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Isn't WAL-based replication more reliable?

• pritambaral 10y ago
  It is. But at least MySQL provides both ways of shipping changes, WAL-shipping like row-based replication and the less reliable statement-based replication, and the DBA can choose which to use when. Combining that fact with the way Postgres and InnoDB handle secondary indexes means WAL-shipping not only ships the entire new row, but also all the disk blocks of all the secondary index updates, unlike MySQL's row-based replication. This is actually something I greatly like and want to see in Postgres. Perhaps the decision to choose secondary indexes with direct links to rows was taken because at that time (before replication) it was less read-heavy and the write-amplification wasn't such a concern. But now, when replication is a common requirement (and network IO is not as fast as disk IO) it makes a lot of sense to switch to a single-point-of-update allowing way of storing secondary indexes