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https://issues.apache.org/jira/browse/TORQUE-364?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17834961#comment-17834961
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Max Philipp Wriedt commented on TORQUE-364:
-------------------------------------------
I'm currently trying to work myself into this issue again, as this was quite a
while ago.
At that time I was upgrading an old Torque-based project from version 3 to
version 5.
The issue manifested everytime we tried to get every column instead of defining
specific columns to show.
Our project has pretty large number of columns (over 200 at some times).
With debugging turned on, we observed a large number of StringBuilder calls to
create the select statement.
The BaseXXXRecordMapper function {{processRow()}} seems to be always called
with {{{}criteria != null{}}}, even when doing a simple {{doSelect()}}
This results in mapping every column instead of directly using the getters.
Our workaround was to extend the if-else in {{{}processRow(){}}}:
{{if (criteria == null || criteria.getSelectColumns().size() - offset ==
BaseXXXPeer.numColumns)}}
We also added static Strings for every Expression, but I don't remember
exactly, if this improved speed or something.
{{private static final String IDExpression;}}
{{static {}}
{{IDExpression = BaseXXXPeer.ID.getSqlExpression();}}
}
I will take a more detailed look into this with ~refarb in the near future.
> 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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