MySQL Replibeertion was the last scheduled session on Day 2, but not withstanding there was free beer (a lot of), there was a serious side with a Replication Discussion.

One of the first questions by Jeremy was “Are the any big replication users?” to which Sheeri quickly replied “Are you calling me fat again”.

This was a highly interactive session, here are some of the points from the audience.

Some Uses of Replication

• Backup
• Hot standby
• Scaling
• Data Warehousing
  • Slaves are larger then your database
• For no special reason
• Consolidation of multiple sources
• Support for multiple indexes

Issues

• Can break
• replication lag
• bi-directional replication is not supported
• hard to setup replication/initialization upto point to run one command
• hard to know when the slave is out of sync (working but broken) diagnose
• does not manage binary logs for you (max-bin-logs )
• no row level replication (5.1 row based replication, change based replication, good and bad )
• Serialized execution on the slave
• Master does not keep track of the slaves (to the master, the slave is just another connection) Jeremy comment “it really really sucks in production systems.”
• No multi-master replication. A slave can not have more then one master.
• ring replication. No idea when something breaks what is right.
• no ability for delayed duplication.
• no way to get binlogs back. (manually twink the info file)
• Master doesn’t care what data is on the slave.
• A replication backup is really only good for the restoration of that machine
• Default reconnection timeout is way, way to high (default of 1 minute). It should be at most 1 second with exponential fallback. (master-connect-retry), no fallback, no max number of retries, logged in error log every time.

Feature Results (Things replication needs, what you want to see)

• Delayed Replication
• Registered Salves in the Master
• Import Binlog
• Checksum Table Events (Need ability for table checksum to be added to binlog periodically so it can be checked by the slave.)
• Global Sequence Number
• Connect Retry Exponential Backoff
• Hetrogous Replication (Oracle to MySQL). Golden Gate Software has a commercial offering
• Command Exclusion List (sql_log_bin=0)
• Replication filters by data on the slave
• Show upcoming queries, skip query
• Multi-Master to one slave
• piping mysqlbin log commands into the mysql client fails for some character sets.
• Binlog index capability
• Checksum of Binary Events to determine a command is valid
• command line interface in mysqllog so you could go backwards and forwards, then execute commands.

Check out more at Google Code Blog.