[jira] [Created] (CALCITE-3873) Use global caching for ReflectiveVisitDispatcher implementation

["neoremind (Jira)" <ji...@apache.org>]

neoremind created CALCITE-3873:
----------------------------------

             Summary: 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
         Attachments: pic1.svg, pic2.svg

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;
      long start = System.currentTimeMillis();
      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 static class 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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