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https://issues.apache.org/jira/browse/NIFI-4385?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16412054#comment-16412054
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Matt Burgess commented on NIFI-4385:
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Max Number of Fragments is a dangerous thing IMO, usually only used as a
stopgap in case you encounter a table larger than you'd expected (and you don't
want to restart NiFi). Does NIFI-4836 solve your use case?
> 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
> Priority: Major
>
> 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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