Suresh Thalamati wrote:
I tried the following steps to create a simple readonly DB on file
system it seems to work fine for me.
1) shutdown the DB with no pending transaction (this step is same for
jars also), to avoid rollbacks during recovery on a readonly system.
2) disable(deny) write permission for all the files/directories
under databases directory for the user id. that is starting the
DB. 3) derby store seems to recognize that database is read only
if is it unable to create/modify files under database directory.
4) start each JVM that access the database with property
derby.storage.tempDirectory
(D"derby.storage.tempDirectory=c:/temp/x2") to specify different
temp directory for each instance , for the queries to create
temporary files in different directories.
My guess is , you are not disabling the write permissions correctly
for the database directory on the OS. Otherwise it would not be
able to
boot in the in the write mode at all, because it needs to crearte
lock files, and log files ..etc to do anything.
You're right.
My problem here is, as my own user, I'm setting the directory to
read-only, but under Windows that doesn't stop apps from writing to the
directory (whereas under Linux, for example, it would... unless that app
went and set the directory writeable somehow again.) But...
unfortunately, we want to support this scenario where one user creates
some data, then sets their own data into read-only so that others can
look at it. So I'll have to come up with some other workaround.
I think my workaround might need to be some kind of classloader trick.
If I load the database from the classpath, even if the actual data is on
the filesystem, Derby should still open in read-only mode. The trick is
going to be making a custom ClassLoader pointing to the parent directory
of the database, and then somehow getting Derby to use that classpath
instead of its normal one. I guess if I load Derby from that same
ClassLoader, then it should work. Maybe there is another way though.
I guess another really horrible way to do it would be to add every
filesystem root to the classpath. It would be a bit heavy-handed, but I
guess it would work as a last resort. :-)
Daniel
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Daniel Noll
NUIX Pty Ltd
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