Prior to using etcd for node membership, the data director was created
during the cluster topology setup. Since that no longer exists, we
weren't actually creating the data directory before getting to
logStartup(). So this change ensure that the data directory exists.
There's no need to have two different translation readers, a single
reader can handle both partitions and fields at the same time, so we
can combine them. This may not actually change things much but was
a useful step in diagnosing a different problem with translate readers,
and I think it is a minor improvement so I'm preserving the patch
just in case.
If we are using replication, we can be a replica translate store for a
partition, which means we start a translate store reader to replicate
data for it. The translation logic does not admit *stopping* the
translate reader, only "resetting" it (stopping and immediately
restarting), so the translate reader just runs until it hits an error
and terminates, which it does even if perhaps it shouldn't. Oops.
Anyway, one potential failure mode is that if you hit timing just
right, you can end up trying to process translation *while* the
index is being closed, and the index can close its translation stores,
and make them all nil, right before we request a store and try to use
it. Another is a similar error, but during the initial startup of the
translate store readers. Either way, we want to error out of the
process cleanly if this happens.
This could also happen during initial creation, perhaps.
We're aborting translation sync on these errors, because otherwise
we'd continue accepting new keys, and then end up with our highest
known key being higher than some keys we missed; this way the next
restart will restart from the last key we have.
If we're the primary field translation node, we don't need to set up
translation replication; we only need that if we're *not*. So it
makes sense to test if !IsPrimaryFieldTranslationNode... except that
the test is to determine whether to return early. So it should not
be inverted.
