Thanks for starting this discussion, Kristian. My thoughts inline...
Kristian Waagan wrote:
Hello,
In Derby 10.5 an in-memory back end, or storage engine, was included.
It stores all the data in main memory, with the exception of
derby.log. If this is news to you, and you want a quick intro to it,
see [1] and [2].
I'm trying to gather some feedback on whether the current
implementation is found acceptable, or if there are additional
features people would like to see. I expect some wishes to emerge, and
I plan to record these on the wiki page [1]. The page can then be used
to guide further work in this area.
To start the discussion, I'll list some potential features and tasks.
Feel free to comment on any one of them either by replying to this
thread, or by adding your comments to [1]. It can be a +1 or -1 on the
feature itself, a suggestion for a new feature, or details on what a
feature should look like.
* Documentation
Must at least document the JDBC subsubprotocol, and also explain how
to delete in-memory databases.
If new features are added, these must be documented as well.
+1
* Deletion of in-memory databases
Currently the only ways to delete an in-memory database are to restart
the JVM or use a static method that isn't part of Derby's public API.
A proper mechanism for deletion should be added.
+1
* Automatic deletion on database shutdown (or when last connection
disconnects)
I can see that this would be useful for some people. I wouldn't make
this the default behavior, however. There are some operations like
changing persistent database-wide properties that don't take effect
until you bounce the database--and those operations would be disabled if
auto-delete were the default behavior.
* "Anonymous in-memory databases"
A database which only the connection creating it can access, and when
the connection goes away the database goes away.
This sounds like a refinement of the previous option and I can see that
this would be a useful security feature.
* Automatic persistence
The database could be persisted to disk automatically based on certain
criteria. The most obvious ones are perhaps on a fixed interval and on
JVM shutdown.
+1
* Monitoring
The most basic information is how many in-memory databases exist in
the current JVM, and how big they are. How should this information be
presented? Should it be available to anyone having a connection to the
current JVM?
+1
As Bernt says, JMX is attractive.
* No derby.log
Include a class in Derby that will discard everything written to
derby.log.
The current mechanism for redirecting the error log to a user defined
stream seems easy and flexible enough to me. But the user documentation
should point out that applications need to redirect the error log if
they really want to run without leaving any fingerprints.
Thanks!
-Rick
Thank you for your feedback,
