Fix replication lag metric after initial replication #281
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Outdated suggestions cannot be applied.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.
Replication lag metric was introduced in #272 (not released yet).
This fixes an issue where the replication lag metric could keep on growing indefinitely after initial replication, if no other changes come in at that time.
The issue is that in the case of "Commit due to keepalive", the "oldest uncommitted change" was not cleared, even though we have nothing further to write. This fixes the issue.
Sample of what happened:

The sharp increase at 16:23 is when the initial snapshot is completed, and the drop at 17:20 is when another write was made to the source db, clearing the replication lag.