Mongodb – Mongos not returning existing data in shards

Unfortunately there is some stuff that will not be cleaned up through dropDatabase. On the other hand if you delete it by hand may not will be harmful. Some data like statistics will reside on your nodes anyway till the restart of mongods. (Try it out first! Not on the production), as the configuration database is relatively small and does not have huge requirements in terms of performance, that maybe even not a problem, just to be on the safe side and leave them as they are.

Also something to check out how to make the manual actions: https://stackoverflow.com/questions/9407838/mongodb-dropdatabase-not-working

and as it is mentioned on this question the dropDatabase in such case a bit bugy:https://jira.mongodb.org/browse/SERVER-4804

OK, flights.flight is sharded but basically only has one chunk so far, and hence all current data is on one shard and so all writes can only go to one shard - you will need more before the collection can be balanced across multiple shards. Unless you pre-split (something like this) or use a hashed shard key (which you are not) then the mongos process is what is responsible for automatically splitting the chunks.

It will attempt the first split after it has seen writes of approximately 20% of the max chunk size (default is 64MiB, so 20% is ~13MiB). It looks like this has not yet happened, or has failed for some reason in your case.

It should be noted that although the mongos will track all the writes, it will lose its "history" if restarted. It should also be noted that the config servers must be up and working for any splits to happen. Check the mongos logs for any evidence of split failures or similar.

If you want to kick start things manually, just pick two (or more) reasonable split points and use the splitAt() command to break up your current single chunk. You can then wait for the balancer to move things, or you can move them manually with the moveChunk() command. You can find examples of this in the answer to the question I linked above.