we can make use of int128 states are: > > - sum(int8) > - avg(int8) > - var_*(int2) > - var_*(int4) > - stdev_*(int2) > - stdev_*(int4) > > The initial benchmark results look very promising. When summing 10 million > int8 I get a speedup of ~2.5x and similarly for var_samp() on 10 million > int4 I see a speed up of ~3.7x. To me this indicates that it is worth the > extra code. What do you say? Is this worth implementing? > > The current patch still requires work. I have not written the detection of > int128 support yet, and the patch needs code cleanup (for example: I used > an int16_ prefix on the added functions, suggestions for better names are > welcome). I also need to decide on what estimate to use for the size of > that state. > > The patch should work and pass make check on platforms where __int128_t is > supported. > > The simple benchmarks: > > CREATE TABLE test_int8 AS SELECT x::int8 FROM generate_series(1, 10000000) > x; > > Before: > > # SELECT sum(x) FROM test_int8; > sum > ---------------- > 50000005000000 > (1 row) > > Time: 2521.217 ms > > After: > > # SELECT sum(x) FROM test_int8; > sum > ---------------- > 50000005000000 > (1 row) > > Time: 1022.811 ms > > CREATE TABLE test_int4 AS SELECT x::int4 FROM generate_series(1, 10000000) > x; > > Before: > > # SELECT var_samp(x) FROM test_int4; > var_samp > -------------------- > 8333334166666.6667 > (1 row) > > Time: 3808.546 ms > > After: > > # SELECT var_samp(x) FROM test_int4; > var_samp > -------------------- > 8333334166666.6667 > (1 row) > > Time: 1033.243 ms > > Andreas > > > -- > Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) > To make changes to your subscription: > http://www.postgresql.org/mailpref/pgsql-hackers > > These are some nice improvements. As far as I'm aware int128 types are supported on every major compiler when compiling for 64bit platforms. Right?
