Lock-lesser transitions without additional queries #1
Conversation
This file contains bidirectional Unicode text that may be interpreted or compiled differently than what appears below. To review, open the file in an editor that reveals hidden Unicode characters.
Learn more about bidirectional Unicode characters
#350 @arthurnn opened #350 to reduce the impact of Statesman taking gap locks when using MySQL. The crux of the issue is that MySQL's implementation of REPEATABLE READ can take wide locks when an update touches no rows, which happens frequently on the first transition of Statesman. By first creating the new transition, we can avoid issuing an update that will take the large gap lock. This order of queries meant we added an additional query to the transition step which could impact people who rely on low-latency Statesman transitions. This commit is another take on the same approach that collapses two queries into one, by taking the update of the old and new transition's most_recent column and updating them together. It's slightly janky but if robust, would be a good alternative to avoid additional latency.
Sign up for free
to join this conversation on GitHub.
Already have an account?
Sign in to comment
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Outdated suggestions cannot be applied.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.
gocardless#350
@arthurnn opened gocardless#350 to reduce the impact of Statesman taking gap locks
when using MySQL. The crux of the issue is that MySQL's implementation
of REPEATABLE READ can take wide locks when an update touches no rows,
which happens frequently on the first transition of Statesman.
By first creating the new transition, we can avoid issuing an update
that will take the large gap lock. This order of queries meant we added
an additional query to the transition step which could impact people who
rely on low-latency Statesman transitions.
This commit is another take on the same approach that collapses two
queries into one, by taking the update of the old and new transition's
most_recent column and updating them together. It's slightly janky but
if robust, would be a good alternative to avoid additional latency.