Ensure ordinal builder emit ordinal blocks (#127949)

docs/changelog/127949.yaml

@@ -0,0 +1,5 @@
+pr: 127949
+summary: Ensure ordinal builder emit ordinal blocks
+area: ES|QL
+type: bug
+issues: []

x-pack/plugin/esql/compute/src/main/java/org/elasticsearch/compute/data/OrdinalBytesRefBlock.java

@@ -54,7 +54,11 @@ void writeOrdinalBlock(StreamOutput out) throws IOException {
      * Returns true if this ordinal block is dense enough to enable optimizations using its ordinals
      */
     public boolean isDense() {
-        return ordinals.getTotalValueCount() * 2 / 3 >= bytes.getPositionCount();
+        return isDense(ordinals.getTotalValueCount(), bytes.getPositionCount());
+    }
+
+    public static boolean isDense(long totalPositions, long dictionarySize) {
+        return totalPositions >= 10 && totalPositions >= dictionarySize * 2L;
     }
 
     public IntBlock getOrdinalsBlock() {
@@ -251,4 +255,17 @@ public long ramBytesUsed() {
     public String toString() {
         return getClass().getSimpleName() + "[ordinals=" + ordinals + ", bytes=" + bytes + "]";
     }
+
+    @Override
+    public boolean equals(Object o) {
+        if (o instanceof BytesRefBlock that) {
+            return BytesRefBlock.equals(this, that);
+        }
+        return false;
+    }
+
+    @Override
+    public int hashCode() {
+        return BytesRefBlock.hash(this);
+    }
 }

x-pack/plugin/esql/compute/src/main/java/org/elasticsearch/compute/data/SingletonOrdinalsBuilder.java

@@ -22,6 +22,8 @@
 public class SingletonOrdinalsBuilder implements BlockLoader.SingletonOrdinalsBuilder, Releasable, Block.Builder {
     private final BlockFactory blockFactory;
     private final SortedDocValues docValues;
+    private int minOrd = Integer.MAX_VALUE;
+    private int maxOrd = Integer.MIN_VALUE;
     private final int[] ords;
     private int count;
 
@@ -39,8 +41,10 @@ public SingletonOrdinalsBuilder appendNull() {
     }
 
     @Override
-    public SingletonOrdinalsBuilder appendOrd(int value) {
-        ords[count++] = value;
+    public SingletonOrdinalsBuilder appendOrd(int ord) {
+        ords[count++] = ord;
+        minOrd = Math.min(minOrd, ord);
+        maxOrd = Math.max(maxOrd, ord);
         return this;
     }
 
@@ -55,7 +59,7 @@ public SingletonOrdinalsBuilder endPositionEntry() {
     }
 
     BytesRefBlock buildOrdinal() {
-        int valueCount = docValues.getValueCount();
+        int valueCount = maxOrd - minOrd + 1;
         long breakerSize = ordsSize(valueCount);
         blockFactory.adjustBreaker(breakerSize);
         BytesRefVector bytesVector = null;
@@ -65,7 +69,7 @@ BytesRefBlock buildOrdinal() {
             Arrays.fill(newOrds, -1);
             for (int ord : ords) {
                 if (ord != -1) {
-                    newOrds[ord] = 0;
+                    newOrds[ord - minOrd] = 0;
                 }
             }
             // resolve the ordinals and remaps the ordinals
@@ -74,7 +78,7 @@ BytesRefBlock buildOrdinal() {
                 for (int i = 0; i < newOrds.length; i++) {
                     if (newOrds[i] != -1) {
                         newOrds[i] = ++nextOrd;
-                        bytesBuilder.appendBytesRef(docValues.lookupOrd(i));
+                        bytesBuilder.appendBytesRef(docValues.lookupOrd(i + minOrd));
                     }
                 }
                 bytesVector = bytesBuilder.build();
@@ -86,7 +90,7 @@ BytesRefBlock buildOrdinal() {
                     if (ord == -1) {
                         ordinalsBuilder.appendNull();
                     } else {
-                        ordinalsBuilder.appendInt(newOrds[ord]);
+                        ordinalsBuilder.appendInt(newOrds[ord - minOrd]);
                     }
                 }
                 ordinalBlock = ordinalsBuilder.build();
@@ -107,7 +111,6 @@ BytesRefBlock buildRegularBlock() {
             blockFactory.adjustBreaker(breakerSize);
             try {
                 int[] sortedOrds = ords.clone();
-                Arrays.sort(sortedOrds);
                 int uniqueCount = compactToUnique(sortedOrds);
 
                 try (BreakingBytesRefBuilder copies = new BreakingBytesRefBuilder(blockFactory.breaker(), "ords")) {
@@ -167,7 +170,12 @@ public BytesRefBlock build() {
     }
 
     boolean shouldBuildOrdinalsBlock() {
-        return ords.length >= 2 * docValues.getValueCount() && ords.length >= 32;
+        if (minOrd <= maxOrd) {
+            int numOrds = maxOrd - minOrd + 1;
+            return OrdinalBytesRefBlock.isDense(ords.length, numOrds);
+        } else {
+            return false;
+        }
     }
 
     @Override

x-pack/plugin/esql/compute/src/test/java/org/elasticsearch/compute/data/SingletonOrdinalsBuilderTests.java

@@ -8,7 +8,10 @@
 package org.elasticsearch.compute.data;
 
 import org.apache.lucene.document.SortedDocValuesField;
+import org.apache.lucene.index.DirectoryReader;
 import org.apache.lucene.index.IndexReader;
+import org.apache.lucene.index.IndexWriter;
+import org.apache.lucene.index.IndexWriterConfig;
 import org.apache.lucene.index.LeafReaderContext;
 import org.apache.lucene.index.SortedDocValues;
 import org.apache.lucene.store.Directory;
@@ -37,6 +40,7 @@
 import static org.elasticsearch.test.MapMatcher.assertMap;
 import static org.elasticsearch.test.MapMatcher.matchesMap;
 import static org.hamcrest.Matchers.equalTo;
+import static org.hamcrest.Matchers.hasSize;
 
 public class SingletonOrdinalsBuilderTests extends ESTestCase {
     public void testReader() throws IOException {
@@ -154,6 +158,39 @@ public void testAllNull() throws IOException {
         }
     }
 
+    public void testEmitOrdinalForHighCardinality() throws IOException {
+        BlockFactory factory = breakingDriverContext().blockFactory();
+        int numOrds = between(50, 100);
+        try (Directory directory = newDirectory(); IndexWriter indexWriter = new IndexWriter(directory, new IndexWriterConfig())) {
+            for (int o = 0; o < numOrds; o++) {
+                int docPerOrds = between(10, 15);
+                for (int d = 0; d < docPerOrds; d++) {
+                    indexWriter.addDocument(List.of(new SortedDocValuesField("f", new BytesRef("value-" + o))));
+                }
+            }
+            try (IndexReader reader = DirectoryReader.open(indexWriter)) {
+                assertThat(reader.leaves(), hasSize(1));
+                for (LeafReaderContext ctx : reader.leaves()) {
+                    int batchSize = between(40, 100);
+                    int ord = random().nextInt(numOrds);
+                    try (
+                        var b1 = new SingletonOrdinalsBuilder(factory, ctx.reader().getSortedDocValues("f"), batchSize);
+                        var b2 = new SingletonOrdinalsBuilder(factory, ctx.reader().getSortedDocValues("f"), batchSize)
+                    ) {
+                        for (int i = 0; i < batchSize; i++) {
+                            b1.appendOrd(ord);
+                            b2.appendOrd(ord);
+                        }
+                        try (BytesRefBlock block1 = b1.build(); BytesRefBlock block2 = b2.buildRegularBlock()) {
+                            assertThat(block1, equalTo(block2));
+                            assertNotNull(block1.asOrdinals());
+                        }
+                    }
+                }
+            }
+        }
+    }
+
     static BytesRefBlock buildOrdinalsBuilder(SingletonOrdinalsBuilder builder) {
         if (randomBoolean()) {
             return builder.buildRegularBlock();