Re: ANALYZE sampling is too good

On 10/12/13 13:20, Mark Kirkwood wrote:
> 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
>
>
>

Doing the same test as above, but on a 80GB Intel 520 (ext4 filesystem 
mounted with discard):

(cold os and pg cache both runs)
Without patch:  ANALYZE pgbench_accounts  5s
With patch: ANALYZE pgbench_accounts  5s