Subject Re: [firebird-support] In memory sorting consumes alot of space
Author Ann Harrison
On Thu, May 16, 2013 at 12:35 PM, haris_p_sw <haris_p_sw@...> wrote:

> Why Firebird sorts datasets loading whole rows into memory when the plan
> is NATURAL? Couldn't it sort only primary keys for example? There might be
> something I 'm missing...
Firebird actually doesn't sort whole rows, it sorts only the rows requested
in the query - so select * is your enemy here as well. If it were to sort
carrying only the columns in the ORDER BY clause and the RDB$DB_KEY, it
would then have to make random reads for each row in the result set.
Random reads all over the database are even more expensive than the block
reads used to retrieve sorted subsets of the query.

Allocate as much memory as feasible for sorts and use a fast disk (or disk
equivalent) for temp space.

Good luck,


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