Max Philipp Wriedt updated TORQUE-364:
    Labels: criteria_api om performance recordmapper templates  (was: )

> 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
>            Priority: Major
>              Labels: criteria_api, om, performance, recordmapper, templates
> When "doSelect()" a large quantity of columns in a table the default 
> RecordMappers generated by Om-Templates (processRow()) cause an  
> !https://wikimedia.org/api/rest_v1/media/math/render/svg/4441d9689c0e6b2c47994e2f587ac5378faeefba!
>  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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