db: fix WAL replay in read-only mode

Question

The addition of memTable.logSeqNum broke WAL replay in read-only mode because we were initializing memTable.logSeqNum too early and setting it to the visible sequence number rather than the first sequence number in the WAL being replayed. This would result in an error during Open that looked like:

   pebble: batch seqnum 2 is less than memtable creation seqnum 3

该提问来源于开源项目：cockroachdb/pebble

Answer 1

This change is