Re: PostgreSQL block size vs. LVM2 stripe width

Hi Manfred,

On 27 Mar, Manfred Koizar wrote:
> Mark,
>
> how often did you run your tests? Are the results reproduceable?

In this case, I've only done 1 per each combination. I've found the
results for this test to be reproduceable.

> On Fri, 26 Mar 2004 14:00:01 -0800 (PST), markw(at)osdl(dot)org wrote:
>> Linux-2.6.3, LVM2 Stripe Width
>> (going across)
>>PostgreSQL
>>BLCKSZ
>>(going down) 16 KB 32 KB 64 KB 128 KB 256 KB 512 KB
>>2 KB 2617 2656 2652 2664 2667 2642
>>4 KB 4393 4486 4577 4557 4511 4448
>>8 KB 4337 4423 4471 4576 4111 3642
>>16 KB 4412 4495 4532 4536 2985 2312
>>32 KB 3705 3784 3886 3925 2936 2362
>
> Unless someone can present at least an idea of a theory why a BLCKSZ of
> 8 KB is at a local minimum (1 or 2% below the neighbouring values) for
> stripe widths up to 64 KB I'm not sure whether we can trust these
> numbers.
>
> Before I hit the send button, I did a quick check of the link you
> provided. The links in the table contain the following test numbers:
>
> 16 KB 32 KB 64 KB 128 KB 256 KB 512 KB
> 2 KB 72 71 70 69 66 65
> 4 KB 64 63 62 61 60 58
> 8 KB 54 53 52 51 50 49
> 16 KB 79 78 77 76 75 74
> 32 KB 86 85 84 83 82 80
>
> Does this mean that you first ran all test with 8 KB, then with 4, 2, 16
> and 32 KB BLCKSZ? If so, I suspect that you are measuring the effects
> of something different.

Yes, that's correct, but why do you suspect that?

Mark