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I wanted to tell you what limitations you may face with statement-based, and why you should join me in making the switch. Statement based binary logging requires additional locking to ensure slave-consistency.
To illustrate, here is a naive example:. Because statements are only written to the binary log once committed, on the slave session 2 would apply first, and result in two rows being updated by session 1, leading to incorrect results!
InnoDB prevents against this race condition by setting additional locking. As the name suggests, this is totally unsupported and you will likely get replication drift. However, astute readers will notice that since row-based replication sends the actual row images of changes to the slaves, this race condition problem no longer exists. Can you see the race-condition? In between each row we need to protect the auto-increment value so nobody could grab one of the IDs, leading to a conflict on the slave as it tries to just use the next number.
This locking is batched-insert only. It previously also applied to single-row inserts, but that was fixed in MySQL 5. You can enable the 5. Row-based events are harder to debug, since you could not previously see the actual statement that generated the row events. This is addressed in MySQL 5. Statement-based replication was an okay choice in the past where we had single-core machines, but today scaling requires us to lock less, and perform more work in parallel.
Have you made the switch? Something else holding you back? Let me know your thoughts in the comments. Like you I made the switch long ago — with the immediate result of eliminating replication drift — no more weird data inconsistencies between master and slaves that I could find. However recently I came back upon the advantages in using SBR; namely the fact that you can create triggers on slaves without creating them on master and that they would actually work.
Both tools rely on triggers. Did I say two? A new tool developed just a couple days ago by my colleague and myself — to be announced shortly. Very interesting functionality, again relying on slave triggers. Shlomi — thanks for commenting! In the case of pt-online-schema-change, I know that it changes back to SBR for the session it runs in which should be enough.
But this is a great point to include. In versions prior to 5. They kind of bloat the log big time though. Remember that UUID events now take up extra space and checksum events too. I try to not tier my slaves when I can.. It probably should be larger. Justin, I actually never did get the full picture: How about the opposite direction?
Personally I think that either this is a bug, or that there should be an option: Gaps and next-key locks are indeed no longer taken. Extra locks from unindexed or not-well-indexed scans, however, are released too.
That is, those locks that did not actually match the WHERE clause but were scanned and thus locked are unlocked. This can get you higher overall concurrency but there is a higher chance of deadlock. Avoiding drift on slaves is a huge reason to switch to row-based replication. That will probably put the nail in the coffin of statement based and bring MySQL replication into the big leagues.
Some additional reasons to use Row-based replication by Ike Walker: Can anyone tell me what the process would be to switch to rbr from an existing system using sbr? Is it as simple as changing the mysql settings or is it best to resync all data after making the change?
The setting is this one, and can be changed at runtime although it includes a warning: I have enabled Row based replication, but create user is being sent to the slave as well. Why is this happening? Skip to content Presentations Translations Contact. Write scalability of certain statements Statement based binary logging requires additional locking to ensure slave-consistency. To illustrate, here is a naive example: Reasons to not use Row-based replication I think the two biggest complaints have always been: Row-based binary logging produces much larger binary log files.
This is largely addressed in 5. Summary Statement-based replication was an okay choice in the past where we had single-core machines, but today scaling requires us to lock less, and perform more work in parallel. View all posts by morgo.
Hi Morgan, and congrats on your new position! Two recent use cases: Deciding whether or not to make MySQL durable.