Concurrency issue when updating projection version #49
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
added 2 commits
February 9, 2023 11:49
|
I believe we hit this concurrency issue today. We had a duplicate list item projected to a JSONB field. Our only explanation is the same event being projected twice. |
Comment on lines
+69
to
+92
| |> Ecto.Multi.insert_all( | ||
| :insert_version, | ||
| ProjectionVersion, | ||
| [ | ||
| %{ | ||
| inserted_at: DateTime.to_naive(DateTime.utc_now()), | ||
| updated_at: DateTime.to_naive(DateTime.utc_now()), | ||
| projection_name: projection_name, | ||
| last_seen_event_number: 0 | ||
| } | ||
| ], | ||
| on_conflict: :nothing, | ||
| prefix: prefix | ||
| ) | ||
| |> Ecto.Multi.update_all( | ||
| :update_version, | ||
| from(version in ProjectionVersion, | ||
| select: version, | ||
| where: version.projection_name == ^projection_name, | ||
| where: version.last_seen_event_number < ^event_number | ||
| ), | ||
| [set: [last_seen_event_number: event_number]], | ||
| prefix: prefix | ||
| ) |
There was a problem hiding this comment.
These two separate INSERT and UPDATE statements will need to be combined as a single UPSERT query otherwise there is still the possibilty of a concurrency issue due to executing two queries.
|
Implemented as an "UPSERT" SQL query in #52. |
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Outdated suggestions cannot be applied.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.
Concurrency issue when updating projection version.
The problem can occur because the existing projection version is fetched before the update transaction. In rare cases we have seen events being executed twice because of this.
The solution, as implemented in this PR, is to both fetch and update the projection version within the same transaction.