Remove page alignment in exchange sink (elastic#124610)

I see that planning the ExchangeSinkExec takes a few milliseconds when 
benchmarking simple queries with 10K fields. It spends time checking if
we need to realign the incoming pages. However, the exchange has the
exact same attributes as its child, so the incoming layout should match
its attributes perfectly. This change removes the realignment.

Author: dnhatn

docs/changelog/124610.yaml

@@ -0,0 +1,5 @@
+pr: 124610
+summary: Remove page alignment in exchange sink
+area: ES|QL
+type: enhancement
+issues: []

x-pack/plugin/esql/compute/src/main/java/org/elasticsearch/compute/operator/exchange/ExchangeSinkOperator.java

@@ -23,7 +23,6 @@
 
 import java.io.IOException;
 import java.util.Objects;
-import java.util.function.Function;
 import java.util.function.Supplier;
 
 /**
@@ -32,17 +31,14 @@
 public class ExchangeSinkOperator extends SinkOperator {
 
     private final ExchangeSink sink;
-    private final Function<Page, Page> transformer;
     private int pagesReceived;
     private long rowsReceived;
 
-    public record ExchangeSinkOperatorFactory(Supplier<ExchangeSink> exchangeSinks, Function<Page, Page> transformer)
-        implements
-            SinkOperatorFactory {
+    public record ExchangeSinkOperatorFactory(Supplier<ExchangeSink> exchangeSinks) implements SinkOperatorFactory {
 
         @Override
         public SinkOperator get(DriverContext driverContext) {
-            return new ExchangeSinkOperator(exchangeSinks.get(), transformer);
+            return new ExchangeSinkOperator(exchangeSinks.get());
         }
 
         @Override
@@ -51,9 +47,8 @@ public String describe() {
         }
     }
 
-    public ExchangeSinkOperator(ExchangeSink sink, Function<Page, Page> transformer) {
+    public ExchangeSinkOperator(ExchangeSink sink) {
         this.sink = sink;
-        this.transformer = transformer;
     }
 
     @Override
@@ -84,7 +79,7 @@ public boolean needsInput() {
     protected void doAddInput(Page page) {
         pagesReceived++;
         rowsReceived += page.getPositionCount();
-        sink.addPage(transformer.apply(page));
+        sink.addPage(page);
     }
 
     @Override

x-pack/plugin/esql/compute/src/test/java/org/elasticsearch/compute/operator/DriverTests.java

@@ -45,7 +45,6 @@
 import java.util.concurrent.CyclicBarrier;
 import java.util.concurrent.TimeUnit;
 import java.util.concurrent.atomic.AtomicInteger;
-import java.util.function.Function;
 import java.util.function.LongSupplier;
 
 import static org.hamcrest.Matchers.either;
@@ -328,7 +327,7 @@ public void testEarlyTermination() {
             final int maxAllowedRows = between(1, 100);
             final AtomicInteger processedRows = new AtomicInteger(0);
             var sinkHandler = new ExchangeSinkHandler(driverContext.blockFactory(), positions, System::currentTimeMillis);
-            var sinkOperator = new ExchangeSinkOperator(sinkHandler.createExchangeSink(() -> {}), Function.identity());
+            var sinkOperator = new ExchangeSinkOperator(sinkHandler.createExchangeSink(() -> {}));
             final var delayOperator = new EvalOperator(driverContext.blockFactory(), new EvalOperator.ExpressionEvaluator() {
                 @Override
                 public Block eval(Page page) {
@@ -365,7 +364,7 @@ public void testResumeOnEarlyFinish() throws Exception {
             var sourceHandler = new ExchangeSourceHandler(between(1, 5), threadPool.executor("esql"));
             var sinkHandler = new ExchangeSinkHandler(driverContext.blockFactory(), between(1, 5), System::currentTimeMillis);
             var sourceOperator = new ExchangeSourceOperator(sourceHandler.createExchangeSource());
-            var sinkOperator = new ExchangeSinkOperator(sinkHandler.createExchangeSink(() -> {}), Function.identity());
+            var sinkOperator = new ExchangeSinkOperator(sinkHandler.createExchangeSink(() -> {}));
             Driver driver = TestDriverFactory.create(driverContext, sourceOperator, List.of(), sinkOperator);
             PlainActionFuture<Void> future = new PlainActionFuture<>();
             Driver.start(threadPool.getThreadContext(), threadPool.executor("esql"), driver, between(1, 1000), future);

x-pack/plugin/esql/compute/src/test/java/org/elasticsearch/compute/operator/ForkingOperatorTestCase.java

@@ -39,7 +39,6 @@
 import java.util.Iterator;
 import java.util.List;
 import java.util.Set;
-import java.util.function.Function;
 import java.util.stream.Collectors;
 import java.util.stream.IntStream;
 import java.util.stream.Stream;
@@ -242,7 +241,7 @@ List<Driver> createDriversForInput(List<Page> input, List<Page> results, boolean
                         simpleWithMode(AggregatorMode.INTERMEDIATE).get(driver1Context),
                         intermediateOperatorItr.next()
                     ),
-                    new ExchangeSinkOperator(sinkExchanger.createExchangeSink(() -> {}), Function.identity())
+                    new ExchangeSinkOperator(sinkExchanger.createExchangeSink(() -> {}))
                 )
             );
         }

x-pack/plugin/esql/compute/src/test/java/org/elasticsearch/compute/operator/exchange/ExchangeServiceTests.java

@@ -65,7 +65,6 @@
 import java.util.concurrent.TimeUnit;
 import java.util.concurrent.atomic.AtomicBoolean;
 import java.util.concurrent.atomic.AtomicInteger;
-import java.util.function.Function;
 import java.util.function.Supplier;
 import java.util.stream.Collectors;
 import java.util.stream.IntStream;
@@ -305,7 +304,7 @@ Set<Integer> runConcurrentTest(
                 "sink-" + i,
                 dc,
                 seqNoGenerator.get(dc),
-                new ExchangeSinkOperator(exchangeSink.get(), Function.identity())
+                new ExchangeSinkOperator(exchangeSink.get())
             );
             drivers.add(d);
         }

x-pack/plugin/esql/src/main/java/org/elasticsearch/xpack/esql/plan/physical/ExchangeSinkExec.java

@@ -27,6 +27,7 @@ public class ExchangeSinkExec extends UnaryExec {
     );
 
     private final List<Attribute> output;
+    // TODO: remove this flag
     private final boolean intermediateAgg;
 
     public ExchangeSinkExec(Source source, List<Attribute> output, boolean intermediateAgg, PhysicalPlan child) {

x-pack/plugin/esql/src/main/java/org/elasticsearch/xpack/esql/planner/LocalExecutionPlanner.java

@@ -385,14 +385,8 @@ private PhysicalOperation planExchange(ExchangeExec exchangeExec, LocalExecution
     private PhysicalOperation planExchangeSink(ExchangeSinkExec exchangeSink, LocalExecutionPlannerContext context) {
         Objects.requireNonNull(exchangeSinkSupplier, "ExchangeSinkHandler wasn't provided");
         var child = exchangeSink.child();
-
         PhysicalOperation source = plan(child, context);
-
-        Function<Page, Page> transformer = exchangeSink.isIntermediateAgg()
-            ? Function.identity()
-            : alignPageToAttributes(exchangeSink.output(), source.layout);
-
-        return source.withSink(new ExchangeSinkOperatorFactory(exchangeSinkSupplier, transformer), source.layout);
+        return source.withSink(new ExchangeSinkOperatorFactory(exchangeSinkSupplier), source.layout);
     }
 
     private PhysicalOperation planExchangeSource(ExchangeSourceExec exchangeSource, LocalExecutionPlannerContext context) {