http://bdr-project.org/docs/next/logical-vs-physical.html
"It (BDR) has significant advantages - and some disadvantages - when
compared to PostgreSQL's older physical (block-based) streaming or
archive-based replication with warm or hot standby"
What exactly is block based? Changes are recorded in the redo log,
right? Does that mean that in streaming replication, from redo log the
server applies changes at the block level of the data-file. That would
also mean that at any time, both primary and standby would be exactly
same, block by block.