[teiid-issues] [JBoss JIRA] (TEIID-2892) OData buffers ALL rows from resultset before returning the first batch

[Patrick Deenen (JIRA)]

Patrick Deenen created TEIID-2892:
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             Summary: OData buffers ALL rows from resultset before returning the first batch
                 Key: TEIID-2892
                 URL: https://issues.jboss.org/browse/TEIID-2892
             Project: Teiid
          Issue Type: Bug
          Components: OData
    Affects Versions: 8.4.1
         Environment: Tested with Jboss DV 6.0.0. GA (enterprise edition) on Apple OSX 10.9.2 and Oracle Java VM 1.7.0_51.
            Reporter: Patrick Deenen
            Assignee: Steven Hawkins


OData doesn’t batch internally opposed to JDBC which does. E.g. when in JDBC a query is done with a large result, only the first 2048 rows are physically fetched from the source database and only the first 200 rows (depending on client application) are returned. But when the same query is executed by the use of Odata ALL rows in the result set are physically fetched by DV and stored in the buffer. Even with the default Odata fetch batch size of 256. This makes the Odata interface very inefficient for large query results where one only is interessed in the first 256 rows.

Attached you can find two log files which show the problem. 

The Odata query used is:
http://localhost:8080/odata/PMA/EVENT_FACT?$filter=event_fact_id%20ge%20747000000%20and%20event_fact_id%20lt%20747200000

Which is identical to the JDBC query used:
select * from event_fact where event_fact_id between 747000000 and 747200000;

In both cases the result contains 200.000 rows

ODATA log information analysis (log file ’server start + odata batch 256.log’):

row 4543 - 4657   - Start query
row 4658 - 9030   - Read ALL results from result set and store them in buffer
row 9031 - 9035   - Close DB connection
row 9036 - 14647  - Clean buffers and create response?
row 14648 - 14661 - return first batch and close connection

JDBC log information analysis (log file ’server start + jdbc.log’):

row 4925 - 5112   - Start query
row 5113 - 5166   - Read ONLY the first 2048 results from result set and store them in buffer and return response
row 5157 - 5214   - Close DB connection


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