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MySQL 5.5 Replication Enhancements – An Overview (FOSDEM 2011)
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MySQL 5.5 Replication Enhancements – An Overview
Lenz Grimmer
MySQL Community Relations Specialist
3. Semi-synchronous Replication
• Improves replication resilience and failover
reliability
• Designed as a plugin
• COMMITs on the master node are
acknowledged only when at least one slave
has logged the event in the relay log
• Data is not lost in case of failover
4. Replication Heartbeat
• Message sent at regular intervals from master
node to slave nodes
• Avoids spurious relay log rotation when
master node is idle
• Heartbeats are sent only if there are no more
unsent events in the binlog file
• If message is not received, slave knows that
master node has failed
5. Replication Slave fsync() Options
• Fine tune relay logs and {master|relay-
log}.info fsync operations
• Reduces potential file corruption when slave
crashes
• Three new parameters to configure how often
IO and SQL threads will issue file sync
6. Automatic Relay Log Recovery
• Ensures master/slave consistency on restart
• Slave automatically discard its own
unprocessed relay logs
• Recovers pending transactions from the
originating master
7. Per-master Event Filtering
• MySQL slave can discard events coming from
a specific master
• 'CHANGE MASTER' now supports
'IGNORE_SERVER_IDS = ...' to configure
which events should be discarded
• Useful in circular replication topologies
8. Replication Slave Side Type Conversions
• Row-based replication between columns with
different types was limited
• Type promotion and demotion is now
supported
• Examples:
– Replicate seamlessly from TINYINT column on master
to INT column on the slave
– Or CHAR(10) column to a VARCHAR(20) column
– Or even from TEXT column to VARCHAR(20) column
9. Individual Log Flushing
• Users can now selectively flush server logs
with 'FLUSH LOGS'
• Before, every time users wanted to flush such
logs, other server logs would flush as well
• Now users can specify which individual log to
flush by providing the log type as an argument
to the 'FLUSH LOGS' command
10. SHOW RELAYLOG EVENTS
• You can now show relay log contents, as you
would do for the binlogs
• Useful for comparing events on the master
binlog against the slave relay log
• Easier to inspect the binary and relay logs on
servers that act both as master and slave in
chained replication topologies
• May also be used to diagnose relay log
corruption
11. Give it a spin!
• Download MySQL 5.5 from the usual place:
http://dev.mysql.com/downloads/mysql/
• Send us feedback and bug reports:
http://bugs.mysql.com/
• Questions? Use the Forums or Mailing Lists:
http://forums.mysql.com|http://lists.mysql.com
• Blog about your experiences:
http://planet.mysql.com
