On Fri, Jul 26, 2024 at 5:11 PM Amit Kapila <amit.kapil...@gmail.com> wrote: > > On Fri, Jul 26, 2024 at 3:28 PM shveta malik <shveta.ma...@gmail.com> wrote: > > > > On Tue, Jul 23, 2024 at 10:35 AM Amit Kapila <amit.kapil...@gmail.com> > > wrote: > > > > > > 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. > > > > > > > I didn't fully understand the parameters mentioned above, specifically > > what 'latency stddev' and 'latency average' represent.. But shouldn't > > we see the benefit/value of this patch by having a setup where a > > particular standby is slow in sending the response back to primary > > (could be due to network lag or other reasons) and then measuring the > > latency in receiving changes on failover-enabled logical subscribers? > > We can perform this test with both of the below settings and say make > > D and E slow in sending responses: > > 1) synchronous_standby_names = 'ANY 3 (A,B,C,D,E)' > > 2) standby_slot_names = A_slot, B_slot, C_slot, D_slot, E_slot. > > > > Yes, I also expect the patch should perform better in such a scenario > but it is better to test it. Also, irrespective of that, we should > investigate why the reported case is slower for > synchronous_standby_names and see if we can improve it.
+1 > BTW, you for 2), I think you wanted to say synchronized_standby_slots, > not standby_slot_names. We have recently changed the GUC name. yes, sorry, synchronized_standby_slots it is. thanks Shveta
