Tim Späth created NIFI-4385:
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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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