release-20.1: sqlmigrations: fix handling of mutations in schema change job migration #48838
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The migration for schema change jobs assumed that a table descriptor's `MutationJobs` were always synced with `Mutations`, so we were indexing into `Mutations` with the `MutationJobs` index. In practice, if this assumption doesn't hold due to some previous buggy schema change, we risk crashing with an out of bounds error or looking up the wrong mutation. This PR adds a step to find the mutation with the expected ID and mark the job as failed if the mutation doesn't exist. Release note (bug fix): Fix a problem introduced in v20.1.0 where the migration for ongoing schema change jobs would cause the node to panic with an index out of bounds error, upon encountering a malformed table descriptor with no schema change mutation corresponding to the job to be migrated.
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Backport 1/1 commits from #48823.
/cc @cockroachdb/release
The migration for schema change jobs assumed that a table descriptor's
MutationJobswere always synced withMutations, so we were indexinginto
Mutationswith theMutationJobsindex. In practice, if thisassumption doesn't hold due to some previous buggy schema change, we
risk crashing with an out of bounds error or looking up the wrong
mutation. This PR adds a step to find the mutation with the expected ID
and mark the job as failed if the mutation doesn't exist.
Fixes #48786.
Release note (bug fix): Fix a problem introduced in v20.1.0 where the
migration for ongoing schema change jobs would cause the node to panic
with an index out of bounds error, upon encountering a malformed table
descriptor with no schema change mutation corresponding to the job to be
migrated.