When sharding a non-empty collection, whose primary is not the first alphabetically-sorted shard, the Fast Initial Split logic can select wrong shard for the lone initial chunk.
These are the conditions for this issue to occur:
- There is more than one shard (e.g., shard01, shard02)
- The database's primary is not the first alphabetically-sorted shard (shard02 in the example above)
- There are some zones defined for the collection (so the Fast Initial Split optimization is attempted)
- The unsharded collection contains some documents (so that the Fast Initial Split optimization won't kick-in)
In this case, attempting to shard such a collection will wrongly place the only chunk on the first alphabetically-sorted shard, which means none of the documents for that collection will be visible anymore.