zrepl/daemon/pruner
Christian Schwarz 69bfcb7bed daemon/active: implement watchdog to handle stuck replication / pruners
ActiveSide.do() can only run sequentially, i.e. we cannot run
replication and pruning in parallel. Why?

* go-streamrpc only allows one active request at a time
(this is bad design and should be fixed at some point)
* replication and pruning are implemented independently, but work on the
same resources (snapshots)

A: pruning might destroy a snapshot that is planned to be replicated
B: replication might replicate snapshots that should be pruned

We do not have any resource management / locking for A and B, but we
have a use case where users don't want their machine fill up with
snapshots if replication does not work.
That means we _have_ to run the pruners.

A further complication is that we cannot just cancel the replication
context after a timeout and move on to the pruner: it could be initial
replication and we don't know how long it will take.
(And we don't have resumable send & recv yet).

With the previous commits, we can implement the watchdog using context
cancellation.
Note that the 'MadeProgress()' calls can only be placed right before
non-error state transition. Otherwise, we could end up in a live-lock.
2018-10-19 17:23:00 +02:00
..
pruner_test.go daemon/pruner: fix exercise (don't call it test) 2018-09-05 21:47:44 -07:00
pruner.go daemon/active: implement watchdog to handle stuck replication / pruners 2018-10-19 17:23:00 +02:00
state_enumer.go use enumer generate tool for state strings 2018-10-12 22:10:49 +02:00