I am using the managed ESENT PersistentDictionary class to get my C# application to store data on a network share. It all works great, with one caveat. When I try to access the database from multiple client computers (all running my app), I sometimes get an exception with the message "System path already used by another database instance".
From the documentation, I gather than ESENT supports concurrency, so this should not be a problem. What am I doing wrong?
Thank you.
There's a slight misunderstanding. ESENT supports multi-threaded concurrency, but not multi-process concurrency. esent.dll opens the file exclusively, so any other process will get ACCESS_DENIED (with the exception of read-only mode -- multiple processes can open a database in read-only mode).
In addition, the file-locking over SMB isn't quite as rigid as with local file system access, and the caching behaviour is also different. It's not recommended that you have a database on a remote SMB share, although you'll probably not have a problem with it in real life. (And some of that guidance was based on older versions of SMB. Newer versions might have changed the implementation details enough so that it works perfectly -- I guess I just don't know enough. :)
In order to have multi-machine access, you'll have to write your own server process to handle requests from other machines. Sorry.
-martin