From: | "Merlin Moncure" <merlin(dot)moncure(at)rcsonline(dot)com> |
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To: | <alex(at)neteconomist(dot)com> |
Cc: | <pgsql-performance(at)postgresql(dot)org>, "Richard Huxton" <dev(at)archonet(dot)com> |
Subject: | Re: [SQL] OFFSET impact on Performance??? |
Date: | 2005-01-20 17:00:06 |
Message-ID: | 6EE64EF3AB31D5448D0007DD34EEB3412A75C6@Herge.rcsinc.local |
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Thread: | |
Lists: | pgsql-performance |
> I am also very interesting in this very question.. Is there any way to
> declare a persistant cursor that remains open between pg sessions?
> This would be better than a temp table because you would not have to
> do the initial select and insert into a fresh table and incur those IO
> costs, which are often very heavy, and the reason why one would want
> to use a cursor.
Yes, it's called a 'view' :-)
Everything you can do with cursors you can do with a view, including
selecting records in blocks in a reasonably efficient way. As long as
your # records fetched is not real small (> 10) and your query is not
super complex, you can slide your view just like a cursor with zero real
impact on performance.
If the query in question does not scale in time complexity with the
amount of data returned (there is a fix processing step which can't be
avoided), then it's materialized view time, such that they can be done
in PostgreSQL.
Now, cursors can be passed around in pl/pgsql functions which makes them
very useful in that context. However, for normal data processing via
queries, they have some limitations that makes them hard to use in a
general sense.
Merlin
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