Java Doc for FileResourceManager.java in  » Database-JDBC-Connection-Pool » Apache-commons-transaction-1.2 » org » apache » commons » transaction » file » Java Source Code / Java DocumentationJava Source Code and Java Documentation

• Transactions performed with this class more or less comform to the widely accepted ACID properties
• Reading should be as fast as from the ordinary file system (at the cost of a bit slower commits)

• Number of simultaneously open resources is limited to the number of available file descriptors
• It does not scale a bit
• Pessimistic transaction and locking scheme
• Isolation level currently is restricted to read committed and repeated read (which is not that bad)

• On commit it might be necessay to copy files instead of rename/relink them. This may lead to time consuming, overly blocking commit phases and higher risk of corrupted files
• Prepare phase might be too permissive, no check for sufficient memory on store file system is possible

• Due to lack of synchronization on the transaction context level, every transaction may only be accessed by a single thread throughout its full life. This means it is forbidden for a thread that has not started a transaction to perform any operations inside this transaction. However, threads associated with different transactions can safely access these methods concurrently. Reasons for the lack of synchronization are improved performance and simplicity (of the code of this class).
• There is no dedicated class for a transaction. Having such a class would be better practice and make certain actions more intuitive.
• Resource identifiers need a reasonsable string representation obtainable by toString. More specifically, they will have to resolve to a valid file path that does note denote a directory. If it does, you might be able to create it, but not to read or write anything from resp. to it. Valid string representations of a resource idenfier are for example "file" "/root" or "hjfhdfhuhuhsdufhdsufhdsufhdfuhdfduhduhduhdu". Invalid are for example "/" or "/root/". Invalid on some file systems are for example "c:" or "file://huhu".
• As there are no active processes inside this RM and it shares its threads with the application, control over transactions is limited to points where the application calls the RM. In particular, this disables active termination of transactions upon timeout.
• There is no notion of a connection to this file manager. This means you can not connect from hosts other than local and you will get problems when plugging this store into a J2EE store using connectors.
• Methods should throw more specific exceptions

Caution:
The txId passed to many methods as an identifier for the transaction concerned will function as a key in a HashMap. Thus assure that equals and hashCode are both properly implemented and match each other.

Caution:
You will have to guarantee that no other process will access neither the store or the working dir concurrently to this FileResourceManager.

Special Caution:
Be very careful not to have two instances of FileResourceManager working in the same store and/or working dir.
version:
   $Id: FileResourceManager.java 509474 2007-02-20 09:04:22Z antoine $