MCOL-5603 Online alter can break data consistency #3021
Add this suggestion to a batch that can be applied as a single commit.
This suggestion is invalid because no changes were made to the code.
Suggestions cannot be applied while the pull request is closed.
Suggestions cannot be applied while viewing a subset of changes.
Only one suggestion per line can be applied in a batch.
Add this suggestion to a batch that can be applied as a single commit.
Applying suggestions on deleted lines is not supported.
You must change the existing code in this line in order to create a valid suggestion.
Outdated suggestions cannot be applied.
This suggestion has been applied or marked resolved.
Suggestions cannot be applied from pending reviews.
Suggestions cannot be applied on multi-line comments.
Suggestions cannot be applied while the pull request is queued to merge.
Suggestion cannot be applied right now. Please check back later.
Propagate the TL lock to TL_READ_NO_INSERT, blocking any concurrent writes until the end of a copy stage.
After that, this lock will be unlocked, allowing a window to write into a table before MDL is upgraded to exclusive (see online_alter_read_from_binlog call and the "alter_table_online_before_lock" debug syncpoint). This window will be covered by the second replication iteration after the lock upgrade