Ceph

Under some workloads, it is beneficial to avoid log-based recovery and use backfill instead. This lets I/O proceed on objects being backfilled, since it occurs in the background. This is implemented by setting the min/max pg log size to 1 and 2.

This has a side effect of eliminating our duplicate op detection. To make this configuration robust, we need to keep a separate structure to detect duplicate ops beyond the pg log entries.