Re: Speeding up JSON + TSQUERY + GIN

On 01.03.2017 18:04, Jeff Janes wrote:
> On Wed, Mar 1, 2017 at 6:02 AM, Sven R. Kunze <srkunze(at)mail(dot)de
> <mailto:srkunze(at)mail(dot)de>> wrote:
>
> On 28.02.2017 17:49, Jeff Janes wrote:
>> Oh. In my hands, it works very well. I get 70 seconds to do the
>> {age: 20} query from pure cold caches, versus 1.4 seconds from
>> cold caches which was followed by pg_prewarm('docs','prefetch').
>>
>> How much RAM do you have? Maybe you don't have enough to hold
>> the table in RAM. What kind of IO system? And what OS?
>
> On my test system:
>
> RAM: 4GB
> IO: SSD (random_page_cost = 1.0)
> OS: Ubuntu 16.04
>
>
>
> 4GB is not much RAM to be trying to pre-warm this amount of data
> into. Towards the end of the pg_prewarm, it is probably evicting data
> read in by the earlier part of it.
>
> What is shared_buffers?

942MB.

But I see where you are coming from. How come that these queries need a
Recheck Cond? I gather that this would require reading not only the
index data but also the table itself which could be huge, right?

Sven