migrater: reverse_replication and other solidification #5325
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Signed-off-by: Sugu Sougoumarane <ssougou@gmail.com>
Signed-off-by: Sugu Sougoumarane <ssougou@gmail.com>
Signed-off-by: Sugu Sougoumarane <ssougou@gmail.com>
Signed-off-by: Sugu Sougoumarane <ssougou@gmail.com>
Signed-off-by: Sugu Sougoumarane <ssougou@gmail.com>
Signed-off-by: Sugu Sougoumarane <ssougou@gmail.com>
deepthi
approved these changes
Oct 21, 2019
go/vt/wrangler/migrater.go
Outdated
| @@ -157,34 +176,43 @@ func (wr *Wrangler) MigrateWrites(ctx context.Context, targetKeyspace, workflow | |||
| defer targetUnlock(&err) | |||
| } | |||
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| journalsExist, err := mi.checkJournals(ctx) | |||
| // If not journals exist, sourceWorkflows will be initialized by sm.MigrateStreams. | |||
Signed-off-by: Sugu Sougoumarane <ssougou@gmail.com>
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The previous implementation only created the reverse replication streams, but there was no option to start them. This change introduces the flag and the functionality to start the reverse replication.
The overall order of operations have been adjusted to make more logical sense with respect to reverse replication.
The reverse replication now receives a more user friendly
reverse_workflowname which makes things more understandable.This change also addresses a special corner case: once the migration is fully done, the last action is to delete the target vreplication streams. But if this operation fails partially, the user has to manually delete the left over streams. Re-attempting the migrate command will likely result in errors about the streams being inconsistent. This delete is now done in two phases: First, the streams are marked as frozen, and then deleted. This also gives us the opportunity to check for this flag right at the beginning. If we detect that any of the streams are frozen, we directly skip forward and just delete the left over streams.
The migration cancel has also been hardened. It now performs the cancel based on the original data structures that were built. The previous algorithm of re-reading the data separately was confusing and less maintainable.