Re: ANALYZE sampling is too good

On 10/12/13 13:14, Mark Kirkwood wrote:
> On 10/12/13 12:14, Heikki Linnakangas wrote:
>>
>>
>> I took a stab at using posix_fadvise() in ANALYZE. It turned out to 
>> be very easy, patch attached. Your mileage may vary, but I'm seeing a 
>> nice gain from this on my laptop. Taking a 30000 page sample of a 
>> table with 717717 pages (ie. slightly larger than RAM), ANALYZE takes 
>> about 6 seconds without the patch, and less than a second with the 
>> patch, with effective_io_concurrency=10. If anyone with a good test 
>> data set loaded would like to test this and post some numbers, that 
>> would be great.
>>
>>
>
>
>
> I did a test run:
>
> pgbench scale 2000 (pgbench_accounts approx 25GB).
> postgres 9.4
>
> i7 3.5Ghz Cpu
> 16GB Ram
> 500 GB Velociraptor 10K
>
> (cold os and pg cache both runs)
> Without patch:  ANALYZE pgbench_accounts    90s
> With patch: ANALYZE pgbench_accounts  91s
>
> So I'm essentially seeing no difference :-(


Arrg - sorry forgot the important bits:

Ubuntu 13.10 (kernel 3.11.0-14)
filesystem is ext4