Speed up String first/last aggregators when folding isn't needed.

core/src/main/java/org/apache/druid/java/util/common/StringUtils.java

@@ -550,8 +550,8 @@ public static String rpad(String base, Integer len, String pad)
    * Returns the string truncated to maxBytes.
    * If given string input is shorter than maxBytes, then it remains the same.
    *
-   * @param s The input string to possibly be truncated
-   * @param maxBytes  The max bytes that string input will be truncated to
+   * @param s        The input string to possibly be truncated
+   * @param maxBytes The max bytes that string input will be truncated to
    *
    * @return the string after truncated to maxBytes
    */
@@ -568,4 +568,17 @@ public static String chop(@Nullable final String s, final int maxBytes)
     }
   }
 
+  /**
+   * Shorten "s" to "maxBytes" chars. Fast and loose because these are *chars* not *bytes*. Use
+   * {@link #chop(String, int)} for slower, but accurate chopping.
+   */
+  @Nullable
+  public static String fastLooseChop(@Nullable final String s, final int maxBytes)
+  {
+    if (s == null || s.length() <= maxBytes) {
+      return s;
+    } else {
+      return s.substring(0, maxBytes);
+    }
+  }
 }

core/src/test/java/org/apache/druid/java/util/common/StringUtilsTest.java

@@ -246,4 +246,32 @@ public void testRpad()
     Assert.assertEquals(s5, null);
   }
 
+  @Test
+  public void testChop()
+  {
+    Assert.assertEquals("foo", StringUtils.chop("foo", 5));
+    Assert.assertEquals("fo", StringUtils.chop("foo", 2));
+    Assert.assertEquals("", StringUtils.chop("foo", 0));
+    Assert.assertEquals("smile 🙂 for", StringUtils.chop("smile 🙂 for the camera", 14));
+    Assert.assertEquals("smile 🙂", StringUtils.chop("smile 🙂 for the camera", 10));
+    Assert.assertEquals("smile ", StringUtils.chop("smile 🙂 for the camera", 9));
+    Assert.assertEquals("smile ", StringUtils.chop("smile 🙂 for the camera", 8));
+    Assert.assertEquals("smile ", StringUtils.chop("smile 🙂 for the camera", 7));
+    Assert.assertEquals("smile ", StringUtils.chop("smile 🙂 for the camera", 6));
+    Assert.assertEquals("smile", StringUtils.chop("smile 🙂 for the camera", 5));
+  }
+
+  @Test
+  public void testFastLooseChop()
+  {
+    Assert.assertEquals("foo", StringUtils.fastLooseChop("foo", 5));
+    Assert.assertEquals("fo", StringUtils.fastLooseChop("foo", 2));
+    Assert.assertEquals("", StringUtils.fastLooseChop("foo", 0));
+    Assert.assertEquals("smile 🙂 for", StringUtils.fastLooseChop("smile 🙂 for the camera", 12));
+    Assert.assertEquals("smile 🙂 ", StringUtils.fastLooseChop("smile 🙂 for the camera", 9));
+    Assert.assertEquals("smile 🙂", StringUtils.fastLooseChop("smile 🙂 for the camera", 8));
+    Assert.assertEquals("smile \uD83D", StringUtils.fastLooseChop("smile 🙂 for the camera", 7));
+    Assert.assertEquals("smile ", StringUtils.fastLooseChop("smile 🙂 for the camera", 6));
+    Assert.assertEquals("smile", StringUtils.fastLooseChop("smile 🙂 for the camera", 5));
+  }
 }

processing/src/main/java/org/apache/druid/query/aggregation/first/StringFirstAggregator.java

@@ -25,28 +25,29 @@
 import org.apache.druid.query.aggregation.SerializablePairLongString;
 import org.apache.druid.segment.BaseLongColumnValueSelector;
 import org.apache.druid.segment.BaseObjectColumnValueSelector;
-
-import javax.annotation.Nullable;
+import org.apache.druid.segment.DimensionHandlerUtils;
 
 public class StringFirstAggregator implements Aggregator
 {
-  @Nullable
   private final BaseLongColumnValueSelector timeSelector;
-  private final BaseObjectColumnValueSelector valueSelector;
+  private final BaseObjectColumnValueSelector<?> valueSelector;
   private final int maxStringBytes;
+  private final boolean needsFoldCheck;
 
   protected long firstTime;
   protected String firstValue;
 
   public StringFirstAggregator(
-      @Nullable BaseLongColumnValueSelector timeSelector,
-      BaseObjectColumnValueSelector valueSelector,
-      int maxStringBytes
+      BaseLongColumnValueSelector timeSelector,
+      BaseObjectColumnValueSelector<?> valueSelector,
+      int maxStringBytes,
+      boolean needsFoldCheck
   )
   {
     this.valueSelector = valueSelector;
     this.timeSelector = timeSelector;
     this.maxStringBytes = maxStringBytes;
+    this.needsFoldCheck = needsFoldCheck;
 
     firstTime = DateTimes.MAX.getMillis();
     firstValue = null;
@@ -55,17 +56,28 @@ public StringFirstAggregator(
   @Override
   public void aggregate()
   {
-    final SerializablePairLongString inPair = StringFirstLastUtils.readPairFromSelectors(
-        timeSelector,
-        valueSelector
-    );
+    if (needsFoldCheck) {
+      // Less efficient code path when folding is a possibility (we must read the value selector first just in case
+      // it's a foldable object).
+      final SerializablePairLongString inPair = StringFirstLastUtils.readPairFromSelectors(
+          timeSelector,
+          valueSelector
+      );
+
+      if (inPair != null && inPair.rhs != null && inPair.lhs < firstTime) {
+        firstTime = inPair.lhs;
+        firstValue = StringUtils.fastLooseChop(inPair.rhs, maxStringBytes);
+      }
+    } else {
+      final long time = timeSelector.getLong();
 
-    if (inPair != null && inPair.rhs != null && inPair.lhs < firstTime) {
-      firstTime = inPair.lhs;
-      firstValue = inPair.rhs;
+      if (time < firstTime) {
+        final String value = DimensionHandlerUtils.convertObjectToString(valueSelector.getObject());
 
-      if (firstValue.length() > maxStringBytes) {
-        firstValue = firstValue.substring(0, maxStringBytes);
+        if (value != null) {
+          firstTime = time;
+          firstValue = StringUtils.fastLooseChop(value, maxStringBytes);
+        }
       }
     }
   }

processing/src/main/java/org/apache/druid/query/aggregation/first/StringFirstAggregatorFactory.java

@@ -32,6 +32,7 @@
 import org.apache.druid.query.aggregation.BufferAggregator;
 import org.apache.druid.query.aggregation.SerializablePairLongString;
 import org.apache.druid.query.cache.CacheKeyBuilder;
+import org.apache.druid.segment.BaseObjectColumnValueSelector;
 import org.apache.druid.segment.ColumnSelectorFactory;
 import org.apache.druid.segment.column.ColumnHolder;
 
@@ -118,20 +119,24 @@ public StringFirstAggregatorFactory(
   @Override
   public Aggregator factorize(ColumnSelectorFactory metricFactory)
   {
+    final BaseObjectColumnValueSelector<?> valueSelector = metricFactory.makeColumnValueSelector(fieldName);
     return new StringFirstAggregator(
         metricFactory.makeColumnValueSelector(ColumnHolder.TIME_COLUMN_NAME),
-        metricFactory.makeColumnValueSelector(fieldName),
-        maxStringBytes
+        valueSelector,
+        maxStringBytes,
+        StringFirstLastUtils.selectorNeedsFoldCheck(valueSelector, metricFactory.getColumnCapabilities(fieldName))
     );
   }
 
   @Override
   public BufferAggregator factorizeBuffered(ColumnSelectorFactory metricFactory)
   {
+    final BaseObjectColumnValueSelector<?> valueSelector = metricFactory.makeColumnValueSelector(fieldName);
     return new StringFirstBufferAggregator(
         metricFactory.makeColumnValueSelector(ColumnHolder.TIME_COLUMN_NAME),
-        metricFactory.makeColumnValueSelector(fieldName),
-        maxStringBytes
+        valueSelector,
+        maxStringBytes,
+        StringFirstLastUtils.selectorNeedsFoldCheck(valueSelector, metricFactory.getColumnCapabilities(fieldName))
     );
   }
 

processing/src/main/java/org/apache/druid/query/aggregation/first/StringFirstBufferAggregator.java

@@ -25,6 +25,7 @@
 import org.apache.druid.query.monomorphicprocessing.RuntimeShapeInspector;
 import org.apache.druid.segment.BaseLongColumnValueSelector;
 import org.apache.druid.segment.BaseObjectColumnValueSelector;
+import org.apache.druid.segment.DimensionHandlerUtils;
 
 import java.nio.ByteBuffer;
 
@@ -36,18 +37,21 @@ public class StringFirstBufferAggregator implements BufferAggregator
   );
 
   private final BaseLongColumnValueSelector timeSelector;
-  private final BaseObjectColumnValueSelector valueSelector;
+  private final BaseObjectColumnValueSelector<?> valueSelector;
   private final int maxStringBytes;
+  private final boolean needsFoldCheck;
 
   public StringFirstBufferAggregator(
       BaseLongColumnValueSelector timeSelector,
-      BaseObjectColumnValueSelector valueSelector,
-      int maxStringBytes
+      BaseObjectColumnValueSelector<?> valueSelector,
+      int maxStringBytes,
+      boolean needsFoldCheck
   )
   {
     this.timeSelector = timeSelector;
     this.valueSelector = valueSelector;
     this.maxStringBytes = maxStringBytes;
+    this.needsFoldCheck = needsFoldCheck;
   }
 
   @Override
@@ -59,20 +63,40 @@ public void init(ByteBuffer buf, int position)
   @Override
   public void aggregate(ByteBuffer buf, int position)
   {
-    final SerializablePairLongString inPair = StringFirstLastUtils.readPairFromSelectors(
-        timeSelector,
-        valueSelector
-    );
+    if (needsFoldCheck) {
+      // Less efficient code path when folding is a possibility (we must read the value selector first just in case
+      // it's a foldable object).
+      final SerializablePairLongString inPair = StringFirstLastUtils.readPairFromSelectors(
+          timeSelector,
+          valueSelector
+      );
 
-    if (inPair != null && inPair.rhs != null) {
+      if (inPair != null && inPair.rhs != null) {
+        final long firstTime = buf.getLong(position);
+        if (inPair.lhs < firstTime) {
+          StringFirstLastUtils.writePair(
+              buf,
+              position,
+              new SerializablePairLongString(inPair.lhs, inPair.rhs),
+              maxStringBytes
+          );
+        }
+      }
+    } else {
+      final long time = timeSelector.getLong();
       final long firstTime = buf.getLong(position);
-      if (inPair.lhs < firstTime) {
-        StringFirstLastUtils.writePair(
-            buf,
-            position,
-            new SerializablePairLongString(inPair.lhs, inPair.rhs),
-            maxStringBytes
-        );
+
+      if (time < firstTime) {
+        final String value = DimensionHandlerUtils.convertObjectToString(valueSelector.getObject());
+
+        if (value != null) {
+          StringFirstLastUtils.writePair(
+              buf,
+              position,
+              new SerializablePairLongString(time, value),
+              maxStringBytes
+          );
+        }
       }
     }
   }

processing/src/main/java/org/apache/druid/query/aggregation/first/StringFirstLastUtils.java

@@ -24,6 +24,9 @@
 import org.apache.druid.segment.BaseLongColumnValueSelector;
 import org.apache.druid.segment.BaseObjectColumnValueSelector;
 import org.apache.druid.segment.DimensionHandlerUtils;
+import org.apache.druid.segment.NilColumnValueSelector;
+import org.apache.druid.segment.column.ColumnCapabilities;
+import org.apache.druid.segment.column.ValueType;
 
 import javax.annotation.Nullable;
 import java.nio.ByteBuffer;
@@ -32,10 +35,34 @@ public class StringFirstLastUtils
 {
   private static final int NULL_VALUE = -1;
 
+  /**
+   * Returns whether a given value selector *might* contain SerializablePairLongString objects.
+   */
+  public static boolean selectorNeedsFoldCheck(
+      final BaseObjectColumnValueSelector<?> valueSelector,
+      @Nullable final ColumnCapabilities valueSelectorCapabilities
+  )
+  {
+    if (valueSelectorCapabilities != null && valueSelectorCapabilities.getType() != ValueType.COMPLEX) {
+      // Known, non-complex type.
+      return false;
+    }
+
+    if (valueSelector instanceof NilColumnValueSelector) {
+      // Nil column, definitely no SerializablePairLongStrings.
+      return false;
+    }
+
+    // Check if the selector class could possibly be a SerializablePairLongString (either a superclass or subclass).
+    final Class<?> clazz = valueSelector.classOfObject();
+    return clazz.isAssignableFrom(SerializablePairLongString.class)
+           || SerializablePairLongString.class.isAssignableFrom(clazz);
+  }
+
   @Nullable
   public static SerializablePairLongString readPairFromSelectors(
       final BaseLongColumnValueSelector timeSelector,
-      final BaseObjectColumnValueSelector valueSelector
+      final BaseObjectColumnValueSelector<?> valueSelector
   )
   {
     final long time;

processing/src/main/java/org/apache/druid/query/aggregation/last/StringLastAggregator.java

@@ -26,25 +26,29 @@
 import org.apache.druid.query.aggregation.first.StringFirstLastUtils;
 import org.apache.druid.segment.BaseLongColumnValueSelector;
 import org.apache.druid.segment.BaseObjectColumnValueSelector;
+import org.apache.druid.segment.DimensionHandlerUtils;
 
 public class StringLastAggregator implements Aggregator
 {
   private final BaseLongColumnValueSelector timeSelector;
-  private final BaseObjectColumnValueSelector valueSelector;
+  private final BaseObjectColumnValueSelector<?> valueSelector;
   private final int maxStringBytes;
+  private final boolean needsFoldCheck;
 
   protected long lastTime;
   protected String lastValue;
 
   public StringLastAggregator(
-      BaseLongColumnValueSelector timeSelector,
-      BaseObjectColumnValueSelector valueSelector,
-      int maxStringBytes
+      final BaseLongColumnValueSelector timeSelector,
+      final BaseObjectColumnValueSelector<?> valueSelector,
+      final int maxStringBytes,
+      final boolean needsFoldCheck
   )
   {
     this.valueSelector = valueSelector;
     this.timeSelector = timeSelector;
     this.maxStringBytes = maxStringBytes;
+    this.needsFoldCheck = needsFoldCheck;
 
     lastTime = DateTimes.MIN.getMillis();
     lastValue = null;
@@ -53,22 +57,28 @@ public StringLastAggregator(
   @Override
   public void aggregate()
   {
-    final SerializablePairLongString inPair = StringFirstLastUtils.readPairFromSelectors(
-        timeSelector,
-        valueSelector
-    );
+    if (needsFoldCheck) {
+      // Less efficient code path when folding is a possibility (we must read the value selector first just in case
+      // it's a foldable object).
+      final SerializablePairLongString inPair = StringFirstLastUtils.readPairFromSelectors(
+          timeSelector,
+          valueSelector
+      );
 
-    if (inPair == null) {
-      // Don't aggregate nulls.
-      return;
-    }
+      if (inPair != null && inPair.rhs != null && inPair.lhs >= lastTime) {
+        lastTime = inPair.lhs;
+        lastValue = StringUtils.fastLooseChop(inPair.rhs, maxStringBytes);
+      }
+    } else {
+      final long time = timeSelector.getLong();
 
-    if (inPair != null && inPair.rhs != null && inPair.lhs >= lastTime) {
-      lastTime = inPair.lhs;
-      lastValue = inPair.rhs;
+      if (time >= lastTime) {
+        final String value = DimensionHandlerUtils.convertObjectToString(valueSelector.getObject());
 
-      if (lastValue.length() > maxStringBytes) {
-        lastValue = lastValue.substring(0, maxStringBytes);
+        if (value != null) {
+          lastTime = time;
+          lastValue = StringUtils.fastLooseChop(value, maxStringBytes);
+        }
       }
     }
   }