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From "Jean T. Anderson" <...@bristowhill.com>
Subject Re: Is Derby and in memory database?
Date Wed, 10 Aug 2005 20:00:44 GMT
manju sherif wrote:
> Hi,
>  
> Is derby an in memory database ? We are looking at in memoery databases 
> for high reponse reads and inserts. How does Derby compare with HSQL as 
> an in memory database?

In-memory database support is on the Apache Derby To Do list at 
http://db.apache.org/derby/DerbyToDo.html ; however, I don't believe it 
is actively being worked on. The developers on this list can say for sure.

Dan Debrunner listed 2 key differences between hsql and derby in this 
post to derby-user@db.apache.org:

http://mail-archives.apache.org/mod_mbox/db-derby-user/200409.mbox/%3c41409451.6060506@debrunners.com%3e

An extract from his post is down below:

> These are two main differences I see from a quick look at the HSQL docs.
> 
> Memory Use
> 
> Derby is setup like a traditional database system where data is stored
> on disk and a subset of that data is cached in a buffer cache or pool.
> 
> HSQL by default uses MEMORY tables (for standard CREATE TABLE
> statements), this always stores the entire data in memory. Thus this is
> fast, but obviously consumes memory. It is useful to look a process
> sizes as well as absolute times when running benchmarks.
> http://hsqldb.sourceforge.net/doc/guide/ch01.html#N1021D
> 
> 
> Transaction Model
> 
> Derby provides a complete thread-safe multi-connection model supporting
> all four JDBC/SQL isolation levels. Row level locking is used to support
> these isolation models.
> 
> HSQL provides the single isolation level, READ_UNCOMMITTED, also known
> as dirty read, even for update transactions. Issues with this model are
> described in the HSQL documentation at:
> http://hsqldb.sourceforge.net/doc/guide/ch02.html#N104D5


I hope this helps.

regards,

-jean


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