We have implemented a CSV import fort some large CSV files. The process can be triggered by the user changing a drop down value of a file inside a sharepoint library to "pending". Our importer then sees that and starts importing the file, which takes around 1 hour.
Now we have implemented an automatic import by a daily timer job. The timerjob also simply set's the pending flag to trigger the import. When done this way, the import job runs for around 5 hours - 5 times longer!
I have searched why this could be the case, but found no clue. Somehow I suppose the import now must be running under some other context (timerjob context?) which has maybe lower priority and thus takes much longer.
Otherwise the import result is the same and import finishes successful.