On Tue, Jul 9, 2024 at 12:39 AM John H <johnh...@gmail.com> wrote: > > > Out of curiosity, did you compare with standby_slot_names_from_syncrep set > > to off > > and standby_slot_names not empty? > > I didn't think 'standby_slot_names' would impact TPS as much since > it's not grabbing the SyncRepLock but here's a quick test. > Writer with 5 synchronous replicas, 10 pg_recvlogical clients and > pgbench all running from the same server. > > Command: pgbench -c 4 -j 4 -T 600 -U "ec2-user" -d postgres -r -P 5 > > Result with: standby_slot_names = > 'replica_1,replica_2,replica_3,replica_4,replica_5' > > latency average = 5.600 ms > latency stddev = 2.854 ms > initial connection time = 5.503 ms > tps = 714.148263 (without initial connection time) > > Result with: standby_slot_names_from_syncrep = 'true', > synchronous_standby_names = 'ANY 3 (A,B,C,D,E)' > > latency average = 5.740 ms > latency stddev = 2.543 ms > initial connection time = 4.093 ms > tps = 696.776249 (without initial connection time) > > Result with nothing set: > > latency average = 5.090 ms > latency stddev = 3.467 ms > initial connection time = 4.989 ms > tps = 785.665963 (without initial connection time) > > Again I think it's possible to improve the synchronous numbers if we > cache but I'll try that out in a bit. >
Okay, so the tests done till now conclude that we won't get the benefit by using 'standby_slot_names_from_syncrep'. Now, if we increase the number of standby's in both lists and still keep ANY 3 in synchronous_standby_names then the results may vary. We should try to find out if there is a performance benefit with the use of synchronous_standby_names in the normal configurations like the one you used in the above tests to prove the value of this patch. -- With Regards, Amit Kapila.
