Re: Searching a disk-backed Map

"Mike Schilling" <>
Tue, 18 Aug 2009 23:39:37 -0700
Stefan Ram wrote:

 This should be a common need. Yet I am not aware of anything
 like it in Java SE. What is the most common (pure Java)
 solution to it?

 I would like to have an implementation of java.util.Map,
 which is constructed with an int ?m? and a ?f?.

 It will use no more than ?m? bytes of memory, but ?swap? out
 (the least often used) entries to the file ?f?, when they do
 not fit into the given memory size anymore.

If you look at ,
you'll find a Java implementation of a persistent map a co-worker and
I wrote many years ago. I don't recall all of its features (and I'm
too lazy to set up a CVS client and pull down the source to look at
it), but basically

* You can create, delete, update, and retrieve keyed records
* The file is single-user but transactional -- none of the changes are
saved until you issue a commit.
* You can adjust the size of the cache. I think all changed records
are help in memory, but unchanged ones can come and go
* The index is a btree

If you ever used a Btree repository in the old Forte application
development system, it'll probably be clear that this code is a Java
port of the same underlying technology.

At the time I handed it off, it had a full set of unit tests, but one
of the most annoying things about working on NetBeans was that I could
never convince anyone else that unit tests were an essential part of
the source code, as opposed to something to hand off to QA in case
they felt like running them sometime. As a result, while the source
code eventually got checked into this repository, the tests have
apparently been lost.

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