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Re: Anyone for SSDs?

From: Jeff Janes <jeff(dot)janes(at)gmail(dot)com>
To: Vaibhav Kaushal <vaibhavkaushal123(at)gmail(dot)com>
Cc: Josh Berkus <josh(at)agliodbs(dot)com>, pgsql-hackers(at)postgresql(dot)org
Subject: Re: Anyone for SSDs?
Date: 2010-12-11 19:09:07
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Lists: pgsql-hackers
On Fri, Dec 10, 2010 at 8:09 PM, Vaibhav Kaushal
<vaibhavkaushal123(at)gmail(dot)com> wrote:
> On Fri, 2010-12-10 at 18:07 -0800, Josh Berkus wrote:
>> On 12/10/10 5:06 PM, Daniel Loureiro wrote:
>> > An quicksort method in
>> > sequential disk its just awful to be thinking in a non SSD world, but
>> > its possible in an SSD.
>> So, code it.  Shouldn't be hard to write a demo comparison.  I don't
>> believe that SSDs make quicksort-on-disk feasible, but would be happy to
>> be proven wrong.
> I too do not believe it in normal case. However, considering the 'types'
> of SSDs, it may be feasible! Asking for 'the next page and getting it'
> has a time delay in the process. While on a regular HDD with spindles,
> the question is "where is that page located", with SSDs, the question
> disappears, because the access time is uniform in case of SSDs. Also,
> the access time is about 100 times fasterm which would change quite a
> few things about the whole process.

I don't understand what it is you are proposing.  Quicksort is usually
swap based, and so the records would need to be the same size.  Are
you proposing to do an in-memory sort of pointers, which reference
on-disk records?  Or an on-disk sort of pointers which reference
on-disk (but somewhere else) records?  If you are swapping pointers on
disk, you have to consider the write performance, not just the read

> I would like to do that (coding), but I do not have a SSD on my
> machine!

That doesn't mean you can't do the coding, it just means you can't
test the performance.
The barrier to get someone else to performance test it for you is a
lot lower than the
barrier to get someone else to write it for you and then performance
test it for you.
(But I can't test-drive it, as I don't have any computer which has
both an SSD and
a hard drive, just one or the other.  And the one with SSD would be
hard to compile
PG on.)

> :( Would it be impractical to try it for me? Again I do not
> know how to test PG :(

Yeah, I think it would be impractical.  If I thought it would likely
work, it would be different (at least, it might be if I had the right
But I think it would likely not work.



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