Merge pull request #1192 from metamx/fix-bad-rebase

fix file missing from previous PR rebase

processing/src/main/java/io/druid/segment/SingleScanTimeDimSelector.java

@@ -0,0 +1,136 @@
+/*
+ * Licensed to Metamarkets Group Inc. (Metamarkets) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  Metamarkets licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ *   http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing,
+ * software distributed under the License is distributed on an
+ * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+ * KIND, either express or implied.  See the License for the
+ * specific language governing permissions and limitations
+ * under the License.
+ */
+
+package io.druid.segment;
+
+import com.google.common.collect.Iterators;
+import com.google.common.collect.Maps;
+import io.druid.query.extraction.ExtractionFn;
+import io.druid.segment.data.IndexedInts;
+
+import java.util.Iterator;
+import java.util.Map;
+
+public class SingleScanTimeDimSelector implements DimensionSelector
+{
+  private final ExtractionFn extractionFn;
+  private final LongColumnSelector selector;
+
+  private final Map<Integer, String> timeValues = Maps.newHashMap();
+  private String currentValue = null;
+  private long currentTimestamp = Long.MIN_VALUE;
+  private int index = -1;
+
+
+  // Use a special DimSelector for projected time columns
+  // - it assumes time values are scanned once and values are grouped together
+  //   (i.e. we never revisit a timestamp we have seen before, unless it is the same as the last accessed one)
+  // - it also applies and caches extraction function values at the DimSelector level to speed things up
+  public SingleScanTimeDimSelector(LongColumnSelector selector, ExtractionFn extractionFn)
+  {
+    if (extractionFn == null) {
+      throw new UnsupportedOperationException("time dimension must provide an extraction function");
+    }
+
+    this.extractionFn = extractionFn;
+    this.selector = selector;
+  }
+
+  @Override
+  public IndexedInts getRow()
+  {
+    // if this the first timestamp, apply and cache extraction function result
+    final long timestamp = selector.get();
+    if (index < 0) {
+      currentTimestamp = timestamp;
+      currentValue = extractionFn.apply(timestamp);
+      ++index;
+      timeValues.put(index, currentValue);
+    }
+    // if this is a new timestamp, apply and cache extraction function result
+    // since timestamps are assumed grouped and scanned once, we only need to
+    // check if the current timestamp is different than the current timestamp.
+    //
+    // If this new timestamp is mapped to the same value by the extraction function,
+    // we can also avoid creating a dimension value and corresponding index
+    // and use the current one
+    else if (timestamp != currentTimestamp) {
+      if(timestamp < currentTimestamp) {
+        // re-using this selector for multiple scans would cause the same rows to return different IDs
+        // we might want to re-visit if we ever need to do multiple scans with this dimension selector
+        throw new IllegalStateException("cannot re-use time dimension selector for multiple scans");
+      }
+      currentTimestamp = timestamp;
+      final String value = extractionFn.apply(timestamp);
+      if (!value.equals(currentValue)) {
+        currentValue = value;
+        ++index;
+        timeValues.put(index, currentValue);
+      }
+      // Note: this could be further optimized by checking if the new value is one we have
+      // previously seen, but would require keeping track of both the current and the maximum index
+    }
+    // otherwise, if the current timestamp is the same as the previous timestamp,
+    // keep using the same dimension value index
+
+    final int dimensionValueIndex = index;
+    return new IndexedInts()
+    {
+      @Override
+      public int size()
+      {
+        return 1;
+      }
+
+      @Override
+      public int get(int i)
+      {
+        return dimensionValueIndex;
+      }
+
+      @Override
+      public Iterator<Integer> iterator()
+      {
+        return Iterators.singletonIterator(dimensionValueIndex);
+      }
+    };
+  }
+
+  @Override
+  public int getValueCardinality()
+  {
+    return Integer.MAX_VALUE;
+  }
+
+  @Override
+  public String lookupName(int id)
+  {
+    if (id == index) {
+      return currentValue;
+    } else {
+      return timeValues.get(id);
+    }
+  }
+
+  @Override
+  public int lookupId(String name)
+  {
+    throw new UnsupportedOperationException("time column does not support lookups");
+  }
+}