Re: Anyone for SSDs?

From: Josh Berkus <josh(at)agliodbs(dot)com>
To: Robert Haas <robertmhaas(at)gmail(dot)com>
Cc: Daniel Loureiro <loureirorg(at)gmail(dot)com>, Vaibhav Kaushal <vaibhavkaushal123(at)gmail(dot)com>, pgsql-hackers(at)postgresql(dot)org
Subject: Re: Anyone for SSDs?
Date: 2010-12-10 23:39:04
Message-ID: 4D02BA18.2080105@agliodbs.com
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>> Heck, even RAM isn't 1.0. I'm also involved with the Redis project,
>> which is an in-memory database. Even for a pure-RAM database, it turns
>> out that just using linked lists and 100% random access is slower than
>> accessing page images.
>
> That's a slightly different problem, though. Sequential vs. random
> access is about whether fetching pages n, n+1, n+2, ... is faster than
> skipping around, not whether accessing fewer pages is faster than
> more.

It's not though. Redis stores stuff as lists and sets, so it actually
does a lot of sequential access of data. Like if people are accessing
an ordered set, they're usually pulling the whole thing. It turns out
that *even in RAM* storing stuff in an ordered fashion on data "pages"
is more efficient than just using pointers.

--
-- Josh Berkus
PostgreSQL Experts Inc.
http://www.pgexperts.com

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