34 lines
1.7 KiB
Markdown
34 lines
1.7 KiB
Markdown
Worked today on making incremental fsck's use of sqlite be safe with
|
|
multiple concurrent fsck processes.
|
|
|
|
The first problem was that having `fsck --incremental` running and starting a
|
|
new `fsck --incremental` caused it to crash. And with good reason, since
|
|
starting a new incremental fsck deletes the old database, the old process
|
|
was left writing to a datbase that had been deleted and recreated out from
|
|
underneath it. Fixed with some locking.
|
|
|
|
Next problem is harder. Sqlite doesn't support multiple concurrent writers
|
|
at all. One of them will fail to write. It's not even possible to have two
|
|
processes building up separate transactions at the same time. Before using
|
|
sqlite, incremental fsck could work perfectly well with multiple fsck
|
|
processes running concurrently. I'd like to keep that working.
|
|
|
|
My partial solution, so far, is to make git-annex buffer writes, and every
|
|
so often send them all to sqlite at once, in a transaction. So most of the
|
|
time, nothing is writing to the database. (And if it gets unlucky and
|
|
a write fails due to a collision with another writer, it can just wait and
|
|
retry the write later.) This lets multiple processes write to the database
|
|
successfully.
|
|
|
|
But, for the purposes of concurrent, incremental fsck, it's not ideal.
|
|
Each process doesn't immediately learn of files that another process has
|
|
checked. So they'll tend to do redundant work. Only way I can see to
|
|
improve this is to use some other mechanism for short-term IPC between the
|
|
fsck processes.
|
|
|
|
----
|
|
|
|
Also, I made `git annex fsck --from remote --incremental` use a different
|
|
database per remote. This is a real improvement over the sticky bits;
|
|
multiple incremental fscks can be in progress at once,
|
|
checking different remotes.
|