Issue #4085
closed
ContentUnitSaver stage is vulnerable to race conditions.
Status:
CLOSED - CURRENTRELEASE
Description
The ContentUnitSaver stage is creating Content using save() and both ContentArtifact and RemoteArtifact using bulk_create() which will raise an IntegretyError on any constraint violation. The same content can be created concurrently during operations such as sync and upload when running more than 1 worker. The race condition exists between the QueryExistingContentUnits and ContentUnitSaver stages. As a result, the un-handled IntegretyError will cause one of the operations to fail.
The impact on users is that syncs will randomly fail with an IntegretyError which will be very concerning.
- Triaged changed from No to Yes
- Sprint set to Sprint 44
This is totally different on the single-content branch which converts the last call to bulk_create() and all of them occur in the transaction. So I think this is maybe NOTABUG. I missed triage so I can only comment now.
- Description updated (diff)
- Sprint deleted (
Sprint 44)
Removing from the sprint due to lack of agreement on around how to handle this.
bmbouter wrote:
This is totally different on the single-content branch which converts the last call to bulk_create() and all of them occur in the transaction. So I think this is maybe NOTABUG. I missed triage so I can only comment now.
What do you mean by "single-content branch" ?
- Related to Issue #4060: QueryExistingArtifacts stage does not prevent duplicates within a stream added
There has been some confusion with this one and https://pulp.plan.io/issues/4060. 4060 is a problem within a single task (sync) of duplicates existing in a stream at the same time. This problem is related, but distinct. As noted in the description, this problem exists when 2 or more tasks are happening at once. If a unit passes through QueryExisting as a non-dupe, and while it is waiting in the Queue for the save stage, and another task creates that unit, it this one becomes a dupe and will fail when it is bulk_saved.
I think it is important to document these problems separately since they occur for different reasons. Some possible solutions might fix both at once. For instance, with docker sync we solve both problems by implementing our own save stage which does not use bulk writes. This allows us to catch and handle integrity errors as they happen. Adding this stage to pulpcore would solve both problems at the expense of database write performance. Since db performance could be a bottleneck, it is worth considering other options if we have any-- but those options would need to take into account both problems (dupes in stream, parallel tasks).
bmbouter, What makes you think that this cannot happen?
worker 1: query content ABC (QueryStage)
not-found
worker 2: query content ABC (QueryStage)
not-found
worker 1: create content ABC (CreateStage)
Inserted
worker 2: create content ABC (CreateStage)
IntegrityError
Recapping some of the discussion from last week, we do need to handle IntegrityErrors-with-requery support in the ContentUnitSaver stage. This ticket can track that. We also need to handle it in the ArtifactSaver stage too, which I believe is tracked as issue https://pulp.plan.io/issues/4060
Does that sound right ^?
I thought @jortel was going to work on a general solution that could be applied to anywhere we call bulk_create and write a ticket for it.
- Related to Refactor #4178: Update sync to use ContentSaver Stage added
- Status changed from NEW to MODIFIED
- Assignee set to dkliban@redhat.com
- Sprint/Milestone set to 3.0.0
- Status changed from MODIFIED to CLOSED - CURRENTRELEASE
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Problem: bulk_create can fail with IntegrityError
Solution: add a manager that provides a bulk_get_or_create() method
This patch introduces a BulkCreateManager that provides the bulk_get_or_create method. This method handles IntegrityErrors encountered during bulk_create() by inserting each object into the database serially. When an IntegrityError or ValueError is encountered during serial saving of objects, the object being saved is replaced with an instance from the database.
This patch introduces a mixin used by Artifact, Content, ContentArtifact, and RemoteArtifact models. The mixin provides the q() method which returns a Q object that can be used to retreive the database instance of the model.
closes #4060 https://pulp.plan.io/issues/4060