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From Tim Späth (JIRA) <j...@apache.org>
Subject [jira] [Created] (NIFI-4385) Adjust the QueryDatabaseTable processor for handling big tables.
Date Fri, 15 Sep 2017 10:31:01 GMT
Tim Späth created NIFI-4385:
-------------------------------

             Summary: Adjust the QueryDatabaseTable processor for handling big tables.
                 Key: NIFI-4385
                 URL: https://issues.apache.org/jira/browse/NIFI-4385
             Project: Apache NiFi
          Issue Type: Improvement
          Components: Core Framework
    Affects Versions: 1.3.0
            Reporter: Tim Späth


When querying large database tables, the *QueryDatabaseTable * processor does not perform
very well.
The processor will always perform the full query and then transfer all flowfiles as a list
instead of 
transferring them particularly after the *ResultSet *is fetching the next rows(If a fetch
size is given). 
If you want to query a billion rows from a table, 
the processor will add all flowfiles in an ArrayList<FlowFile> in memory 
before transferring the whole list after the last row is fetched by the ResultSet. 
I've checked the code in *org.apache.nifi.processors.standard.QueryDatabaseTable.java* 
and in my opinion, it would be no big deal to move the session.transfer to a proper position
in the code (into the while loop where the flowfile is added to the list) to 
achieve a real _stream support_. There was also a bug report for this problem 
which resulted in adding the new property *Maximum Number of Fragments*, 
but this property will just limit the results. 
Now you have to multiply *Max Rows Per Flow File* with *Maximum Number of Fragments* to get
your limit, 
which is not really a solution for the original problem imho. 
Also the workaround with GenerateTableFetch and/or ExecuteSQL processors is much slower than
using a database cursor or a ResultSet
and stream the rows in flowfiles directly in the queue.







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