[GitHub] [calcite] hsyuan commented on a change in pull request #1533: [CALCITE-3446] Make RelMetadataQuery extensible

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hsyuan commented on a change in pull request #1533: [CALCITE-3446] Make RelMetadataQuery extensible
URL: https://github.com/apache/calcite/pull/1533#discussion_r339417872
 
 

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 File path: core/src/main/java/org/apache/calcite/plan/RelOptCluster.java
 ##########
 @@ -135,23 +140,41 @@ public RelMetadataProvider getMetadataProvider() {
   public void setMetadataProvider(RelMetadataProvider metadataProvider) {
     this.metadataProvider = metadataProvider;
     this.metadataFactory = new MetadataFactoryImpl(metadataProvider);
+    // Wrap the metadata provider as a JaninoRelMetadataProvider
+    // and set it to the ThreadLocal,
+    // JaninoRelMetadataProvider is required by the RelMetadataQuery.
+    AbstractRelMetadataQuery.THREAD_PROVIDERS
+        .set(JaninoRelMetadataProvider.of(metadataProvider));
   }
 
   public MetadataFactory getMetadataFactory() {
     return metadataFactory;
   }
 
+  /**
+   * Set up the customized {@link RelMetadataQuery} instance that to use during rule planning.
+   *
+   * <p>Caution that the {@code mqSupplier} should return
+   * a fresh new {@link RelMetadataQuery} instance because the instance would be
+   * cached in this cluster, and we may invalidate and re-generate it
+   * for each {@link RelOptRuleCall} circle.
 
 Review comment:
   circle  -> cycle

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