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https://issues.apache.org/jira/browse/TORQUE-364?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17835897#comment-17835897
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Max Philipp Wriedt commented on TORQUE-364:
-------------------------------------------
Regarding point 1:
Our solution with the {{criteria.getSelectColumns().size()}} check only works
if the BaseRecordMapper is used *and* never used by any other custom record
mappers to "chain load". i.e. If I were to implement a FooAndBarMapper which
selects 2 of 5 columns from a table Foo and 3 of 3 columns from a table Bar and
then just call into the FooRecordMapper and BarRecordMapper with appropriate
offsets the check would break and I would get a corrupted Foo object with
garbage data or an exception for storing/reading invalid types from the
ResultSet.
Regarding point 2: The following code should do the thing inside
{{org/apache/torque/templates/om/templates/recordmapper/base/recordMapperBase.vm}}
{code:java}
## Cached SQL expressions to speed up looking for columns selected by a given
Criteria
#foreach ($columnElement in $torqueGen.getChildren("column"))
#set ( $peerColumnName = $columnElement.getAttribute("peerColumnName") )
private static final String ${peerColumnName}_EXPRESSION =
${basePeerClassName}.${peerColumnName}.getSqlExpression();
#end
{code}
As well as
{code:java}
String columnExpression = column.getSqlExpression();
// snip...
${else}if (${peerColumnName}_EXPRESSION.equals(columnExpression))
{code}
In the for each loop over columns
We are currently investigating on point 3 and will provide further information
soon.
As for point 4, improvements are always nice to see.
Regards [~mwriedt] and [~refarb] (<- whose account seems to be missing?)
> 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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