this is useful for clone also to copy notes, operators, checklist
of the time when the backup was made (as opposed to current)
at this point, it's not clear why we need a archives table. it's
an optimization to not have to store icon for every backup.
Currently, the update/apptask/fullbackup/platformstart take a
global lock and cannot run in parallel. This causes situations
where when a user tries to trigger an apptask, it says "waiting for
backup to finish..." etc
The solution is to let them run in parallel. We need a lock at the
app level as app operations running in parallel would be bad (tm).
In addition, the update task needs a lock just for the update part.
We also need multi-process locks. Running tasks as processes is core
to our "kill" strategy.
Various inter process locks were explored:
* node's IPC mechanism with process.send(). But this only works for direct node.js
children. taskworker is run via sudo and the IPC does not work.
* File lock using O_EXCL. Basic ideas to create lock files. While file creation
can be done atomically, it becomes complicated to clean up lock files when
the tasks crash. We need a way to know what locks were held by the crashing task.
flock and friends are not built-into node.js
* sqlite/redis were options but introduce additional deps
* Settled on MySQL based locking. Initial plan was to have row locks
or table locks. Each row is a kind of lock. While implementing, it was found that
we need many types of locks (and not just update lock and app locks). For example,
we need locks for each task type, so that only one task type is active at a time.
* Instead of rows, we can just lock table and have a json blob in it. This hit a road
block that LOCK TABLE is per session and our db layer cannot handle this easily! i.e
when issing two db.query() it might use two different connections from the pool. We have to
expose the connection, release connection etc.
* Next idea was atomic blob update of the blob checking if old blob was same. This approach,
was finally refined into a version field.
Phew!
the exception is when sudo calls backupupload.js which already has timestamped
output because it uses node
an alternative idea is to maybe not use this flag at all and always parse the output.
this is a bit complicated since we have to look for a timestamp in a stream.
du error: Command failed: du -Dsb "/home/yellowtent/boxdata/mail" du: cannot access '/home/yellowtent/boxdata/mail/vmail/user@example.com/mail/dovecot-uidlist.lock': No such file or directory .
One idea was to compute this at cleanup time, but this has two problems:
* the UI won't reflect this value. can be good or bad
* the cleaner has no easy way to find out the "parent". I guess we should
change our data structure, if we want to go down this route...
the main motivation is that id can be used in REST API routes. previously,
the id was a path and this had a "/" in it. This made /api/v1/backups/:backupId
not work.
Girish Ramakrishnan