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https://issues.apache.org/jira/browse/NIFI-4385?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17714726#comment-17714726
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Rohit Pawar commented on NIFI-4385:
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[~mattyb149] [~pwicks]
Hello, I have question regarding QueryDatabaseTable ,Actually In mysql I am
trying to use server side cursor streaming by enabling useCursorFetch=true in
connection url , For Implementing batch thing and save nifi from
memory-overflow like thinks ,Example for what I am expecting : data-fetched and
send parallely to next processor(which write data in DB) so that load of memory
not increase .
QueryDatabaseTable - > PutDatabaseRecord
Problem : Througth QueryDatabaseTable I got all data of query about 50k get in
halfsec and placed to Queue and then next processor starts processing
it .
Why QueryDatabaseTable place all data at once ? because I have set the values
for fetchrow=50,batch=5,flowfile=5
Anything I am missing?
> 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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