(index-client) Clean up index client code

This should have the rpc stream reception be performed in parallel in separate threads, rather blocking sequentially in the main thread, hopefully giving a slight performance boost.

code/index/api/java/nu/marginalia/index/api/IndexClient.java

@@ -16,20 +16,18 @@ import org.slf4j.LoggerFactory;
 
 import java.util.ArrayList;
 import java.util.Comparator;
-import java.util.Iterator;
 import java.util.List;
 import java.util.concurrent.CompletableFuture;
 import java.util.concurrent.ExecutorService;
 import java.util.concurrent.Executors;
-
-import static java.lang.Math.clamp;
+import java.util.concurrent.atomic.AtomicInteger;
 
 @Singleton
 public class IndexClient {
     private static final Logger logger = LoggerFactory.getLogger(IndexClient.class);
     private final GrpcMultiNodeChannelPool<IndexApiGrpc.IndexApiBlockingStub> channelPool;
     private final DomainBlacklistImpl blacklist;
-    private static final ExecutorService executor = Executors.newVirtualThreadPerTaskExecutor();
+    private static final ExecutorService executor = Executors.newCachedThreadPool();
 
     @Inject
     public IndexClient(GrpcChannelPoolFactory channelPoolFactory, DomainBlacklistImpl blacklist) {
@@ -51,40 +49,31 @@ public class IndexClient {
 
     /** Execute a query on the index partitions and return the combined results. */
     public AggregateQueryResponse executeQueries(RpcIndexQuery indexRequest, Pagination pagination) {
-        List<CompletableFuture<Iterator<RpcDecoratedResultItem>>> futures =
-                channelPool.call(IndexApiGrpc.IndexApiBlockingStub::query)
-                        .async(executor)
-                        .runEach(indexRequest);
 
         final int requestedMaxResults = indexRequest.getQueryLimits().getResultsTotal();
-        final int resultsUpperBound = requestedMaxResults * channelPool.getNumNodes();
 
-        List<RpcDecoratedResultItem> results = new ArrayList<>(resultsUpperBound);
+        AtomicInteger totalNumResults = new AtomicInteger(0);
 
-        for (var future : futures) {
-            try {
-                future.get().forEachRemaining(results::add);
-            }
-            catch (Exception e) {
-                logger.error("Downstream exception", e);
-            }
-        }
+        List<RpcDecoratedResultItem> results =
+                channelPool.call(IndexApiGrpc.IndexApiBlockingStub::query)
+                        .async(executor)
+                        .runEach(indexRequest)
+                        .stream()
+                        .map(future -> future.thenApply(iterator -> {
+                            List<RpcDecoratedResultItem> ret = new ArrayList<>(requestedMaxResults);
+                            iterator.forEachRemaining(ret::add);
+                            totalNumResults.addAndGet(ret.size());
+                            return ret;
+                        }))
+                        .map(CompletableFuture::join)
+                        .flatMap(List::stream)
+                        .filter(item -> !isBlacklisted(item))
+                        .sorted(comparator)
+                        .skip(Math.max(0, (pagination.page - 1) * pagination.pageSize))
+                        .limit(pagination.pageSize)
+                        .toList();
 
-        // Sort the results by ranking score and remove blacklisted domains
-        results.sort(comparator);
-        results.removeIf(this::isBlacklisted);
-
-        int numReceivedResults = results.size();
-
-        // pagination is typically 1-indexed, so we need to adjust the start and end indices
-        int indexStart = (pagination.page - 1) * pagination.pageSize;
-        int indexEnd = (pagination.page) * pagination.pageSize;
-
-        results = results.subList(
-                clamp(indexStart, 0, Math.max(0, results.size() - 1)), // from is inclusive, so subtract 1 from size()
-                clamp(indexEnd, 0, results.size()));
-
-        return new AggregateQueryResponse(results, pagination.page(), numReceivedResults);
+        return new AggregateQueryResponse(results, pagination.page(), totalNumResults.get());
     }
 
     private boolean isBlacklisted(RpcDecoratedResultItem item) {