问题
I am inserting/updating data into a table. The database system does not provide an "Upsert" functionality. Thus I am using a staging table for the insert followed by a merge into the "final" table and finally I am truncating the staging table.
This leads to a race condition. If new data is inserted into the staging table between the merge+truncate this data is lost.
How can I make sure this does not happen?
I have tried to model this via Wait/Notify, but this is not a clean solution either. The queue for the "Put Data into staging table" PutDatabaseRecord processor could be filled and "MergeVertica for Insert/Update" ExecuteSQL could still execute.
回答1:
I would use a MonitorActivity processor with a 60 or 30 sec threshold and use the Inactive output with a Continually Send Messages set to "false".
Have the success of the SQL inserts into staging connection into your MonitorActivity, this way if no activity is seen in the last X seconds he will trigger a flowfile that will start your Merge Process.
Download the template from https://codeshare.io/aJNNkn
来源：https://stackoverflow.com/questions/55479331/how-to-execute-a-processor-only-when-another-processor-is-not-executing