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https://issues.jboss.org/browse/TEIID-2892?page=com.atlassian.jira.plugin...
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Steven Hawkins commented on TEIID-2892:
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So the full comparison to make is a JDBC query with a scroll insensitive resultset vs. the
OData query. You can get a rough idea of the OData overhead if you repeat this process
for various data widths. I am not certain how much overhead to expect.
You can also compare a forward only JDBC query to scroll insensitive query. This will
give an estimate of the overhead of the more proactive processing associated with a
scrolling result - which could be quite significant for larger results.
From what I can see there isn't a good reason to use scroll
insensitive when we aren't obtaining the row count, so that would be a likely change.
We also may need to revisit the data flow into output buffers even with a transaction or a
scrolling result, as allowing unfettered buffering may be an general problem.
OData buffers ALL rows from resultset before returning the first
batch
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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%207...
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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