1. A method comprising: migrating, via one or more computing devices, a migration document in a migration shard from a first location to a second location; adding, via the one or more computing devices, a first location identifier associated with the first location of the migration document to metadata associated with the migration shard; adding, via the one or more computing devices, a second location identifier associated with the second location of the migration document to the metadata associated with the migration shard; and adding, via the one or more computing devices, one or more shard identifiers to the metadata associated with the migration shard, each of the one or more shard identifiers corresponding to a shard that includes a document that is referenced by one or more documents in the migration shard.