This task is to re-think how should we do clean up of locally copied index files which are no longer in use.
- index writers, while creating index files, keep list of currently-being-written files
- this list is cleared when a new index writer comes into play
- index tracker opens new index (at new revision) via observation
- while being opened, we also track current dir listing of the local index files
- during opening new index, the tracker closes the old revision of index reader
- during this close, local files noted above during open are purged if ( they don't show up in remote view of the index && they aren't part of currently being written list by index writer)
This approach, at least in following timeline, would incur extra copying (and as a side-effect also open some index files directly off of remote input stream during CoWs):
- CoW1 creates [a, b]
- CoW2 starts and creates [c, d], removes [a, b] from remote
- CoR1 opens an index due to CoW1
- local-list-CoR1 = [a, b, c, d], remote-index-list=[a, b]
- CoW2 finishes
- CoW3 creates [e, f], removes [a,b] from remote
- CoR2 opens due to CoW2
- local-list-CoR2=[a,b,c,d,e,f], remote-index-list=[c,d]
- CoR1 closes
- deletes [c,d] as they aren't in its list of index files ([a,b]) AND aren't part of shared list ([e,f])
Disclaimer: the timeline might be off a bit (haven't written a test yet... but the basic point is that CoR could be working with a index file set and the new files might have come in twice after CoR - thus shared list doesn't have complete information of new files written in.
Chetan Mehrotra, can you please check the timeline above - I'd try to work on a test case in the mean time.