Merge pull request #193 from svladykin/batchFindApi

Batched Index.find API

h2/src/main/org/h2/index/BaseIndex.java

@@ -5,6 +5,8 @@
  */
 package org.h2.index;
 
+import java.util.List;
+import java.util.concurrent.Future;
 import org.h2.api.ErrorCode;
 import org.h2.engine.Constants;
 import org.h2.engine.DbObject;
@@ -424,4 +426,14 @@ public abstract class BaseIndex extends SchemaObjectBase implements Index {
         // ignore
     }
 
+    @Override
+    public int getPreferedLookupBatchSize() {
+        // No batched lookups supported by default.
+        return 0;
+    }
+
+    @Override
+    public List<Future<Cursor>> findBatched(TableFilter filter, List<SearchRow> firstLastPairs) {
+        throw DbException.throwInternalError("Must not be called if getPreferedLookupBatchSize() is 0.");
+    }
 }

h2/src/main/org/h2/index/Index.java

@@ -5,6 +5,8 @@
  */
 package org.h2.index;
 
+import java.util.List;
+import java.util.concurrent.Future;
 import org.h2.engine.Session;
 import org.h2.result.Row;
 import org.h2.result.SearchRow;
@@ -256,4 +258,28 @@ public interface Index extends SchemaObject {
      */
     void setSortedInsertMode(boolean sortedInsertMode);
 
+    /**
+     * If this index can do batched lookups, it may return it's preferred batch size,
+     * otherwise it must return 0.
+     *
+     * @return preferred batch size or 0 if lookup batching is not supported
+     * @see #findBatched(TableFilter, Collection)
+     */
+    int getPreferedLookupBatchSize();
+
+    /**
+     * Do batched lookup over the given collection of {@link SearchRow} pairs as in
+     * {@link #find(TableFilter, SearchRow, SearchRow)}.
+     * <br/><br/>
+     * Correct implementation must always return number of future cursors equal to
+     * {@code firstLastPairs.size() / 2}. Instead of {@link Future} containing empty
+     * {@link Cursor} it is possible to put {@code null} in result list.
+     *
+     * @param filter the table filter
+     * @param firstLastPairs List of batched search row pairs as in
+     *          {@link #find(TableFilter, SearchRow, SearchRow)}, the collection will be reused by H2,
+     *          thus it makes sense to defensively copy contents if needed.
+     * @return batched cursors for respective search row pairs in the same order
+     */
+    List<Future<Cursor>> findBatched(TableFilter filter, List<SearchRow> firstLastPairs);
 }

h2/src/main/org/h2/index/MultiVersionIndex.java

@@ -6,7 +6,8 @@
 package org.h2.index;
 
 import java.util.ArrayList;
-
+import java.util.List;
+import java.util.concurrent.Future;
 import org.h2.api.ErrorCode;
 import org.h2.engine.Database;
 import org.h2.engine.DbObject;
@@ -387,4 +388,13 @@ public class MultiVersionIndex implements Index {
         delta.setSortedInsertMode(sortedInsertMode);
     }
 
+    @Override
+    public int getPreferedLookupBatchSize() {
+        return 0;
+    }
+
+    @Override
+    public List<Future<Cursor>> findBatched(TableFilter filter, List<SearchRow> firstLastPairs) {
+        throw DbException.throwInternalError("Must never be called.");
+    }
 }