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