REP-5218 Roll back tasks as needed when restarting. #35
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Commenting here for posterity, this LGTM |
autarch
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Nov 7, 2024
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autarch
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LGTM % I don't really have a ton of context on this code base.
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| func (verifier *Verifier) doInMetaTransaction( | ||
| ctx context.Context, | ||
| todo func(context.Context, mongo.SessionContext) error, |
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nit: I think todo is not the best name, given how we use TODO comments in our code base.
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The worker threads look for status=added tasks when finding work to do. When it grabs a task it sets status=processing; thus, no other threads will try to grab that task.
If the verifier crashes, though, any tasks that were status=processing need to be reset; otherwise no worker thread will ever pick them up, and the verifier will hang.
This changeset implements that reset of status=processing tasks so that the verifier will be able to finish after a restart.
Specifically:
processing, this means that the initial listing of namespaces was interrupted. Thus, we now reset the primary task toadded, and all other tasks are deleted.processing, that means we never finished writing out the collection’s partitions and checking its metadata. Any existing partition tasks are unusuable, so they get deleted, and the collection-verification task is reset toadded.processingpartition tasks are reset toadded.The use of transactions to do these rollbacks means that the verifier’s metadata can no longer be a standalone mongod.