Batched join for SELECT sub-queries.

h2/src/main/org/h2/command/dml/Select.java

@@ -948,7 +948,7 @@ public class Select extends Query {
         expressionArray = new Expression[expressions.size()];
         expressions.toArray(expressionArray);
         if (!session.isParsingView()) {
-            topTableFilter.prepareBatch(0);
+            topTableFilter.prepareJoinBatch(0);
         }
         isPrepared = true;
     }

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

@@ -27,9 +27,11 @@ public interface IndexLookupBatch {
      * 
      * @param first the first row, or null for no limit
      * @param last the last row, or null for no limit
+     * @return {@code false} if this search row pair is known to produce no results
+     *          and thus the given row pair was not added
      * @see Index#find(TableFilter, SearchRow, SearchRow)
      */
-    void addSearchRows(SearchRow first, SearchRow last);
+    boolean addSearchRows(SearchRow first, SearchRow last);
 
     /**
      * Check if this batch is full.

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

@@ -24,7 +24,7 @@ public class ViewCursor implements Cursor {
     private final SearchRow first, last;
     private Row current;
 
-    ViewCursor(ViewIndex index, LocalResult result, SearchRow first,
+    public ViewCursor(ViewIndex index, LocalResult result, SearchRow first,
             SearchRow last) {
         this.table = index.getTable();
         this.index = index;

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

@@ -347,6 +347,10 @@ public class ViewIndex extends BaseIndex implements SpatialIndex {
         param.setValue(v);
     }
 
+    public Query getQuery() {
+        return query;
+    }
+
     private Query getQuery(Session session, int[] masks,
             TableFilter[] filters, int filter, SortOrder sortOrder) {
         Query q = prepareSubQuery(querySQL, session, masks, filters, filter, sortOrder, true);

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

@@ -14,12 +14,14 @@ import java.util.concurrent.Future;
 import org.h2.index.Cursor;
 import org.h2.index.IndexCursor;
 import org.h2.index.IndexLookupBatch;
+import org.h2.index.ViewCursor;
 import org.h2.index.ViewIndex;
 import org.h2.message.DbException;
+import org.h2.result.LocalResult;
 import org.h2.result.Row;
 import org.h2.result.SearchRow;
 import org.h2.util.DoneFuture;
-import org.h2.util.IntArray;
+import org.h2.util.LazyFuture;
 import org.h2.util.New;
 import org.h2.value.Value;
 import org.h2.value.ValueLong;
@@ -59,9 +61,8 @@ public final class JoinBatch {
         }
     };
 
-    private static final Future<Cursor> PLACEHOLDER = new DoneFuture<Cursor>(null);
-
     private ViewIndexLookupBatch viewIndexLookupBatch;
+    private Future<Cursor> viewTopFutureCursor;
 
     private JoinFilter[] filters;
     private JoinFilter top;
@@ -157,12 +158,20 @@ public final class JoinBatch {
     private void start() {
         // initialize current row
         current = new JoinRow(new Object[filters.length]);
-        if (viewIndexLookupBatch == null) {
         // initialize top cursor
-            IndexCursor indexCursor = top.filter.getIndexCursor();
-            current.updateRow(top.id, indexCursor, JoinRow.S_NULL, JoinRow.S_CURSOR);
-            indexCursor.find(top.filter.getSession(), top.filter.getIndexConditions());
+        Cursor cursor;
+        if (viewIndexLookupBatch == null) {
+            // it is a top level batched query
+            TableFilter f = top.filter;
+            IndexCursor indexCursor = f.getIndexCursor();
+            indexCursor.find(f.getSession(), f.getIndexConditions());
+            cursor = indexCursor;
+        } else {
+            // we are at the batched sub-query
+            assert viewTopFutureCursor != null;
+            cursor = get(viewTopFutureCursor);
         }
+        current.updateRow(top.id, cursor, JoinRow.S_NULL, JoinRow.S_CURSOR);
         // we need fake first row because batchedNext always will move to the next row
         JoinRow fake = new JoinRow(null);
         fake.next = current;
@@ -204,11 +213,13 @@ public final class JoinBatch {
     }
 
     private static Cursor get(Future<Cursor> f) {
+        Cursor c;
         try {
-            return f.get();
+            c = f.get();
         } catch (Exception e) {
             throw DbException.convert(e);
         }
+        return c == null ? EMPTY_CURSOR : c;
     }
 
     private boolean batchedNext() {
@@ -294,17 +305,23 @@ public final class JoinBatch {
         Object x = current.row(jfId);
         assert x != null : "x null";
 
-        final JoinFilter jf = filters[jfId];
         // in case of outer join we don't have any future around empty cursor
         boolean newCursor = x == EMPTY_CURSOR;
 
-        if (!newCursor && current.isFuture(jfId)) {
+        if (newCursor) {
+            if (jfId == 0) {
+                // the top cursor is new and empty, drop it
+                current.drop();
+                return;
+            }
+        } else if (current.isFuture(jfId)) {
             // get cursor from a future
             x = get((Future<Cursor>) x);
             current.updateRow(jfId, x, JoinRow.S_FUTURE, JoinRow.S_CURSOR);
             newCursor = true;
         }
 
+        final JoinFilter jf = filters[jfId];
         Cursor c = (Cursor) x;
         assert c != null;
         JoinFilter join = jf.join;
@@ -337,10 +354,11 @@ public final class JoinBatch {
             }
             if (c != null) {
                 current = current.copyBehind(jfId);
-                // get current row from cursor
+                // update jf, set current row from cursor
                 current.updateRow(jfId, c.get(), JoinRow.S_CURSOR, JoinRow.S_ROW);
             }
             if (joinEmpty) {
+                // update jf.join, set an empty cursor
                 current.updateRow(join.id, EMPTY_CURSOR, JoinRow.S_NULL, JoinRow.S_CURSOR);
             }
             return;
@@ -348,13 +366,11 @@ public final class JoinBatch {
     }
 
     /**
-     * @return Adapter to allow joining to this batch in sub-queries.
+     * @return Adapter to allow joining to this batch in sub-queries and views.
      */
     public IndexLookupBatch asViewIndexLookupBatch(ViewIndex viewIndex) {
-        if (viewIndexLookupBatch == null) {
-            viewIndexLookupBatch = new ViewIndexLookupBatch(viewIndex);
-        }
-        return viewIndexLookupBatch;
+        assert viewIndexLookupBatch == null;
+        return viewIndexLookupBatch = new ViewIndexLookupBatch(viewIndex);
     }
 
     @Override
@@ -417,8 +433,7 @@ public final class JoinBatch {
             if (c.isAlwaysFalse()) {
                 return false;
             }
-            lookupBatch.addSearchRows(c.getStart(), c.getEnd());
-            return true;
+            return lookupBatch.addSearchRows(c.getStart(), c.getEnd());
         }
 
         private List<Future<Cursor>> find() {
@@ -627,11 +642,12 @@ public final class JoinBatch {
         }
 
         @Override
-        public void addSearchRows(SearchRow first, SearchRow last) {
+        public boolean addSearchRows(SearchRow first, SearchRow last) {
             assert !full;
             this.first = first;
             this.last = last;
             full = true;
+            return true;
         }
 
         @Override
@@ -678,58 +694,131 @@ public final class JoinBatch {
     }
     
     /**
-     * Lookup batch over this join batch for a sub-query or view.
+     * Index lookup batch over this join batch for a sub-query or view.
      */
     private final class ViewIndexLookupBatch implements IndexLookupBatch {
         private final ViewIndex viewIndex;
-        private final IntArray counts = new IntArray();
+        private final ArrayList<Future<Cursor>> result = New.arrayList();
+        private int resultSize;
 
         private ViewIndexLookupBatch(ViewIndex viewIndex) {
             this.viewIndex = viewIndex;
         }
 
-        @Override
-        public void addSearchRows(SearchRow first, SearchRow last) {
-            viewIndex.setupQueryParameters(viewIndex.getSession(), first, last, null);
-            if (top.collectSearchRows()) {
-                if (top.isBatchFull()) {
-                    fetch();
+        private boolean resetAfterFind() {
+            if (resultSize < 0) {
+                // method find was called, we need to reset futures to initial state for reuse
+                for (int i = 0, size = -resultSize; i < size; i++) {
+                    ((QueryRunner) result.get(i)).reset();
                 }
+                resultSize = 0;
+                return true;
             }
+            return false;
         }
 
-        private void fetch() {
-            // TODO
+        @Override
+        public boolean addSearchRows(SearchRow first, SearchRow last) {
+            resetAfterFind();
+            viewIndex.setupQueryParameters(viewIndex.getSession(), first, last, null);
+            if (!top.collectSearchRows()) {
+                return false;
             }
-
-        private void onNextCursorStart() {
-            
+            QueryRunner r;
+            if (resultSize < result.size()) {
+                // get reused runner
+                r = (QueryRunner) result.get(resultSize);
+            } else {
+                // create new runner
+                result.add(r = new QueryRunner());
+            }
+            r.first = first;
+            r.last = last;
+            resultSize++;
+            return true;
         }
 
         @Override
         public boolean isBatchFull() {
-            
+            return top.isBatchFull();
         }
 
         @Override
         public List<Future<Cursor>> find() {
-            state = State.FIND_CALLED;
-            return result;
+            if (resultSize == 0) {
+                return Collections.emptyList();
+            }
+            // we do batched find only for top table filter and then lazily run the ViewIndex query
+            // for each received top future cursor
+            List<Future<Cursor>> topFutureCursors = top.find();
+            if (topFutureCursors.size() != resultSize) {
+                throw DbException.throwInternalError("Unexpected result size: " + result.size() +
+                        ", expected :" + resultSize);
+            }
+            for (int i = 0; i < resultSize; i++) {
+                QueryRunner r = (QueryRunner) result.get(i);
+                r.topFutureCursor = topFutureCursors.get(i);
+            }
+            List<Future<Cursor>> list  = resultSize == result.size() ?
+                    result : result.subList(0, resultSize);
+            // mark that method find was called
+            resultSize = -resultSize;
+            return list;
         }
 
         @Override
         public void reset() {
-            state = State.COLLECTING;
-            result.clear();
-            JoinBatch.this.reset();
+            if (resultSize != 0 && !resetAfterFind()) {
+                // find was not called, need to just clear runners
+                for (int i = 0; i < resultSize; i++) {
+                    ((QueryRunner) result.get(i)).clear();
                 }
+                resultSize = 0;
+            }
+            JoinBatch.this.reset();
         }
 
         /**
-     * State of the ViewIndexLookupBatch 
+         * Lazy query runner.
          */
-    enum State {
-        COLLECTING, FULL, FIND_CALLED
+        private class QueryRunner extends LazyFuture<Cursor> {
+            private Future<Cursor> topFutureCursor;
+            private SearchRow first;
+            private SearchRow last;
+
+            private void clear() {
+                topFutureCursor = null;
+                first = last = null;
+            }
+
+            @Override
+            public boolean reset() {
+                if (super.reset()) {
+                    return true;
+                }
+                // this query runner was never executed, need to clear manually
+                clear();
+                return false;
+            }
+
+            @Override
+            protected Cursor run() throws Exception {
+                if (topFutureCursor == null) {
+                    // if the top cursor is empty then the whole query will produce empty result
+                    return EMPTY_CURSOR;
+                }
+                JoinBatch.this.viewTopFutureCursor = topFutureCursor;
+                LocalResult localResult;
+                try {
+                    localResult = viewIndex.getQuery().query(0);
+                } finally {
+                    JoinBatch.this.viewTopFutureCursor = null;
+                }
+                ViewCursor cursor = new ViewCursor(viewIndex, localResult, first, last);
+                clear();
+                return cursor;
+            }
+        }
     }
 }
 

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

@@ -363,18 +363,21 @@ public class TableFilter implements ColumnResolver {
      * @param id join filter id (index of this table filter in join list)
      * @return join batch if query runs over index which supports batched lookups, {@code null} otherwise
      */
-    public JoinBatch prepareBatch(int id) {
+    public JoinBatch prepareJoinBatch(int id) {
         joinBatch = null;
         joinFilterId = -1;
         JoinBatch jb = null;
         if (join != null) {
-            jb = join.prepareBatch(id + 1);
+            jb = join.prepareJoinBatch(id + 1);
         }
         IndexLookupBatch lookupBatch = null;
-        // the globally top table filter does not need batching, if isAlwaysTopTableFilter is false
-        // then we either not a top table filter or top table filter in a sub-query which is not
-        // top in outer query, thus we need to enable batching here to allow outer query run batched
-        // join against this sub-query
+        // For globally top table filter we don't need to create lookup batch, because
+        // currently it will not be used (this will be shown in ViewIndex.getPlanSQL()). Probably
+        // later on it will make sense to create it to better support X IN (...) conditions,
+        // but this needs to be implemented separately. If isAlwaysTopTableFilter is false
+        // then we either not a top table filter or top table filter in a sub-query, which
+        // in turn is not top in outer query, thus we need to enable batching here to allow
+        // outer query run batched join against this sub-query.
         if (jb == null && select != null && !isAlwaysTopTableFilter(id)) {
             lookupBatch = index.createLookupBatch(this);
             if (lookupBatch != null) {
@@ -387,13 +390,9 @@ public class TableFilter implements ColumnResolver {
             }
             joinBatch = jb;
             joinFilterId = id;
-            // for globally top table filter we don't need to create lookup batch
-            // currently it will not be used, probably later on it will make sense
-            // to create it to better support X IN (...) conditions, but this needs
-            // to be implemented separately
             if (lookupBatch == null && !isAlwaysTopTableFilter(id)) {
-                // index.createLookupBatch will be called only once because jb can be created only if
-                // lookupBatch is not null from the first call above 
+                // index.createLookupBatch will be called at most once because jb can be
+                // created only if lookupBatch is already not null from the call above.
                 lookupBatch = index.createLookupBatch(this);
             }
             jb.register(this, lookupBatch);

h2/src/main/org/h2/util/LazyFuture.java

+/*
+ * Copyright 2004-2014 H2 Group. Multiple-Licensed under the MPL 2.0,
+ * and the EPL 1.0 (http://h2database.com/html/license.html).
+ * Initial Developer: H2 Group
+ */
+package org.h2.util;
+
+import java.util.concurrent.CancellationException;
+import java.util.concurrent.ExecutionException;
+import java.util.concurrent.Future;
+import java.util.concurrent.TimeUnit;
+import org.h2.message.DbException;
+
+/**
+ * Single threaded lazy future. 
+ * 
+ * @param <T>
+ * @author Sergi Vladykin
+ */
+public abstract class LazyFuture<T> implements Future<T> {
+
+    private static final int S_READY = 0;
+    private static final int S_DONE = 1;
+    private static final int S_ERROR = 2;
+    private static final int S_CANCELED = 3;
+    
+    private int state = S_READY;
+    private T result;
+    private Exception error;
+
+    /**
+     * Reset this future to the initial state.
+     * 
+     * @return {@code false} if it was already in initial state 
+     */
+    public boolean reset() {
+        if (state == S_READY) {
+            return false;
+        }
+        state = S_READY;
+        result = null;
+        error = null;
+        return true;
+    }
+
+    /**
+     * Run computation and produce the result.
+     * 
+     * @return the result of computation
+     */
+    protected abstract T run() throws Exception;
+    
+    @Override
+    public boolean cancel(boolean mayInterruptIfRunning) {
+        if (state != S_READY) {
+            return false;
+        }
+        state = S_CANCELED;
+        return true;
+    }
+
+    @Override
+    public T get() throws InterruptedException, ExecutionException {
+        switch (state) {
+        case S_READY:
+            try {
+                result = run();
+                state = S_DONE;
+            } catch (Exception e) {
+                error = e;
+                if (e instanceof InterruptedException) {
+                    throw (InterruptedException) e;
+                }
+                throw new ExecutionException(e);
+            } finally {
+                if (state != S_DONE) {
+                    state = S_ERROR;
+                }
+            }
+            return result;
+        case S_DONE:
+            return result;
+        case S_ERROR:
+            throw new ExecutionException(error);
+        case S_CANCELED:
+            throw new CancellationException();
+        default:
+            throw DbException.throwInternalError();
+        }
+    }
+
+    @Override
+    public T get(long timeout, TimeUnit unit) throws InterruptedException, ExecutionException {
+        return get();
+    }
+
+    @Override
+    public boolean isCancelled() {
+        return state == S_CANCELED;
+    }
+
+    @Override
+    public boolean isDone() {
+        return state == S_DONE;
+    }
+}

h2/src/test/org/h2/test/db/TestTableEngines.java

@@ -1160,10 +1160,11 @@ public class TestTableEngines extends TestBase {
                 }
 
                 @Override
-                public void addSearchRows(SearchRow first, SearchRow last) {
+                public boolean addSearchRows(SearchRow first, SearchRow last) {
                     assert !isBatchFull();
                     searchRows.add(first);
                     searchRows.add(last);
+                    return true;
                 }
 
                 @Override