Performance improvement for metadata queries that join against the

COLUMNS metatable

h2/src/docsrc/html/changelog.html

@@ -21,6 +21,8 @@ Change Log
 
 <h2>Next Version (unreleased)</h2>
 <ul>
+<li>Performance improvement for metadata queries that join against the COLUMNS metatable
+</li>
 <li>MVStore: power failure could corrupt the store, if writes were re-ordered.
 </li>
 <li>For compatibility with other databases, support for (double and float)

h2/src/main/org/h2/engine/Database.java

@@ -1511,6 +1511,17 @@ public class Database implements DataHandler {
         return list;
     }
 
+    public ArrayList<Table> getTableOrViewByName(String name) {
+      ArrayList<Table> list = New.arrayList();
+      for (Schema schema : schemas.values()) {
+          Table table = schema.getTableOrViewByName(name);
+          if (table != null) {
+          	list.add(table);
+          }
+      }
+      return list;
+  }
+
     public ArrayList<Schema> getAllSchemas() {
         initMetaTables();
         return New.arrayList(schemas.values());

h2/src/main/org/h2/schema/Schema.java

@@ -538,6 +538,13 @@ public class Schema extends DbObjectBase {
         }
     }
 
+    public Table getTableOrViewByName(String name) {
+      synchronized (database) {
+          return tablesAndViews.get(name);
+      }
+    }
+
+
     /**
      * Remove an object from this schema.
      *

h2/src/main/org/h2/table/MetaTable.java

@@ -17,6 +17,7 @@ import java.util.ArrayList;
 import java.util.Collections;
 import java.util.HashMap;
 import java.util.Locale;
+
 import org.h2.command.Command;
 import org.h2.constraint.Constraint;
 import org.h2.constraint.ConstraintCheck;
@@ -615,6 +616,16 @@ public class MetaTable extends Table {
         return tables;
     }
 
+    private ArrayList<Table> getTablesByName(Session session, String tableName) {
+      ArrayList<Table> tables = database.getTableOrViewByName(tableName);
+      for (Table temp : session.getLocalTempTables()) {
+      	if (temp.getName().equals(tableName)) {
+      		tables.add(temp);
+      	}
+      }
+      return tables;
+    }
+
     private boolean checkIndex(Session session, String value, Value indexFrom,
             Value indexTo) {
         if (value == null || (indexFrom == null && indexTo == null)) {
@@ -727,7 +738,15 @@ public class MetaTable extends Table {
             break;
         }
         case COLUMNS: {
-            for (Table table : getAllTables(session)) {
+        	  // reduce the number of tables to scan - makes some metadata queries 10x faster
+        		final ArrayList<Table> tablesToList;
+            if (indexFrom != null && indexTo != null && indexFrom.equals(indexTo)) {
+              String tableName = identifier(indexFrom.getString());
+            	tablesToList = getTablesByName(session, tableName);
+            } else {
+            	tablesToList = getAllTables(session);
+            }
+            for (Table table : tablesToList) {
                 String tableName = identifier(table.getName());
                 if (!checkIndex(session, tableName, indexFrom, indexTo)) {
                     continue;