db-derby-user mailing list archives

Site index · List index
Message view « Date » · « Thread »
Top « Date » · « Thread »
From "Jason Boehle" <jboe...@actuate.com>
Subject question about Derby property and hash joins
Date Thu, 01 Feb 2007 16:48:51 GMT
The 10.2 tuning document says:

"The hash table for a hash join is held in memory and if it gets big
enough, it will spill to
the disk. The optimizer makes a very rough estimate of the amount of
memory required
to make the hash table. If it estimates that the amount of memory
required would exceed
the system-wide limit of memory use for a table, the optimizer chooses a
nested loop join
instead.
"If memory use is not a problem for your environment, set this property
to a high number;
allowing the optimizer the maximum flexibility in considering a join
strategy queries
involving large queries leads to better performance. It can also be set
to smaller values
for more limited environments."

What Derby property is it talking about, that represents the system-wide
limit of memory use for a table?

Thanks,
Jason Boehle
jboehle@actuate.com

Mime
View raw message