Affects Version/s: None
Fix Version/s: None
Because of reasons similar to IMAP-371 the performance of James Imap suffers when there are many clients.
The core issue is that the Mailbox/Message Mappers methods implementations can be potentially quite expensive, yet in many cases their result is "constant" for the input arguments, when the underlying data does not change. This makes them a good candidate for caching.
Another issue is that some of the methods are possibly needlessly called mutiple times inside a single request, and this is in focus of IMAP-371.
The cache can be implemented for example using Decorator pattern on top of the existing Mailbox/Message Mappers.
In the first step caching may involve MailboxMapper.findMailboxByPath, next steps may be some simple yet potentially expensive aspects of MessageMapper like countMessagesInMailbox(), countUnseenMessagesInMailbox(), getLastUid(), getHighestModSeq()
Because we have notifications that are fired when something happens to Mailboxes and Messages, it should be quite easy to invalidate stale cache entries. The invalidation can be registered as a global listener the AbstractDelegatingMailboxListener.
So: the general caching Mailbox/Message Mappers implementation would be abstract, and there needs to be a concrete implementation too.
For concrete implementation it would be nice to use something like guava Cache built with CacheBuilder with some nice options like proper TTL, size etc. The guestion is whether guava is license-compatible with James.
What do you think about it?