Problem Description

Recipient shards expect to read from the donor shard's existing sharded collection and the config.cache.chunks collection of the temporary resharding collection using {atClusterTime: <fetchTimestamp>}. Refreshing the temporary resharding collection on the donor shards causes them to create the config.cache.chunks.<database>.system.resharding.<existingUUID> collection. If this config.cache.chunks collection is created after the minFetchTimestamp, then the {atClusterTime: <fetchTimestamp>} read on it would fail with a SnapshotUnavailable error response. (Or a NamespaceNotFound error response if the donor shards weren't also recipient shards.)

Donor shards must instead create the config.cache.chunks for temporary resharding collection before calculating their minFetchTimestamp.

Solution

• Trigger a catalog cache refresh for the temporary resharding collection, on the DonorStateMachine, before calculating the fetchTimestamp.
• Remove the refresh that's marked under this ticket's number as a TODO on the coordinator's state machine.