I wrote:
I'd be cool with making it impossible to put an index on an NFS
volume prior to version 4.
Elaborating and clarifying...
IndexReader attempts to establish a read lock on the relevant
segments_N file. It doesn't bother to see whether the locking
attempt succeeds, though.
IndexFileDeleter, before deleting any files, always touches a test
file, attempts to lock it, and verifies that the lock succeeds. If
the locking test fails, it throws an exception rather than proceed.
In addition, the locking test is run at index creation time, so that
the user knows as soon as possible that their index is in a
problematic location.
I think the only way this would fail under NFS is if the client
machine with the reader is using NFS version 3, while the machine
with the writer is using version 4. But before this issue arose I
didn't have that much experience with the intricacies of NFS, so I
could be off-base.
This does bring back the permissions issue with IndexReader. A
search app may not have permission to establish a read lock on a file
within the index directory, and in that case, an IndexFileDeleter
could delete files out from under it.
Marvin Humphrey
Rectangular Research
http://www.rectangular.com/
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