Instead of writer pinning, we'll track the last transaction ID of each
write in the session. Then on each read we'll wait for the replica to
report that this transaction is available.
If it doesn't become available within a reasonable timeout, we'll
proceed anyway, and accept the possibility of a stale read.
The hope here is that most of the time, the replica is caught up in the
time between a write request and the following read request. If it's
not, we now have a little tolerance to wait for it, which hopefully
proves enough to stale reads are not encountered in normal use.
We also disable the writer affinity opt-out mechanism that we had
before, since we will no longer be using writer affinity at the load
balancer.
This adds an initial configuration for staging. Note that we are doing
this ahead of having the full infrastructure in all 3 DCs. So this
this will result in some cross-DC writes for now (e.g. we have a single cache in
IAD). We'll correct this as the infrastructure becomes available.
We'll also run jobs on every app server, until we split them out to
separate instances.
Kevin McConnell