Re: Why could different data in a table be processed with different performance?

Hi,
Assuming DB is quiescent.

And if you run?

select count(*) from articles where article_id between %s and %s

ie without reading json, is your buffers hit count increasing?
20 000 8K blocks *2 is 500MB , should be in RAM after the first run.

Fast:
read=710 I/O Timings: read=852.547 ==> 1.3 ms /IO
800 IO/s some memory, sequential reads or a good raid layout.

Slow:
read=5244 I/O Timings: read=24507.621 ==> 4.7 ms /IO
200 IO/s more HD reads? more seeks? slower HD zones ?

Maybe you can play with PG cache size.

On Sat, Sep 22, 2018 at 12:32 PM Vladimir Ryabtsev <greatvovan(at)gmail(dot)com>
wrote:

> > I think reindex will improve the heap access..and maybe the index access
> too. I don't see why it would be bloated without UPDATE/DELETE, but you
> could check to see if its size changes significantly after reindex.
> I tried REINDEX, and size of PK index changed from 2579 to 1548 MB.
> But test don't show any significant improvement from what it was. May be
> read speed for the "big" range became just slightly faster in average.
>
> Vlad
>
>