Avoid expensive status update in LuceneOperator (#134079)

With doc_partitioning targeting large shards, updating the status of 
LuceneOperator can be expensive with many slices. This change uses the
keys of the partitioning map instead of iterating over all slices in the
queue.

Author: dnhatn

x-pack/plugin/esql/compute/src/main/java/org/elasticsearch/compute/lucene/LuceneOperator.java

@@ -33,7 +33,6 @@
 
 import java.io.IOException;
 import java.io.UncheckedIOException;
-import java.util.Collection;
 import java.util.Collections;
 import java.util.HashSet;
 import java.util.List;
@@ -284,20 +283,14 @@ List<Object> tags() {
     public String toString() {
         StringBuilder sb = new StringBuilder();
         sb.append(this.getClass().getSimpleName()).append("[");
-        sb.append("shards = ").append(sortedUnion(processedShards, sliceQueue.remainingShardsIdentifiers()));
+        sb.append("shards = ")
+            .append(sliceQueue.partitioningStrategies().keySet().stream().sorted().collect(Collectors.joining(",", "[", "]")));
         sb.append(", maxPageSize = ").append(maxPageSize);
         describe(sb);
         sb.append("]");
         return sb.toString();
     }
 
-    private static Set<String> sortedUnion(Collection<String> a, Collection<String> b) {
-        var result = new TreeSet<String>();
-        result.addAll(a);
-        result.addAll(b);
-        return result;
-    }
-
     protected abstract void describe(StringBuilder sb);
 
     @Override

x-pack/plugin/esql/compute/src/main/java/org/elasticsearch/compute/lucene/LuceneSliceQueue.java

@@ -23,7 +23,6 @@
 import java.io.UncheckedIOException;
 import java.util.ArrayList;
 import java.util.Arrays;
-import java.util.Collection;
 import java.util.Collections;
 import java.util.Comparator;
 import java.util.HashMap;
@@ -178,17 +177,6 @@ public Map<String, PartitioningStrategy> partitioningStrategies() {
         return partitioningStrategies;
     }
 
-    public Collection<String> remainingShardsIdentifiers() {
-        List<String> remaining = new ArrayList<>(slices.length());
-        for (int i = 0; i < slices.length(); i++) {
-            LuceneSlice slice = slices.get(i);
-            if (slice != null) {
-                remaining.add(slice.shardContext().shardIdentifier());
-            }
-        }
-        return remaining;
-    }
-
     public static LuceneSliceQueue create(
         List<? extends ShardContext> contexts,
         Function<ShardContext, List<QueryAndTags>> queryFunction,