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From Lily Wei <lily...@yahoo.com>
Subject Re: Derby in-memory back end - where to go next?
Date Wed, 09 Sep 2009 19:45:50 GMT
Hi Rick:
     Thank you so much for sharing the information with the group.
>* It would be great to be able to bound the growth of the in-memory db
Is there a trend for need of in-memory db on JAVA world? Is it mainly for applications, i.e.
ERP, CRM, SRM? What kind of solution JAVA can provide for smart device like iPhone, RIMM or
Plam? i.e. Will JAVA play well with WindowMobile or Arnoid? 
Thank you for shed the lights for us in advance,

From: Rick Hillegas <Richard.Hillegas@Sun.COM>
To: Derby Discussion <derby-user@db.apache.org>
Sent: Wednesday, September 9, 2009 11:13:05 AM
Subject: Re: Derby in-memory back end - where to go next?

Hi Kristian,

Here's another piece of feedback: Last night I gave an overview of Derby to the San Francisco
Java User's Group. A developer asked whether the growth of the in-memory database could be
bounded. He had a use case which we didn't explore in depth but which involved periodically
truncating the database. I asked him to bring his requirements to the Derby user list so that
we could feed them into your spec effort. Here are my takeaways:

* It would be great to be able to bound the growth of the in-memory db

* It would be great if the memory occupied by deleted records could be released


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
> If new features are added, these must be documented as well.
> * 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.
> * Automatic deletion on database shutdown (or when last connection disconnects)
> * "Anonymous in-memory databases"
> A database which only the connection creating it can access, and when the connection
goes away the database goes away.
> * 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.
> * 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?
> * No derby.log
> Include a class in Derby that will discard everything written to derby.log.
> Thank you for your feedback,

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