Some indentation/style fixes

src/backend/distributed/connection/connection_management.c

@@ -324,7 +324,7 @@ StartNodeUserDatabaseConnection(uint32 flags, const char *hostname, int32 port,
 	{
 		/*
 		 * The caller doesn't want the connection manager to wait
-		 * until a connection slot is avaliable on the remote node.
+		 * until a connection slot is available on the remote node.
 		 * In the end, we might fail to establish connection to the
 		 * remote node as it might not have any space in
 		 * max_connections for this connection establishment.
@@ -362,7 +362,7 @@ StartNodeUserDatabaseConnection(uint32 flags, const char *hostname, int32 port,
 	PG_CATCH();
 	{
 		/*
-		 * Something went wrong, make sure to decement
+		 * Something went wrong, make sure to decrement
 		 * here otherwise we'd leak the increment we have done for this
 		 * connection attempt.
 		 */

src/backend/distributed/connection/shared_connection_stats.c

@@ -37,7 +37,7 @@
 
 
 /*
- * The data structure used to store data in shared memory. This data structure only
+ * The data structure used to store data in shared memory. This data structure is only
  * used for storing the lock. The actual statistics about the connections are stored
  * in the hashmap, which is allocated separately, as Postgres provides different APIs
  * for allocating hashmaps in the shared memory.
@@ -85,7 +85,7 @@ typedef struct SharedConnStatsHashEntry
  */
 int MaxSharedPoolSize = 0;
 
-/* the following two structs used for accessing shared memory */
+/* the following two structs are used for accessing shared memory */
 static HTAB *SharedConnStatsHash = NULL;
 static ConnectionStatsSharedData *ConnectionStatsSharedState = NULL;
 
@@ -185,7 +185,7 @@ RemoveAllSharedConnectionEntriesForNode(char *hostname, int port)
 	connKey.port = port;
 	strlcpy(connKey.hostname, hostname, MAX_NODE_LENGTH);
 
-	/* we're reading all shared connections, prevent any changes */
+	/* we're modifying the hashmap, prevent any concurrent access */
 	LockConnectionSharedMemory(LW_EXCLUSIVE);
 
 	bool entryFound = false;
@@ -269,11 +269,9 @@ TryToIncrementSharedConnectionCounter(const char *hostname, int port)
 	LockConnectionSharedMemory(LW_EXCLUSIVE);
 
 	/*
-	 * Note that while holding a spinlock, it would not allowed to use HASH_ENTER_NULL
-	 * if the entries in SharedConnStatsHash were allocated via palloc (as palloc
-	 * might throw OOM errors). However, in this case we're safe as the hash map is
-	 * allocated in shared memory, which doesn't rely on palloc for memory allocation.
-	 * This is already asserted in hash_search() by Postgres.
+	 * As the hash map is  allocated in shared memory, it doesn't rely on palloc for
+	 * memory allocation, so we could get NULL via HASH_ENTER_NULL. That's why we prefer
+	 * continuing the execution instead of throwing an error.
 	 */
 	bool entryFound = false;
 	SharedConnStatsHashEntry *connectionEntry =

src/backend/distributed/executor/adaptive_executor.c

@@ -2453,9 +2453,9 @@ ManageWorkerPool(WorkerPool *workerPool)
 
 
 /*
- * ConnectionThrottlingRequired contains the logic to decide whether a new connection
- * can be considered as optional or not. When the function return true, the connection
- * can be established with optinal flag, else it should not be an optional connection.
+ * CanUseOptionalConnection contains the logic to decide whether a new connection
+ * can be considered as optional or not. When the function returns true, the connection
+ * can be established with optional flag, else it should not be an optional connection.
  */
 static bool
 CanUseOptionalConnection(WorkerPool *workerPool)
@@ -2483,7 +2483,13 @@ CanUseOptionalConnection(WorkerPool *workerPool)
 	}
 	else if (UseConnectionPerPlacement())
 	{
-		/* user wants one connection per placement, so no throttling is desired */
+		/*
+		 * User wants one connection per placement, so no throttling is desired.
+		 * The primary reason for this is that allowing multiple backends to use
+		 * connection per placement could lead to unresolved self deadlocks. In other
+		 * words, each backend may stuck waiting for other backends to get a slot
+		 * in the shared connection counters.
+		 */
 		return false;
 	}