perf(benchmarks): Add JMH benchmark for Calcite SQL planning path

Add UnifiedSqlQueryBenchmark with SQL equivalents of existing PPL
benchmarks for plan, transpile, and compile operations.

Signed-off-by: Chen Dai <daichen@amazon.com>

Author: dai-chen

benchmarks/src/jmh/java/org/opensearch/sql/api/UnifiedSqlQueryBenchmark.java

@@ -0,0 +1,88 @@
+/*
+ * Copyright OpenSearch Contributors
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+package org.opensearch.sql.api;
+
+import java.sql.PreparedStatement;
+import java.util.concurrent.TimeUnit;
+import org.apache.calcite.rel.RelNode;
+import org.apache.calcite.sql.dialect.SparkSqlDialect;
+import org.openjdk.jmh.annotations.Benchmark;
+import org.openjdk.jmh.annotations.BenchmarkMode;
+import org.openjdk.jmh.annotations.Fork;
+import org.openjdk.jmh.annotations.Level;
+import org.openjdk.jmh.annotations.Measurement;
+import org.openjdk.jmh.annotations.Mode;
+import org.openjdk.jmh.annotations.OutputTimeUnit;
+import org.openjdk.jmh.annotations.Param;
+import org.openjdk.jmh.annotations.Scope;
+import org.openjdk.jmh.annotations.Setup;
+import org.openjdk.jmh.annotations.State;
+import org.openjdk.jmh.annotations.TearDown;
+import org.openjdk.jmh.annotations.Warmup;
+import org.opensearch.sql.api.compiler.UnifiedQueryCompiler;
+import org.opensearch.sql.api.transpiler.UnifiedQueryTranspiler;
+import org.opensearch.sql.executor.QueryType;
+
+/**
+ * JMH benchmark for measuring the overhead of the Calcite native SQL planning path. Provides
+ * baseline metrics comparable to the PPL benchmarks in {@link UnifiedQueryBenchmark}.
+ */
+@Warmup(iterations = 2, time = 1)
+@Measurement(iterations = 5, time = 1)
+@BenchmarkMode(Mode.AverageTime)
+@OutputTimeUnit(TimeUnit.MILLISECONDS)
+@State(Scope.Thread)
+@Fork(value = 1)
+public class UnifiedSqlQueryBenchmark extends UnifiedQueryTestBase {
+
+  @Param({
+    "SELECT * FROM catalog.employees",
+    "SELECT * FROM catalog.employees WHERE age > 30",
+    "SELECT department, count(*) FROM catalog.employees GROUP BY department",
+    "SELECT * FROM catalog.employees ORDER BY age DESC",
+    "SELECT * FROM catalog.employees WHERE age > 25 GROUP BY department ORDER BY department"
+  })
+  private String query;
+
+  private UnifiedQueryTranspiler transpiler;
+  private UnifiedQueryCompiler compiler;
+
+  @Override
+  protected QueryType queryType() {
+    return QueryType.SQL;
+  }
+
+  @Setup(Level.Trial)
+  public void setUpBenchmark() {
+    super.setUp();
+    transpiler = UnifiedQueryTranspiler.builder().dialect(SparkSqlDialect.DEFAULT).build();
+    compiler = new UnifiedQueryCompiler(context);
+  }
+
+  @TearDown(Level.Trial)
+  public void tearDownBenchmark() throws Exception {
+    super.tearDown();
+  }
+
+  @Benchmark
+  public RelNode planQuery() {
+    return planner.plan(query);
+  }
+
+  @Benchmark
+  public String transpileToSql() {
+    RelNode plan = planner.plan(query);
+    return transpiler.toSql(plan);
+  }
+
+  @Benchmark
+  public void compileQuery() throws Exception {
+    RelNode plan = planner.plan(query);
+    try (PreparedStatement stmt = compiler.compile(plan)) {
+      // Statement is auto-closed after benchmark iteration
+    }
+  }
+}