Track PID of the remote backend processes serving a particular connection.

This information is usally readily available in PGConn, but since we only pass
around socket descriptors between pooler and the coordinator (or datanode
backends), we pass this information back to the backends. This is at least very
useful for debugging purposes.

(This API definitely deserves some refactoring. In particular, I would like to
keep a copy of some other members of the PGConn structure in the
PGXCNodeHandle, but for now backend PID is what we care for).

5 files changed, 56 insertions, 16 deletions

diff --git a/src/backend/pgxc/pool/pgxcnode.c b/src/backend/pgxc/pool/pgxcnode.c
index 6882d59780..bb8e94c829 100644
--- a/src/backend/pgxc/pool/pgxcnode.c
+++ b/src/backend/pgxc/pool/pgxcnode.c
@@ -111,7 +111,8 @@ static bool DoInvalidateRemoteHandles(void);
 #endif
 
 #ifdef XCP
-static void pgxc_node_init(PGXCNodeHandle *handle, int sock, bool global_session);
+static void pgxc_node_init(PGXCNodeHandle *handle, int sock,
+		bool global_session, int pid);
 #else
 static void pgxc_node_init(PGXCNodeHandle *handle, int sock);
 #endif
@@ -395,11 +396,12 @@ pgxc_node_all_free(void)
  * Structure stores state info and I/O buffers
  */
 static void
-pgxc_node_init(PGXCNodeHandle *handle, int sock, bool global_session)
+pgxc_node_init(PGXCNodeHandle *handle, int sock, bool global_session, int pid)
 {
 	char *init_str;
 
 	handle->sock = sock;
+	handle->backend_pid = pid;
 	handle->transaction_status = 'I';
 	handle->state = DN_CONNECTION_STATE_IDLE;
 	handle->read_only = true;
@@ -1957,10 +1959,13 @@ get_any_handle(List *datanodelist)
 				{
 					/* The node is requested */
 					List   *allocate = list_make1_int(node);
-					int    *fds = PoolManagerGetConnections(allocate, NIL);
+					int	   *pids;
+					int    *fds = PoolManagerGetConnections(allocate, NIL,
+							&pids);
 
 					if (!fds)
 					{
+						Assert(pids != NULL);
 						ereport(ERROR,
 								(errcode(ERRCODE_INSUFFICIENT_RESOURCES),
 								 errmsg("Failed to get pooled connections"),
@@ -1973,7 +1978,7 @@ get_any_handle(List *datanodelist)
 									 "max_connections and max_pool_size configuration "
 									 "parameters")));
 					}
-					pgxc_node_init(&dn_handles[node], fds[0], true);
+					pgxc_node_init(&dn_handles[node], fds[0], true, pids[0]);
 					datanode_count++;
 
 					/*
@@ -2173,7 +2178,8 @@ get_handles(List *datanodelist, List *coordlist, bool is_coord_only_query, bool
 	if (dn_allocate || co_allocate)
 	{
 		int	j = 0;
-		int	*fds = PoolManagerGetConnections(dn_allocate, co_allocate);
+		int *pids;
+		int	*fds = PoolManagerGetConnections(dn_allocate, co_allocate, &pids);
 
 		if (!fds)
 		{
@@ -2207,7 +2213,8 @@ get_handles(List *datanodelist, List *coordlist, bool is_coord_only_query, bool
 			foreach(node_list_item, dn_allocate)
 			{
 				int			node = lfirst_int(node_list_item);
-				int			fdsock = fds[j++];
+				int			fdsock = fds[j];
+				int			be_pid = pids[j++];
 
 				if (node < 0 || node >= NumDataNodes)
 				{
@@ -2217,7 +2224,7 @@ get_handles(List *datanodelist, List *coordlist, bool is_coord_only_query, bool
 				}
 
 				node_handle = &dn_handles[node];
-				pgxc_node_init(node_handle, fdsock, is_global_session);
+				pgxc_node_init(node_handle, fdsock, is_global_session, be_pid);
 				dn_handles[node] = *node_handle;
 				datanode_count++;
 			}
@@ -2228,6 +2235,7 @@ get_handles(List *datanodelist, List *coordlist, bool is_coord_only_query, bool
 			foreach(node_list_item, co_allocate)
 			{
 				int			node = lfirst_int(node_list_item);
+				int			be_pid = pids[j];
 				int			fdsock = fds[j++];
 
 				if (node < 0 || node >= NumCoords)
@@ -2238,7 +2246,7 @@ get_handles(List *datanodelist, List *coordlist, bool is_coord_only_query, bool
 				}
 
 				node_handle = &co_handles[node];
-				pgxc_node_init(node_handle, fdsock, is_global_session);
+				pgxc_node_init(node_handle, fdsock, is_global_session, be_pid);
 				co_handles[node] = *node_handle;
 				coord_count++;
 			}
diff --git a/src/backend/pgxc/pool/poolcomm.c b/src/backend/pgxc/pool/poolcomm.c
index 49a13bbab0..29f88df55d 100644
--- a/src/backend/pgxc/pool/poolcomm.c
+++ b/src/backend/pgxc/pool/poolcomm.c
@@ -793,7 +793,7 @@ pool_recvpids(PoolPort *port, int **pids)
 	{
 		int n;
 		memcpy(&n, buf + 5 + i * sizeof(int), sizeof(int));
-		*pids[i] = ntohl(n);
+		(*pids)[i] = ntohl(n);
 	}
 	return n32;
 
diff --git a/src/backend/pgxc/pool/poolmgr.c b/src/backend/pgxc/pool/poolmgr.c
index 3dac376f05..95514e31a6 100644
--- a/src/backend/pgxc/pool/poolmgr.c
+++ b/src/backend/pgxc/pool/poolmgr.c
@@ -132,7 +132,8 @@ static int	destroy_database_pool(const char *database, const char *user_name);
 static void reload_database_pools(PoolAgent *agent);
 static DatabasePool *find_database_pool(const char *database, const char *user_name, const char *pgoptions);
 static DatabasePool *remove_database_pool(const char *database, const char *user_name);
-static int *agent_acquire_connections(PoolAgent *agent, List *datanodelist, List *coordlist);
+static int *agent_acquire_connections(PoolAgent *agent, List *datanodelist,
+		List *coordlist, int **connectionpids);
 static int cancel_query_on_connections(PoolAgent *agent, List *datanodelist, List *coordlist);
 static PGXCNodePoolSlot *acquire_connection(DatabasePool *dbPool, Oid node);
 static void agent_release_connections(PoolAgent *agent, bool force_destroy);
@@ -905,7 +906,7 @@ PoolManagerDisconnect(void)
  * Get pooled connections
  */
 int *
-PoolManagerGetConnections(List *datanodelist, List *coordlist)
+PoolManagerGetConnections(List *datanodelist, List *coordlist, int **pids)
 {
 	int			i;
 	ListCell   *nodelist_item;
@@ -959,6 +960,13 @@ PoolManagerGetConnections(List *datanodelist, List *coordlist)
 		return NULL;
 	}
 
+	if (pool_recvpids(&poolHandle->port, pids) != totlen)
+	{
+		pfree(*pids);
+		*pids = NULL;
+		return NULL;
+	}
+
 	return fds;
 }
 
@@ -1276,13 +1284,22 @@ agent_handle_input(PoolAgent * agent, StringInfo s)
 				 * In case of error agent_acquire_connections will log
 				 * the error and return NULL
 				 */
-				fds = agent_acquire_connections(agent, datanodelist, coordlist);
+				fds = agent_acquire_connections(agent, datanodelist, coordlist,
+						&pids);
 				list_free(datanodelist);
 				list_free(coordlist);
 
 				pool_sendfds(&agent->port, fds, fds ? datanodecount + coordcount : 0);
 				if (fds)
 					pfree(fds);
+
+				/*
+				 * Also send the PIDs of the remote backend processes serving
+				 * these connections
+				 */
+				pool_sendpids(&agent->port, pids, pids ? datanodecount + coordcount : 0);
+				if (pids)
+					pfree(pids);
 				break;
 
 			case 'h':			/* Cancel SQL Command in progress on specified connections */
@@ -1390,7 +1407,8 @@ agent_handle_input(PoolAgent * agent, StringInfo s)
  * acquire connection
  */
 static int *
-agent_acquire_connections(PoolAgent *agent, List *datanodelist, List *coordlist)
+agent_acquire_connections(PoolAgent *agent, List *datanodelist,
+		List *coordlist, int **pids)
 {
 	int			i;
 	int		   *result;
@@ -1420,6 +1438,14 @@ agent_acquire_connections(PoolAgent *agent, List *datanodelist, List *coordlist)
 				 errmsg("out of memory")));
 	}
 
+	*pids = (int *) palloc((list_length(datanodelist) + list_length(coordlist)) * sizeof(int));
+	if (*pids == NULL)
+	{
+		ereport(ERROR,
+				(errcode(ERRCODE_OUT_OF_MEMORY),
+				 errmsg("out of memory")));
+	}
+
 	/*
 	 * There are possible memory allocations in the core pooler, we want
 	 * these allocations in the contect of the database pool
@@ -1458,7 +1484,8 @@ agent_acquire_connections(PoolAgent *agent, List *datanodelist, List *coordlist)
 			 */
 		}
 
-		result[i++] = PQsocket((PGconn *) agent->dn_connections[node]->conn);
+		result[i] = PQsocket((PGconn *) agent->dn_connections[node]->conn);
+		(*pids)[i++] = ((PGconn *) agent->dn_connections[node]->conn)->be_pid;
 	}
 
 	/* Save then in the array fds for Coordinators */
@@ -1489,7 +1516,8 @@ agent_acquire_connections(PoolAgent *agent, List *datanodelist, List *coordlist)
 			 */
 		}
 
-		result[i++] = PQsocket((PGconn *) agent->coord_connections[node]->conn);
+		result[i] = PQsocket((PGconn *) agent->coord_connections[node]->conn);
+		(*pids)[i++] = ((PGconn *) agent->coord_connections[node]->conn)->be_pid;
 	}
 
 	MemoryContextSwitchTo(oldcontext);
diff --git a/src/include/pgxc/pgxcnode.h b/src/include/pgxc/pgxcnode.h
index 789d7cecbc..d57aabe18b 100644
--- a/src/include/pgxc/pgxcnode.h
+++ b/src/include/pgxc/pgxcnode.h
@@ -66,6 +66,9 @@ struct pgxc_node_handle
 
 	/* fd of the connection */
 	int		sock;
+	/* pid of the remote backend process */
+	int		backend_pid;
+
 	/* Connection state */
 	char		transaction_status;
 	DNConnectionState state;
diff --git a/src/include/pgxc/poolmgr.h b/src/include/pgxc/poolmgr.h
index e9f5bbd189..2b8ad5dbef 100644
--- a/src/include/pgxc/poolmgr.h
+++ b/src/include/pgxc/poolmgr.h
@@ -117,7 +117,8 @@ extern char *session_options(void);
 extern void PoolManagerReconnect(void);
 
 /* Get pooled connections */
-extern int *PoolManagerGetConnections(List *datanodelist, List *coordlist);
+extern int *PoolManagerGetConnections(List *datanodelist, List *coordlist,
+		int **pids);
 
 /* Clean pool connections */
 extern void PoolManagerCleanConnection(List *datanodelist, List *coordlist, char *dbname, char *username);