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https://issues.apache.org/jira/browse/CALCITE-3873?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17068247#comment-17068247
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Chunwei Lei commented on CALCITE-3873:
--------------------------------------
Nice job~
> Use global caching for ReflectiveVisitDispatcher implementation
> ---------------------------------------------------------------
>
> Key: CALCITE-3873
> URL: https://issues.apache.org/jira/browse/CALCITE-3873
> Project: Calcite
> Issue Type: Improvement
> Components: core
> Affects Versions: 1.22.0
> Reporter: neoremind
> Priority: Minor
> Labels: pull-request-available
> Attachments: ReflectVisitorDispatcherTest.java, jmh_result.txt,
> pic1.svg, pic2.svg
>
> Time Spent: 2h
> Remaining Estimate: 0h
>
> For curiosity, I use flame graph to profiling a simple query. The code
> snippet looks like below.
> {code:java}
> String sql = "select empno, gender, name from EMPS where name = 'John'";
> Connection connection = null;
> Statement statement = null;
> try {
> Properties info = new Properties();
> info.put("model", jsonPath("smart"));
> connection = DriverManager.getConnection("jdbc:calcite:", info);
> String x = null;
> for (int i = 0; i < 50000; i++) {
> statement = connection.createStatement();
> final ResultSet resultSet =
> statement.executeQuery(
> sql);
> while (resultSet.next()) {
> x = resultSet.getInt(1)
> + resultSet.getString(2)
> + resultSet.getString(3);
> }
> }
> } catch (SQLException e) {
> e.printStackTrace();
> } finally {
> close(connection, statement);
> }
> {code}
>
> I attach the generated flame graph [^pic1.svg]
> {code:java}
> 3% on sql2rel
> 9% on query optimizing,
> 62% of the time is spent on code gen and implementation,
> 20% on result set iterating and checking,
> …
> {code}
> Hope this graph is informative. Since I start to learn Calcite recently, I
> cannot tell where to start tuning, but from the graph one tiny point catches
> my attention, I find there are many reflection invocations in
> _Prepare#trimUnusedFields_. So, I spent some time trying to mitigate the
> small overhead.
> I optimize _ReflectiveVisitDispatcher_ by introducing a global _Guava_ cache
> with limited size to cache methods, also I add full unit tests for
> _ReflectUtil_.
> I count the reference of the method: _ReflectUtil#createMethodDispatcher and_
> _ReflectUtil#createDispatcher (see below)._ Total 68 possible invocations, so
> the cache size is limited, by caching all the methods during the lifecycle of
> the process, we can eliminate reflection looking up methods overhead.
> {code:java}
> org.apache.calcite.rel.rel2sql.RelToSqlConverter: 18 possible invocations.
> org.apache.calcite.sql2rel.RelDecorrelator: 15 possible invocations.
> org.apache.calcite.sql2rel.RelFieldTrimmer: 11 possible invocations.
> org.apache.calcite.sql2rel.RelStructuredTypeFlattener.RewriteRelVisitor: 22
> possible invocations.
> org.apache.calcite.interpreter.Interpreter.CompilerImpl: 2 possible
> invocations.
> {code}
> Before introducing the global caching, caching is shared per
> _ReflectiveVisitDispatcher_ instance, now different
> _ReflectiveVisitDispatcher_ in different thread is able to reuse the cached
> methods.
> See [^pic2.svg], after tuning, _trimUnusedFields_ only takes 0.64% of the
> sampling time compared with 1.38% previously. I think this will help in a lot
> more places.
>
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