Turns out sqlite does not like having its database deleted out from
underneath it. It might suffice to empty the table, but I would rather
start each fsck over with a new database, so I added a lock file, and
running incremental fscks use a shared lock.
This leaves one concurrency bug left; running two concurrent fsck --more
will lead to: "SQLite3 returned ErrorBusy while attempting to perform step."
and one or both will fail. This is a concurrent writers problem.
Database.Handle can now be given a CommitPolicy, making it easy to specify
transaction granularity.
Benchmarking the old git-annex incremental fsck that flips sticky bits
to the new that uses sqlite, running in a repo with 37000 annexed files,
both from cold cache:
old: 6m6.906s
new: 6m26.913s
This commit was sponsored by TasLUG.
Did not keep backwards compat for sticky bit records. An incremental fsck
that is already in progress will start over on upgrade to this version.
This is not yet ready for merging. The autobuilders need to have sqlite
installed.
Also, interrupting a fsck --incremental does not commit the database.
So, resuming with fsck --more restarts from beginning.
Memory: Constant during a fsck of tens of thousands of files.
(But, it does seem to buffer whole transation in memory, so
may really scale with number of files.)
CPU: ?
