Re: PostgreSQL Read IOPS limit per connection

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On Wed, 9 Jan 2019 at 19:20, Merlin Moncure (via Accelo) <mmoncure(at)gmail(dot)com>
wrote:

> On Wed, Jan 9, 2019 at 3:52 PM Haroldo Kerry <hkerry(at)callix(dot)com(dot)br> wrote:
>
>> @Justin @Merlin @ Jeff,
>> Thanks so much for your time and insights, they improved our
>> understanding of the underpinnings of PostgreSQL and allowed us to deal the
>> issues we were facing.
>> Using parallel query on our PG 9.6 improved a lot the query performance -
>> it turns out that a lot of our real world queries could benefit of parallel
>> query, we saw about 4x improvements after turning it on, and now we see
>> much higher storage IOPS thanks to the multiple workers.
>> On our tests effective_io_concurrency did not show such a large effect as
>> the link you sent, I'll have a new look at it, maybe we are doing something
>> wrong or the fact that the SSDs are on the SAN and not local affects the
>> results.
>> On the process we also learned that changing the default Linux I/O
>> scheduler from CFQ to Deadline worked wonders for our Dell SC2020 SAN
>> Storage setup, we used to see latency peaks of 6,000 milliseconds on busy
>> periods (yes, 6 seconds), we now see 80 milliseconds, an almost 100 fold
>> improvement.
>>
>
> The links sent was using a contrived query to force a type of scan that
> benefits from that kind of query; it's a very situational benefit. It
> would be interesting if you couldn't reproduce using the same mechanic.
>
> merlin
>
>>