Lu, Chris (NIH/NLM/LHC) [C] wrote:
Dear Sir:
I run into Derby last week and found it is very nice and easy to use.
Especially with embedded mode makes it easy for software need to be
distributed. However there are two features that I can’t found in Derby:
1). Multiple users (connections)
Multiple connections are only provided for embedded Derby Server (not
the pure embedded mode, org.apache.derby.EmbeddedDriver). Please
correct me if I am wrong.
2). Read-only
Derby provide a way for running on read-only media. However, does not
provide a flag to set the database to
read-only. In our application, we store all data in the database and
don’t expect/want the end users to modify it after we distribute the
software.
Currently, we are using Hyper-Sonic SQL database. HSqlDb is also
developed in 100% Java and don’t provide multiple connection for
embedded mode with R-W mode. However, multiple connections are allowed
when the flag of “read-only” is set to “true” in the embedded mode.
Very nice and useful feature.
Just wondering if Derby plan to provide the same features in the near
future. Thank you very much and have a nice day!
n Chris, Ph.D.
n Sr. Systems Architect
n Lockheed Martin/MSD/NLM/NIH
Hi Chris -
Regarding 1: I've talked to many people familiar with Client Server
databases who read that
'embedded Derby can only be accessed from within a single JVM' and take
this as meaning it is single user. This is not true. You can establish
as many connections as you wish from within the same Java program/JVM
environment. It is multi-threaded and locking prevents connections from
stepping on each other. Please see my attempt to address this confusion
in the section " Is embedded Derby a multiuser database?" at:
http://www.ibm.com/developerworks/db2/library/techarticle/dm-0408bradbury/#cs_multi
<http://db.apache.org/derby/derby_downloads.html>
Regarding 2: The easiest way would be to place the database in a
jarfile. Jarfiles are read-only even when deployed to read-write
media. Accessing databases in a jar require use of special connection URL.
Another way to implement read only is to enable auththentication and
only give the users the access information to the read-only account(s).
This works when the database is implemented in any architecture. You
will want to define the required properties as database properties in
the same manner as described in the section "What are the steps needed
to implement user authentication and authorization " at:
http://www.ibm.com/developerworks/db2/library/techarticle/dm-0408bradbury/#cs_authenticate
Granted this is not as easy as flipping a switch or jaring up a DB
but eliminates the possibility that someone unjars the database or
unflips the switch.
Hope this helps
