[jira] [Commented] (TORQUE-364) RecordMapper very slow on many columns in table

    [ https://issues.apache.org/jira/browse/TORQUE-364?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17834837#comment-17834837 ] 

Georg Kallidis commented on TORQUE-364:
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Thanks for reporting this issue. To check, if this could be included in the upcoming release and to tackle it down a little bit more, what about it is exactly and what to do, some more information would be helpful:

Indeed mappers are applied for each single row, there is some overhead here, but I could not find any usage of StringBuilder used in any RecordMapper<T> classes. Do yo mean applying some SQL expression e.g. in (always assuming package {{org.apache.torque) in }}{{{}ColumnImpl.ColumnImpl(.. String sqlExpression){}}}? This happens of course already in building the SQL query (e.g {{sql.SqlBuilder.buildQuery(Criteria)) }}in doSelect() methods. The query is indeed build with StringBuilder in {{sql.Query.toStringBuilder(StringBuilder)}}

More generally this may be about some caching mechanism, e.g. applying some kind of save immutable context.

Could you give a more exact example, where this happens most obviously in the Torque template or runtime code? 

> 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.)
> credits to [~refarb] 



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