comments

exec/java-exec/src/main/java/org/apache/drill/exec/ops/FragmentContext.java

@@ -229,6 +229,11 @@ public DrillbitContext getDrillbitContext() {
     return context;
   }
 
+  /**
+   * This method is only used to construt InfoSchemaReader, it is for the reader to get full schema, so here we
+   * are going to return a fully initialized schema tree.
+   * @return root schema's plus
+   */
   public SchemaPlus getFullRootSchema() {
     if (queryContext == null) {
       fail(new UnsupportedOperationException("Schema tree can only be created in root fragment. " +

exec/java-exec/src/main/java/org/apache/drill/exec/ops/QueryContext.java

@@ -163,13 +163,19 @@ public SchemaPlus getRootSchema(final String userName) {
   }
 
   /**
-   *  Create and return a SchemaTree with given <i>schemaConfig</i>.
+   *  Create and return a SchemaTree with given <i>schemaConfig</i> but some schemas (from storage plugins)
+   *  could be initialized later.
    * @param schemaConfig
    * @return
    */
   public SchemaPlus getRootSchema(SchemaConfig schemaConfig) {
     return schemaTreeProvider.createRootSchema(schemaConfig);
   }
+  /**
+   *  Create and return a fully initialized SchemaTree with given <i>schemaConfig</i>.
+   * @param schemaConfig
+   * @return
+   */
 
   public SchemaPlus getFullRootSchema(SchemaConfig schemaConfig) {
     return schemaTreeProvider.createFullRootSchema(schemaConfig);

exec/java-exec/src/main/java/org/apache/drill/exec/planner/sql/DynamicRootSchema.java

@@ -37,13 +37,18 @@
 import org.apache.drill.exec.store.SubSchemaWrapper;
 
 import java.io.IOException;
+import java.util.List;
 import java.util.Map;
 import java.util.NavigableSet;
 import java.util.Set;
 
+/**
+ * This class is to allow us loading schemas from storage plugins later when {@link #getSubSchema(String, boolean)}
+ * is called.
+ */
 public class DynamicRootSchema extends DynamicSchema
     implements CalciteRootSchema {
-
+  private static final org.slf4j.Logger logger = org.slf4j.LoggerFactory.getLogger(DynamicRootSchema.class);
   /** Creates a root schema. */
   DynamicRootSchema(StoragePluginRegistry storages, SchemaConfig schemaConfig) {
     super(null, new RootSchema(), "");
@@ -54,11 +59,11 @@ public class DynamicRootSchema extends DynamicSchema
   @Override
   public CalciteSchema getSubSchema(String schemaName, boolean caseSensitive) {
     CalciteSchema retSchema = getSubSchemaMap().get(schemaName);
-
-    if (retSchema == null) {
-      loadSchemaFactory(schemaName, caseSensitive);
+    if (retSchema != null) {
+      return retSchema;
     }
 
+    loadSchemaFactory(schemaName, caseSensitive);
     retSchema = getSubSchemaMap().get(schemaName);
     return retSchema;
   }
@@ -85,35 +90,45 @@ public void loadSchemaFactory(String schemaName, boolean caseSensitive) {
       StoragePlugin plugin = getSchemaFactories().getPlugin(schemaName);
       if (plugin != null) {
         plugin.registerSchemas(schemaConfig, thisPlus);
+        return;
       }
-      else {
-        //this schema name could be `dfs.tmp`, a 2nd level schema under 'dfs'
-        String[] paths = schemaName.split("\\.");
-        if (paths.length == 2) {
-          plugin = getSchemaFactories().getPlugin(paths[0]);
-          if (plugin != null) {
-            plugin.registerSchemas(schemaConfig, thisPlus);
-          }
 
-          final CalciteSchema secondLevelSchema = getSubSchemaMap().get(paths[0]).getSubSchema(paths[1], caseSensitive);
-          if (secondLevelSchema != null) {
-            SchemaPlus secondlevel = secondLevelSchema.plus();
-            org.apache.drill.exec.store.AbstractSchema drillSchema =
-                secondlevel.unwrap(org.apache.drill.exec.store.AbstractSchema.class);
-            SubSchemaWrapper wrapper = new SubSchemaWrapper(drillSchema);
-            thisPlus.add(wrapper.getName(), wrapper);
+      // we could not find the plugin, the schemaName could be `dfs.tmp`, a 2nd level schema under 'dfs'
+      String[] paths = schemaName.split("\\.");
+      if (paths.length == 2) {
+        plugin = getSchemaFactories().getPlugin(paths[0]);
+        if (plugin == null) {
+          return;
+        }
+
+        // we could find storage plugin for first part(e.g. 'dfs') of schemaName (e.g. 'dfs.tmp')
+        // register schema for this storage plugin to 'this'.
+        plugin.registerSchemas(schemaConfig, thisPlus);
+
+        // we load second level schemas for this storage plugin
+        final SchemaPlus firstlevelSchema = thisPlus.getSubSchema(paths[0]);
+        final List<SchemaPlus> secondLevelSchemas = Lists.newArrayList();
+        for (String secondLevelSchemaName : firstlevelSchema.getSubSchemaNames()) {
+          secondLevelSchemas.add(firstlevelSchema.getSubSchema(secondLevelSchemaName));
+        }
+
+        for (SchemaPlus schema : secondLevelSchemas) {
+          org.apache.drill.exec.store.AbstractSchema drillSchema;
+          try {
+            drillSchema = schema.unwrap(org.apache.drill.exec.store.AbstractSchema.class);
+          } catch (ClassCastException e) {
+            throw new RuntimeException(String.format("Schema '%s' is not expected under root schema", schema.getName()));
           }
+          SubSchemaWrapper wrapper = new SubSchemaWrapper(drillSchema);
+          thisPlus.add(wrapper.getName(), wrapper);
         }
       }
     } catch(ExecutionSetupException | IOException ex) {
+      logger.warn("Failed to load schema for \"" + schemaName + "\"!", ex);
     }
   }
 
   static class RootSchema extends AbstractSchema {
-    RootSchema() {
-      super();
-    }
-
     @Override public Expression getExpression(SchemaPlus parentSchema,
                                               String name) {
       return Expressions.call(

exec/java-exec/src/main/java/org/apache/drill/exec/store/SchemaTreeProvider.java

@@ -20,7 +20,6 @@
 import java.io.IOException;
 import java.util.List;
 
-//import org.apache.calcite.jdbc.SimpleCalciteSchema;
 import org.apache.calcite.schema.SchemaPlus;
 import org.apache.drill.common.AutoCloseables;
 import org.apache.drill.common.exceptions.UserException;

exec/java-exec/src/main/java/org/apache/drill/exec/store/dfs/FileSystemSchemaFactory.java

@@ -53,12 +53,14 @@ public class FileSystemSchemaFactory implements SchemaFactory{
 
   public static final String DEFAULT_WS_NAME = "default";
 
+  public static final String LOCAL_FS_SCHEME = "file";
+
   private List<WorkspaceSchemaFactory> factories;
   private String schemaName;
   protected FileSystemPlugin plugin;
 
   public FileSystemSchemaFactory(String schemaName, List<WorkspaceSchemaFactory> factories) {
-    super();
+    // when the correspondent FileSystemPlugin is not passed in, we dig into ANY workspace factory to get it.
     if (factories.size() > 0 ) {
       this.plugin = factories.get(0).getPlugin();
     }
@@ -67,7 +69,6 @@ public FileSystemSchemaFactory(String schemaName, List<WorkspaceSchemaFactory> f
   }
 
   public FileSystemSchemaFactory(FileSystemPlugin plugin, String schemaName, List<WorkspaceSchemaFactory> factories) {
-    super();
     this.plugin = plugin;
     this.schemaName = schemaName;
     this.factories = factories;

exec/java-exec/src/main/java/org/apache/drill/exec/store/dfs/WorkspaceSchemaFactory.java

@@ -170,7 +170,7 @@ public boolean accessible(DrillFileSystem fs) throws IOException {
        * In this case, we will still use method listStatus.
        * In other cases, we use access method since it is cheaper.
        */
-      if (SystemUtils.IS_OS_WINDOWS && fs.getUri().getScheme().equalsIgnoreCase("file")) {
+      if (SystemUtils.IS_OS_WINDOWS && fs.getUri().getScheme().equalsIgnoreCase(FileSystemSchemaFactory.LOCAL_FS_SCHEME)) {
         fs.listStatus(wsPath);
       }
       else {
@@ -572,10 +572,10 @@ public boolean isMutable() {
     }
 
     public DrillFileSystem getFS() {
-      if (this.fs == null) {
-        this.fs = ImpersonationUtil.createFileSystem(schemaConfig.getUserName(), fsConf);
+      if (fs == null) {
+        fs = ImpersonationUtil.createFileSystem(schemaConfig.getUserName(), fsConf);
       }
-      return this.fs;
+      return fs;
     }
 
     public String getDefaultLocation() {