# Issue
MAAS environment with 2 separate controllers. Old controller A has 4GB RAM and a model with about 40 machines. Controller B is an empty controller with 8GB RAM. Trying to migrate the model from A to B stops after a few seconds with with the message "migration: aborted, removing model from target controller" when running "juju show-model".
# Logs machine-0.log from controller A
2017-02-28 14:25:40 ERROR juju.worker.migrationmaster.40fd7e worker.go:284 model data transfer failed, model export failed: failed to read status history collection: Executor error during find command: OperationFailed: Sort operation used more than the maximum 33554432 bytes of RAM. Add an index, or specify a smaller limit.
2017-02-28 14:25:40 WARNING juju.worker.migrationmaster.40fd7e worker.go:592 failed to remove model from target controller, model not found (not found)
# Versions
Juju 2.1.0
MAAS 2.1.3
Any tips for further troubleshooting?
This error means that when we query the status history to export it we're sorting by columns that don't match the available indexes in Mongo.
Looking in the code I can see that the index on the statuseshistory collection is {"model-uuid", "globalkey", "updated"}, but in the export we're sorting by {"-updated", "-_id"} (after filtering by model-uuid).
I think one way to fix it would be to add an index on {"model-uuid", "-updated", "-_id"}. (Maybe we could fix it by querying slightly differently instead.)
The statuseshistory collection should be being trimmed by the status history pruner - can you see any messages in the logs about that? Maybe some indication of how big the collection is?