Large results are very slow in pgcat

[JelteF]

Describe the bug
This only gets ~40TPS with the pgcat.minimal.config

pgbench -P 1  -r -h 127.0.0.1 -T 100 --select-only -p 6434 --protocol simple -c 1 -f <(echo "select '"$(seq 10000)"'")
pgbench (15.3, server 12.16 (Ubuntu 12.16-1.pgdg22.04+1))
starting vacuum...end.
progress: 1.0 s, 44.0 tps, lat 20.902 ms stddev 24.041, 0 failed
progress: 2.0 s, 37.0 tps, lat 27.298 ms stddev 24.211, 0 failed
progress: 3.0 s, 36.0 tps, lat 27.768 ms stddev 24.246, 0 failed
progress: 4.0 s, 39.0 tps, lat 25.638 ms stddev 24.298, 0 failed
progress: 5.0 s, 42.0 tps, lat 23.807 ms stddev 24.108, 0 failed
progress: 6.0 s, 28.0 tps, lat 35.717 ms stddev 21.997, 0 failed

But doing the same size query, while not returning something big is much faster:

pgbench -P 1  -r -h 127.0.0.1 -T 100 --select-only -p 6434 --protocol simple -c 1 -f <(echo "select 1 where '' != '"$(seq 10000)"'")
pgbench (15.3, server 12.16 (Ubuntu 12.16-1.pgdg22.04+1))
starting vacuum...end.
progress: 1.0 s, 1602.8 tps, lat 0.591 ms stddev 0.183, 0 failed
progress: 2.0 s, 1622.0 tps, lat 0.616 ms stddev 0.222, 0 failed
progress: 3.0 s, 1577.0 tps, lat 0.632 ms stddev 0.341, 0 failed
progress: 4.0 s, 1645.0 tps, lat 0.607 ms stddev 0.210, 0 failed

[levkk]

Isn't this expected? Why should we be able to return large result sets at the same speed as small ones?

[JelteF]

Some slowdown is expected, but not 40x slower. Up to 2x makes sense, since total traffic is multiplied by 2. PgBouncer and Odyssey don't have this huge slowdown.

[GEverding]

In production we see something similar. On queries that return either large rows or high row counts we see a 2-5x increase in latency over pgbouncer. Were still tweaking things but its been pretty consistent for us. We running docker pgcat:e1e4929d439313d987c352b4517a6d99627f3e9c

Showing 95th latencies for a query that return 200-500 rows. the left is pgbouncer and the right is pgcat

[levkk]

#616 (comment)

[drdrsh]

I verified that this was fixed in #749