googleapis
diff --git a/‎README.md‎
Lines changed: 1 addition & 1 deletion b/‎README.md‎
Lines changed: 1 addition & 1 deletion
diff --git a/‎google-cloud-bigquerystorage/src/main/java/com/google/cloud/bigquery/storage/v1/ConnectionWorkerPool.java‎
Lines changed: 183 additions & 2 deletions b/‎google-cloud-bigquerystorage/src/main/java/com/google/cloud/bigquery/storage/v1/ConnectionWorkerPool.java‎
Lines changed: 183 additions & 2 deletions
diff --git a/‎google-cloud-bigquerystorage/src/main/java/com/google/cloud/bigquery/storage/v1/StreamWriter.java‎
Lines changed: 5 additions & 0 deletions b/‎google-cloud-bigquerystorage/src/main/java/com/google/cloud/bigquery/storage/v1/StreamWriter.java‎
Lines changed: 5 additions & 0 deletions
@@ -49,7 +49,7 @@ If you are using Maven without BOM, add this to your dependencies:
 If you are using Gradle 5.x or later, add this to your dependencies:
 
 ```Groovy
-implementation platform('com.google.cloud:libraries-bom:26.1.1')
+implementation platform('com.google.cloud:libraries-bom:26.1.2')
 
 implementation 'com.google.cloud:google-cloud-bigquerystorage'
 ```
 
@@ -18,9 +18,26 @@
 import com.google.api.core.ApiFuture;
 import com.google.api.gax.batching.FlowController;
 import com.google.auto.value.AutoValue;
+import com.google.cloud.bigquery.storage.v1.ConnectionWorker.Load;
+import com.google.common.base.Stopwatch;
+import com.google.common.collect.ImmutableList;
+import java.io.IOException;
+import java.util.Collections;
+import java.util.Comparator;
+import java.util.HashSet;
+import java.util.List;
+import java.util.Map;
+import java.util.Set;
+import java.util.concurrent.ConcurrentHashMap;
+import java.util.concurrent.atomic.AtomicInteger;
+import java.util.concurrent.locks.Lock;
+import java.util.concurrent.locks.ReentrantLock;
+import java.util.logging.Logger;
 import javax.annotation.concurrent.GuardedBy;
 
+/** Pool of connections to accept appends and distirbute to different connections. */
 public class ConnectionWorkerPool {
+  private static final Logger log = Logger.getLogger(ConnectionWorkerPool.class.getName());
   /*
    * Max allowed inflight requests in the stream. Method append is blocked at this.
    */
@@ -36,11 +53,29 @@ public class ConnectionWorkerPool {
    */
   private final FlowController.LimitExceededBehavior limitExceededBehavior;
 
+  /** Map from write stream to corresponding connection. */
+  private final Map<StreamWriter, ConnectionWorker> streamWriterToConnection =
+      new ConcurrentHashMap<>();
+
+  /** Map from a connection to a set of write stream that have sent requests onto it. */
+  private final Map<ConnectionWorker, Set<StreamWriter>> connectionToWriteStream =
+      new ConcurrentHashMap<>();
+
+  /** Collection of all the created connections. */
+  private final Set<ConnectionWorker> connectionWorkerPool =
+      Collections.synchronizedSet(new HashSet<>());
+
+  /** Enable test related logic. */
+  private static boolean enableTesting = false;
+
   /*
    * TraceId for debugging purpose.
    */
   private final String traceId;
 
+  /** Used for test on the number of times createWorker is called. */
+  private final AtomicInteger testValueCreateConnectionCount = new AtomicInteger(0);
+
   /*
    * Tracks current inflight requests in the stream.
    */
@@ -102,6 +137,15 @@ public class ConnectionWorkerPool {
    */
   private boolean ownsBigQueryWriteClient = false;
 
+  /**
+   * The current maximum connection count. This value is gradually increased till the user defined
+   * maximum connection count.
+   */
+  private int currentMaxConnectionCount;
+
+  /** Lock for controlling concurrent operation on add / delete connections. */
+  private final Lock lock = new ReentrantLock();
+
   /** Settings for connection pool. */
   @AutoValue
   public abstract static class Settings {
@@ -147,6 +191,7 @@ public ConnectionWorkerPool(
     this.traceId = traceId;
     this.client = client;
     this.ownsBigQueryWriteClient = ownsBigQueryWriteClient;
+    this.currentMaxConnectionCount = settings.minConnectionsPerPool();
   }
 
   /**
@@ -160,13 +205,149 @@ public static void setOptions(Settings settings) {
 
   /** Distributes the writing of a message to an underlying connection. */
   public ApiFuture<AppendRowsResponse> append(StreamWriter streamWriter, ProtoRows rows) {
-    throw new RuntimeException("Append is not implemented!");
+    return append(streamWriter, rows, -1);
   }
 
   /** Distributes the writing of a message to an underlying connection. */
   public ApiFuture<AppendRowsResponse> append(
       StreamWriter streamWriter, ProtoRows rows, long offset) {
-    throw new RuntimeException("append with offset is not implemented on connection pool!");
+    // We are in multiplexing mode after entering the following logic.
+    ConnectionWorker connectionWorker =
+        streamWriterToConnection.compute(
+            streamWriter,
+            (key, existingStream) -> {
+              // Though compute on concurrent map is atomic, we still do explicit locking as we
+              // may have concurrent close(...) triggered.
+              lock.lock();
+              try {
+                // Stick to the existing stream if it's not overwhelmed.
+                if (existingStream != null && !existingStream.getLoad().isOverwhelmed()) {
+                  return existingStream;
+                }
+                // Try to create or find another existing stream to reuse.
+                ConnectionWorker createdOrExistingConnection = null;
+                try {
+                  createdOrExistingConnection =
+                      createOrReuseConnectionWorker(streamWriter, existingStream);
+                } catch (IOException e) {
+                  throw new IllegalStateException(e);
+                }
+                // Update connection to write stream relationship.
+                connectionToWriteStream.computeIfAbsent(
+                    createdOrExistingConnection, (ConnectionWorker k) -> new HashSet<>());
+                connectionToWriteStream.get(createdOrExistingConnection).add(streamWriter);
+                return createdOrExistingConnection;
+              } finally {
+                lock.unlock();
+              }
+            });
+    Stopwatch stopwatch = Stopwatch.createStarted();
+    ApiFuture<AppendRowsResponse> responseFuture =
+        connectionWorker.append(
+            streamWriter.getStreamName(), streamWriter.getProtoSchema(), rows, offset);
+    return responseFuture;
+  }
+
+  /**
+   * Create a new connection if we haven't reached current maximum, or reuse an existing connection
+   * with least load.
+   */
+  private ConnectionWorker createOrReuseConnectionWorker(
+      StreamWriter streamWriter, ConnectionWorker existingConnectionWorker) throws IOException {
+    String streamReference = streamWriter.getStreamName();
+    if (connectionWorkerPool.size() < currentMaxConnectionCount) {
+      // Always create a new connection if we haven't reached current maximum.
+      return createConnectionWorker(streamWriter.getStreamName(), streamWriter.getProtoSchema());
+    } else {
+      ConnectionWorker existingBestConnection =
+          pickBestLoadConnection(
+              enableTesting ? Load.TEST_LOAD_COMPARATOR : Load.LOAD_COMPARATOR,
+              ImmutableList.copyOf(connectionWorkerPool));
+      if (!existingBestConnection.getLoad().isOverwhelmed()) {
+        return existingBestConnection;
+      } else if (currentMaxConnectionCount < settings.maxConnectionsPerPool()) {
+        // At this point, we have reached the connection cap and the selected connection is
+        // overwhelmed, we can try scale up the connection pool.
+        // The connection count will go up one by one until `maxConnectionsPerPool` is reached.
+        currentMaxConnectionCount += 1;
+        if (currentMaxConnectionCount > settings.maxConnectionsPerPool()) {
+          currentMaxConnectionCount = settings.maxConnectionsPerPool();
+        }
+        return createConnectionWorker(streamWriter.getStreamName(), streamWriter.getProtoSchema());
+      } else {
+        // Stick to the original connection if all the connections are overwhelmed.
+        if (existingConnectionWorker != null) {
+          return existingConnectionWorker;
+        }
+        // If we are at this branch, it means we reached the maximum connections.
+        return existingBestConnection;
+      }
+    }
+  }
+
+  /** Select out the best connection worker among the given connection workers. */
+  static ConnectionWorker pickBestLoadConnection(
+      Comparator<Load> comparator, List<ConnectionWorker> connectionWorkerList) {
+    if (connectionWorkerList.isEmpty()) {
+      throw new IllegalStateException(
+          String.format(
+              "Bug in code! At least one connection worker should be passed in "
+                  + "pickSemiBestLoadConnection(...)"));
+    }
+    // Compare all connection workers to find the connection worker with the smallest load.
+    // Loop and find the connection with the least load.
+    // The load comparision and computation process
+    int currentBestIndex = 0;
+    Load currentBestLoad = connectionWorkerList.get(currentBestIndex).getLoad();
+    for (int i = 1; i < connectionWorkerList.size(); i++) {
+      Load loadToCompare = connectionWorkerList.get(i).getLoad();
+      if (comparator.compare(loadToCompare, currentBestLoad) <= 0) {
+        currentBestIndex = i;
+        currentBestLoad = loadToCompare;
+      }
+    }
+    return connectionWorkerList.get(currentBestIndex);
+  }
+
+  /**
+   * Creates a single connection worker.
+   *
+   * <p>Note this function need to be thread-safe across different stream reference but no need for
+   * a single stream reference. This is because createConnectionWorker(...) is called via
+   * computeIfAbsent(...) which is at most once per key.
+   */
+  private ConnectionWorker createConnectionWorker(String streamName, ProtoSchema writeSchema)
+      throws IOException {
+    if (enableTesting) {
+      // Though atomic integer is super lightweight, add extra if check in case adding future logic.
+      testValueCreateConnectionCount.getAndIncrement();
+    }
+    ConnectionWorker connectionWorker =
+        new ConnectionWorker(
+            streamName,
+            writeSchema,
+            maxInflightRequests,
+            maxInflightBytes,
+            limitExceededBehavior,
+            traceId,
+            client,
+            ownsBigQueryWriteClient);
+    connectionWorkerPool.add(connectionWorker);
+    log.info(
+        String.format(
+            "Scaling up new connection for stream name: %s, pool size after scaling up %s",
+            streamName, connectionWorkerPool.size()));
+    return connectionWorker;
+  }
+
+  /** Enable Test related logic. */
+  public static void enableTestingLogic() {
+    enableTesting = true;
+  }
+
+  /** Returns how many times createConnectionWorker(...) is called. */
+  int getCreateConnectionCount() {
+    return testValueCreateConnectionCount.get();
   }
 
   /** Close the stream writer. Shut down all resources. */
 
@@ -152,6 +152,11 @@ public String getStreamName() {
     return streamName;
   }
 
+  /** @return the passed in user schema. */
+  public ProtoSchema getProtoSchema() {
+    return writerSchema;
+  }
+
   /** Close the stream writer. Shut down all resources. */
   @Override
   public void close() {