From: "Jeff Janes" <jeff.ja...@gmail.com>
I thought that this was the point I was making, not the point I was
missing. You have the same hard drives you had before, but now due to a
software improvement you are cramming 5 times more stuff through them.
Yeah, you will get bigger latency spikes. Why wouldn't you? You are now
beating the snot out of your hard drives, whereas before you were not.
If you need 10,000 TPS, then you need to upgrade to 9.4. If you need it
with low maximum latency as well, then you probably need to get better IO
hardware as well (maybe not--maybe more tuning could help). With 9.3 you
didn't need better IO hardware, because you weren't capable of maxing out
what you already had. With 9.4 you can max it out, and this is a good
thing.
If you need 10,000 TPS but only 2000 TPS are completing under 9.3, then
what is happening to the other 8000 TPS? Whatever is happening to them, it
must be worse than a latency spike.
On the other hand, if you don't need 10,000 TPS, than measuring max
latency
at 10,000 TPS is the wrong thing to measure.
Thank you, I've probably got the point --- you mean the hard disk for WAL is
the bottleneck. But I still wonder a bit why the latency spike became so
bigger even with # of clients fewer than # of CPU cores. I suppose the
requests get processed more smoothly when the number of simultaneous
requests is small. Anyway, I want to believe the latency spike would become
significantly smaller on an SSD.
Regards
MauMau
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