Re: unexpected psql "feature"

> Consider a throttled read-only load composed of 3 random selects,
> several rounds (so.sql) vs one (so2.sql):
>
> > pgbench -h server -T 100 -P 1 --rate 200 -c 2 -f so.sql -f so2.sql
> SQL script 1: so.sql
> - latency average = 1.878 ms
> SQL script 2: so2.sql
> - latency average = 1.089 ms
>
> There is 0.8 ms latency reduction, that is a 40% difference. Standard
> deviation is also significantly lower.

More fun with these two scripts, for those who focus on tps.

> pgbench -h server -M prepared -T 10 -P 1 -c 8 -f so.sql
...
latency average = 1.128 ms
latency stddev = 0.167 ms
tps = 7024.818252 (including connections establishing)

> pgbench -h server -T 10 -P 1 -c 8 -f so2.sql
# cannot do "-M prepared" on multiple commands... anyway:
...
latency average = 0.454 ms
latency stddev = 0.110 ms
tps = 17317.807554 (including connections establishing)

A mere 2.46 speedup for the read-only load.

The same with a "simple update" pgbench load, not compound & prepared:

latency average = 1.716 ms
latency stddev = 1.890 ms
tps = 4623.270608 (including connections establishing)

vs compound but not prepared:

latency average = 1.294 ms
latency stddev = 0.870 ms
tps = 6122.289249 (including connections establishing)

Ok, it is less impressive, just 30% better.

--
Fabien.