[389-users] Re: CPU Scalability / Scaling

On 8/14/2020 9:04 AM, Ben Spencer wrote:
> After a little investigation I didn't find any recent information on
> how well / linearly 389 scales from a CPU perspective. I also realize
> this is a more complicated topic with many factors which actually play
> into it.
>
> Throwing the basic question out there: Does 389 scale fairly
> linearly as the number of CPUs are increased? Is there a point where
> it drops off?

Cached reads (cached anywhere : filesystem cache, db page pool, entry
cache) should scale quite well, at least to 4/6/8 CPU. I'm not sure
about today's 8+ CPU systems but would assume probably not great scaling
beyond 8 until proven otherwise.

Writes are going to be heavily serialized, assume no CPU scaling. Fast
I/O is what you need for write throughput.

> Where am I going with this?
> We are faced with either adding more CPUs to the existing servers or
> adding more instances or a combination of the two. The current servers
> have 10 CPU with the entire database fitting in RAM but, there is a
> regular flow of writes. Sometimes somewhat heavy thanks to batch
> updates. Gut feeling tells me to have more servers than a few huge
> servers largely because of the writes/updates and lock contention.
> Needing to balance the server sprawl as well.

I'd look at whether I/O throughput (Write IOPS particularly) can be
upgraded as a first step. Then perhaps look at system design to see if
the batch updates can be throttled/trickled to reduce the cross-traffic
interference. Usually the write load is the limiting factor scaling
because it has to be replayed on every server regardless of its read
workload.

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