From: Tino Wildenhain <tino@wildenhain.de>
To: Craig A. James <cjames@modgraph-usa.com>
Cc: pgsql-performance@postgresql.org
Subject: Re: Performance of count(*)
Date: Thu, 22 Mar 2007 18:27:32 +0100
Message-ID: <4602BC84.8030101@wildenhain.de> (raw)
In-Reply-To: <4602BB19.9050306@modgraph-usa.com>
References: <Pine.LNX.4.62.0703221149210.13747@wr-linux02>
<200703221208.19358.albert@sedifa.com>
<Pine.LNX.4.64.0703221323590.1503@ismoli.solenovo.jns>
<20070322141807.GE11402@mathom.us>
<46029DE3.9030505@modgraph-usa.com>
<4602A15B.7000908@wildenhain.de>
<4602BB19.9050306@modgraph-usa.com>
Craig A. James schrieb:
> Tino Wildenhain wrote:
>> Craig A. James schrieb:
>> ...
>>> In our case (for a variety of reasons, but this one is critical), we
>>> actually can't use Postgres indexing at all -- we wrote an entirely
>>> separate indexing system for our data...
>>
>> ...There is no need to store or
>> maintain this information along with postgres when you can store
>> and maintain it directly in postgres as well.
>
> Whether we store our data inside or outside Postgres misses the point
> (in fact, most of our data is stored IN Postgres). It's the code that
> actually performs the index operation that has to be external to Postgres.
>
>> On top of that, postgres has a very flexible and extensible index
>> system.
>
> You guys can correct me if I'm wrong, but the key feature that's missing
> from Postgres's flexible indexing is the ability to maintain state
> across queries. Something like this:
>
> select a, b, my_index_state() from foo where ...
> offset 100 limit 10 using my_index(prev_my_index_state);
>
Yes, you are wrong :-) The technique is called "CURSOR"
if you maintain persistent connection per session
(e.g. stand allone application or clever pooling webapplication)
If its a naive web application you just store your session
in tables where you can easily maintain the scroll state
as well.
Regards
Tino
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To: pgsql-performance@postgresql.org
Cc: tino@wildenhain.de, cjames@modgraph-usa.com
Subject: Re: Performance of count(*)
In-Reply-To: <4602BC84.8030101@wildenhain.de>
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