Would it make sense to have transactional behaviour for status variables, and/or information_schema tables? Or does this break the code and/or user expectations too much? The motivation is to follow up on MWL#116, group commit, which introduces consistent commit order between storage engines and binary log. I want to use this to get a consistent binlog position for START TRANSACTION WITH CONSISTENT SNAPSHOT, without taking any additional locks. Currently, I believe it is common (eg. mysqlbinlog --master-data --single-transaction) to do something like this: FLUSH TABLES WITH READ LOCK; START TRANSACTION WITH CONSISTENT SNAPSHOT; UNLOCK TABLES <take consistent backup by dumping tables using the consistent snapshot> and this takes a lock that can depending on circumstances severely affect the server: http://www.mysqlperformanceblog.com/2010/04/24/how-fast-is-flush-tables-with... One idea is to let the binlog storage engine participate in START TRANSACTION WITH CONSISTENT SNAPSHOT, by installing a start_consistent_snapshot() method in its handlerton. And then do something like this: START TRANSACTION WITH CONSISTENT SNAPSHOT; SELECT variable_value FROM INFORMATION_SCHEMA.SESSION_STATUS WHERE variable_name IN ('binlog_master_file', 'binlog_master_position'); <dump other transactional tables> If the SELECT of binlog_master_file and binlog_master_position could be transactional, then the binlog engine could return the correct values associated with the consistent snapshot, without blocking any other transactions. I like the simplicity of this idea, but I do not understand server transaction handling enough to be sure it will work well, some concerns: - Using SHOW STATUS / INFORMATION_SCHEMA.SESSION_STATUS like this could be surprising to people that do not expect different parts of the results to display different kinds of transactional behaviour. This could be helped by using instead a separate INFORMATION_SCHEMA table for the binlog position. - But this raises another concern, if an INFORMATION_SCHEMA can be transactional in this respect? - Also, it seems to me that merely selecting from such transactional INFORMATION_SCHEMA table would then start a new transaction inside the binlog engine. I wonder if this would cause any unpleasant side effects? Any suggestions or comments? ---- If this does not work, I have another idea, which I think is more general, but also more complicated to implement. The idea is that every transaction has a local transaction ID, assigned at the start (we already have this, in thd->transaction.xid_state.xid). Each engine will transactionally store the local transaction ID of the last transaction committed. The binary log will similarly store this ID along with every transaction that is binlogged. Then START TRANSACTION WITH CONSISTENT SNAPSHOT could optionally return the local transaction ID of the last committed transaction visible in the snapshot obtained. This local transaction ID could then be mapped to binlog position (with eg. mysqldump), and more generally any binlog plugin could provide a way to map such local transaction ID into its own global transaction ID. Similarly, after restore of InnoDB hot backup or LVM snapshot, one could ask the engine for last committed local transaction ID, and map this to binlog position / global transaction ID to be able to use the restored backup to provision a new slave. This would work with any storage engine and any binlog/replication implementation, without any need for FLUSH TABLES WITH READ LOCK. - Kristian.