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

[Steven Hawkins (JIRA)]

    [ https://issues.jboss.org/browse/TEIID-2892?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12952072#comment-12952072 ] 

Steven Hawkins commented on TEIID-2892:
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> BTW: It is is good that DV tries to cache query results, but I would not expect that the cache algoritme takes priority over returning the first batch of results to the client directly when they are available.

It does not.

> However need to see if behavior of TYPE_SCROLL_INSENSITIVE is to save all batches before the first batch is returned.

No, scroll insensitive will not pull all results before returning the first batch.  However there is nothing that will inhibit it from processing to completion. So in general it's just a timing issue as to how much will be fetched before the client sees the first batch.  Other than that a transaction can force processing to completion.


                
> 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
>         Attachments: logfiles.zip
>
>
> 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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