Max Philipp Wriedt created TORQUE-364:
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Summary: RecordMapper very slow on many columns in table
Key: TORQUE-364
URL: https://issues.apache.org/jira/browse/TORQUE-364
Project: Torque
Issue Type: Improvement
Components: Runtime, Templates
Affects Versions: 5.1
Reporter: Max Philipp Wriedt
When "doSelect()" a large quantity of columns in a table the default
RecordMappers generated by Om-Templates (processRow()) cause an
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Problem. (technically O(rows * columns))
Specifically, constantly generating the SQL expression of all possible columns
for every row in the result causes excessive use of StringBuilders which slow
the mapping process to a crawl.
I currently have two ideas on how best to tackle this problem:
# Either generate all SQL column expressions once when a (template generated)
RecordMapper is first created (using final static String fields) thus reducing
the cost for every row to generating all selected column SQL expressions
once(instead of every selected column times every available column)
# Or (in case the first approach generates unacceptably excessive number of
fields for RecordMappers) adjust the RecordMapper API to allow a
"prepare(Criteria, int offset)" method to be called once before processing any
rows and implement it on generated RecordMappers to scan the Criteria and build
two lists: One containing references to the setXXX methods of the mapper in the
order they appear in the ResultSet (via the order in the Criteria) and a second
list containing the corresponding column offsets. This would allow the
processRow method to only iterated over both lists simultaneously and call the
referenced methods with the result set and offset immediately. (Alternatively
one list using lambdas could be used but I am currently not sure about the
stance or impact of these lambdas in the Torque project.)
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