neoremind created CALCITE-3873:
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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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