Translations:Manual:Database access/18/en

We use the convention $dbr for read and $dbw for write to help you keep track of whether the database object is a slave (read-only) or a master (read/write). If you write to a slave, the world will explode. Or to be precise, a subsequent write query which succeeded on the master may fail when replicated to the slave due to a unique key collision. Replication on the slave will stop and it may take hours to repair the database and get it back online. Setting read_only in my.cnf on the slave will avoid this scenario, but given the dire consequences, we prefer to have as many checks as possible.