• Oran Agra's avatar
    if diskless repl child is killed, make sure to reap the pid (#7742) · 573246f7
    Oran Agra authored
    Starting redis 6.0 and the changes we made to the diskless master to be
    suitable for TLS, I made the master avoid reaping (wait3) the pid of the
    child until we know all replicas are done reading their rdb.
    
    I did that in order to avoid a state where the rdb_child_pid is -1 but
    we don't yet want to start another fork (still busy serving that data to
    replicas).
    
    It turns out that the solution used so far was problematic in case the
    fork child was being killed (e.g. by the kernel OOM killer), in that
    case there's a chance that we currently disabled the read event on the
    rdb pipe, since we're waiting for a replica to become writable again.
    and in that scenario the master would have never realized the child
    exited, and the replica will remain hung too.
    Note that there's no mechanism to detect a hung replica while it's in
    rdb transfer state.
    
    The solution here is to add another pipe which is used by the parent to
    tell the child it is safe to exit. this mean that when the child exits,
    for whatever reason, it is safe to reap it.
    
    Besides that, i'm re-introducing an adjustment to REPLCONF ACK which was
    part of #6271 (Accelerate diskless master connections) but was dropped
    when that PR was rebased after the TLS fork/pipe changes (5a477946).
    Now that RdbPipeCleanup no longer calls checkChildrenDone, and the ACK
    has chance to detect that the child exited, it should be the one to call
    it so that we don't have to wait for cron (server.hz) to do that.
    573246f7
replication.c 136 KB