separate the logic in ManageWorkerPool

src/backend/distributed/executor/adaptive_executor.c

@@ -590,6 +590,11 @@ static WorkerSession * FindOrCreateWorkerSession(WorkerPool *workerPool,
 												 MultiConnection *connection);
 static void ManageWorkerPool(WorkerPool *workerPool);
 static bool ShouldWaitForConnection(WorkerPool *workerPool);
+static bool CanOpenNewConnection(WorkerPool *workerPool);
+static bool IsTooEarlyToOpenConnections(WorkerPool *workerPool);
+static int CalculateNewConnectionCount(WorkerPool *workerPool);
+static void OpenNewConnections(WorkerPool *workerPool, int newConnectionCount,
+							   TransactionProperties *transactionProperties);
 static void CheckConnectionTimeout(WorkerPool *workerPool);
 static int UsableConnectionCount(WorkerPool *workerPool);
 static long NextEventTimeout(DistributedExecution *execution);
@@ -2300,29 +2305,39 @@ static void
 ManageWorkerPool(WorkerPool *workerPool)
 {
 	DistributedExecution *execution = workerPool->distributedExecution;
-	int targetPoolSize = execution->targetPoolSize;
+
-	int initiatedConnectionCount = list_length(workerPool->sessionList);
+	if (!CanOpenNewConnection(workerPool))
-	int activeConnectionCount PG_USED_FOR_ASSERTS_ONLY =
+	{
-		workerPool->activeConnectionCount;
+		return;
-	int idleConnectionCount PG_USED_FOR_ASSERTS_ONLY =
+	}
-		workerPool->idleConnectionCount;
+
+	int newConnectionCount = CalculateNewConnectionCount(workerPool);
+
+	if (newConnectionCount <= 0)
+	{
+		return;
+	}
+
+	OpenNewConnections(workerPool, newConnectionCount, execution->transactionProperties);
+
+	INSTR_TIME_SET_CURRENT(workerPool->lastConnectionOpenTime);
+	execution->connectionSetChanged = true;
+}
+
+
+/*
+ * CanOpenNewConnection returns true if we can open new connections
+ * for the given workerPool.
+ */
+static bool
+CanOpenNewConnection(WorkerPool *workerPool)
+{
 	int failedConnectionCount = workerPool->failedConnectionCount;
-	int readyTaskCount = workerPool->readyTaskCount;
-	int newConnectionCount = 0;
-
-	/* we should always have more (or equal) active connections than idle connections */
-	Assert(activeConnectionCount >= idleConnectionCount);
-
-	/* we should always have more (or equal) initiated connections than active connections */
-	Assert(initiatedConnectionCount >= activeConnectionCount);
-
-	/* we should never have less than 0 connections ever */
-	Assert(activeConnectionCount >= 0 && idleConnectionCount >= 0);
 
 	if (workerPool->failed)
 	{
 		/* connection pool failed */
-		return;
+		return false;
 	}
 
 	/* we might fail the execution or warn the user about connection timeouts */
@@ -2334,9 +2349,60 @@ ManageWorkerPool(WorkerPool *workerPool)
 	if (failedConnectionCount >= 1)
 	{
 		/* do not attempt to open more connections after one failed */
-		return;
+		return false;
 	}
 
+	if (IsTooEarlyToOpenConnections(workerPool))
+	{
+		return false;
+	}
+
+	return true;
+}
+
+
+/*
+ * IsTooEarlyToOpenConnections returns true if we should not open
+ * new connections.
+ */
+static bool
+IsTooEarlyToOpenConnections(WorkerPool *workerPool)
+{
+	return !UseConnectionPerPlacement() && ExecutorSlowStartInterval !=
+		   SLOW_START_DISABLED &&
+		   (MillisecondsPassedSince(workerPool->lastConnectionOpenTime) <
+			ExecutorSlowStartInterval);
+}
+
+
+/*
+ * CalculateNewConnectionCount returns the amount of connections
+ * that we can currently open.
+ */
+static int
+CalculateNewConnectionCount(WorkerPool *workerPool)
+{
+	DistributedExecution *execution = workerPool->distributedExecution;
+
+	int targetPoolSize = execution->targetPoolSize;
+	int initiatedConnectionCount = list_length(workerPool->sessionList);
+	int activeConnectionCount PG_USED_FOR_ASSERTS_ONLY =
+		workerPool->activeConnectionCount;
+	int idleConnectionCount PG_USED_FOR_ASSERTS_ONLY =
+		workerPool->idleConnectionCount;
+	int readyTaskCount = workerPool->readyTaskCount;
+	int newConnectionCount = 0;
+
+
+	/* we should always have more (or equal) active connections than idle connections */
+	Assert(activeConnectionCount >= idleConnectionCount);
+
+	/* we should always have more (or equal) initiated connections than active connections */
+	Assert(initiatedConnectionCount >= activeConnectionCount);
+
+	/* we should never have less than 0 connections ever */
+	Assert(activeConnectionCount >= 0 && idleConnectionCount >= 0);
+
 	if (UseConnectionPerPlacement())
 	{
 		int unusedConnectionCount = workerPool->unusedConnectionCount;
@@ -2361,7 +2427,14 @@ ManageWorkerPool(WorkerPool *workerPool)
 		 * Number of additional connections we would need to run all ready tasks in
 		 * parallel.
 		 */
-		int newConnectionsForReadyTasks = readyTaskCount - usableConnectionCount;
+		int newConnectionsForReadyTasks = Max(0, readyTaskCount - usableConnectionCount);
+
+		/* If Slow start is enabled we need to update the maxNewConnection to the current cycle's maximum.*/
+		if (ExecutorSlowStartInterval > 0)
+		{
+			maxNewConnectionCount = Min(workerPool->maxNewConnectionsPerCycle,
+										maxNewConnectionCount);
+		}
 
 		/*
 		 * Open enough connections to handle all tasks that are ready, but no more
@@ -2369,30 +2442,23 @@ ManageWorkerPool(WorkerPool *workerPool)
 		 */
 		newConnectionCount = Min(newConnectionsForReadyTasks, maxNewConnectionCount);
 
-		if (newConnectionCount > 0 && ExecutorSlowStartInterval != SLOW_START_DISABLED)
+		if (newConnectionCount > 0)
 		{
-			if (MillisecondsPassedSince(workerPool->lastConnectionOpenTime) >=
-				ExecutorSlowStartInterval)
-			{
-				newConnectionCount = Min(newConnectionCount,
-										 workerPool->maxNewConnectionsPerCycle);
-
 			/* increase the open rate every cycle (like TCP slow start) */
 			workerPool->maxNewConnectionsPerCycle += 1;
 		}
-			else
-			{
-				/* wait a bit until opening more connections */
-				return;
-			}
 	}
+	return newConnectionCount;
 }
 
-	if (newConnectionCount <= 0)
-	{
-		return;
-	}
 
+/*
+ * OpenNewConnections opens the given amount of connections for the given workerPool.
+ */
+static void
+OpenNewConnections(WorkerPool *workerPool, int newConnectionCount,
+				   TransactionProperties *transactionProperties)
+{
 	ereport(DEBUG4, (errmsg("opening %d new connections to %s:%d", newConnectionCount,
 							workerPool->nodeName, workerPool->nodePort)));
 
@@ -2401,7 +2467,7 @@ ManageWorkerPool(WorkerPool *workerPool)
 		/* experimental: just to see the perf benefits of caching connections */
 		int connectionFlags = 0;
 
-		if (execution->transactionProperties->useRemoteTransactionBlocks ==
+		if (transactionProperties->useRemoteTransactionBlocks ==
 			TRANSACTION_BLOCKS_DISALLOWED)
 		{
 			connectionFlags |= OUTSIDE_TRANSACTION;
@@ -2480,9 +2546,6 @@ ManageWorkerPool(WorkerPool *workerPool)
 		/* immediately run the state machine to handle potential failure */
 		ConnectionStateMachine(session);
 	}
-
-	INSTR_TIME_SET_CURRENT(workerPool->lastConnectionOpenTime);
-	execution->connectionSetChanged = true;
 }