H2O: Reduce the number of system calls executed for database access (#7918)

frameworks/C/h2o/README.md

@@ -11,8 +11,8 @@ builds directly on top of `libh2o` instead of running the standalone server.
 
 ## Test implementations
 
-The test implementations are located into the `src/handlers` directory - refer to the
-`initialize_*_handler*()` functions.
+The test implementations are located into the [src/handlers](src/handlers) directory - refer to
+the `initialize_*_handler*()` functions.
 
 ## Performance tuning
 

frameworks/C/h2o/src/database.c

@@ -33,11 +33,14 @@
 #include "global_data.h"
 #include "list.h"
 
-#define EXPECT_SYNC 1
-#define IGNORE_RESULT 2
-#define IS_RESETTING 4
 #define MS_IN_S 1000
 
+// Database connection state
+#define EXPECT_SYNC 1
+#define IDLE 2
+#define IGNORE_RESULT 4
+#define RESET 8
+
 typedef struct {
 	list_t l;
 	PGconn *conn;
@@ -147,13 +150,13 @@ static int do_execute_query(db_conn_t *conn, db_query_param_t *param)
 		assert(!h2o_timeout_is_linked(&conn->timeout));
 		conn->timeout.cb = on_database_timeout;
 		h2o_timeout_link(conn->pool->loop, &conn->pool->timeout, &conn->timeout);
-		h2o_socket_read_start(conn->sock, on_database_read_ready);
 	}
 
 	param->l.next = NULL;
 	*conn->queries.tail = &param->l;
 	conn->queries.tail = &param->l.next;
 	conn->query_num--;
+	conn->flags &= ~IDLE;
 	return 0;
 }
 
@@ -235,6 +238,7 @@ static void on_database_connect_read_ready(h2o_socket_t *sock, const char *err)
 					PQclear(result);
 					h2o_timeout_unlink(&conn->timeout);
 					h2o_socket_read_stop(conn->sock);
+					h2o_socket_read_start(conn->sock, on_database_read_ready);
 					process_queries(conn);
 					return;
 				default:
@@ -370,11 +374,13 @@ static void on_database_read_ready(h2o_socket_t *sock, const char *err)
 		else {
 			assert(!result);
 			h2o_timeout_unlink(&conn->timeout);
-			h2o_socket_read_stop(conn->sock);
 			break;
 		}
 	}
 
+	for (PGnotify *notify = PQnotifies(conn->conn); notify; notify = PQnotifies(conn->conn))
+		PQfreemem(notify);
+
 	process_queries(conn);
 }
 
@@ -425,7 +431,7 @@ static void poll_database_connection(h2o_socket_t *sock, const char *err)
 	if (err)
 		ERROR(err);
 	else {
-		const PostgresPollingStatusType status = conn->flags & IS_RESETTING ?
+		const PostgresPollingStatusType status = conn->flags & RESET ?
 		                                         PQresetPoll(conn->conn) :
 		                                         PQconnectPoll(conn->conn);
 		const int sd = PQsocket(conn->conn);
@@ -474,6 +480,7 @@ static void poll_database_connection(h2o_socket_t *sock, const char *err)
 					conn->sock = sock;
 				}
 
+				conn->flags &= ~RESET;
 				prepare_statements(conn);
 				return;
 			case PGRES_POLLING_READING:
@@ -530,8 +537,10 @@ static void prepare_statements(db_conn_t *conn)
 		h2o_socket_read_start(conn->sock, on_database_connect_read_ready);
 		on_database_connect_write_ready(conn->sock, NULL);
 	}
-	else
+	else {
+		h2o_socket_read_start(conn->sock, on_database_read_ready);
 		process_queries(conn);
+	}
 }
 
 static void process_queries(db_conn_t *conn)
@@ -558,9 +567,10 @@ static void process_queries(db_conn_t *conn)
 		}
 	}
 
-	if (!conn->queries.head && !(conn->flags & (EXPECT_SYNC | IGNORE_RESULT))) {
+	if (!conn->queries.head && !(conn->flags & (EXPECT_SYNC | IDLE | IGNORE_RESULT))) {
 		conn->l.next = conn->pool->conn;
 		conn->pool->conn = &conn->l;
+		conn->flags |= IDLE;
 	}
 }
 
@@ -580,7 +590,7 @@ static void start_database_connect(db_conn_pool_t *pool, db_conn_t *conn)
 
 		memset(conn, 0, sizeof(*conn));
 		conn->conn = c;
-		conn->flags = IS_RESETTING;
+		conn->flags = RESET;
 	}
 	else {
 		assert(pool->conn_num);
@@ -642,6 +652,7 @@ int execute_database_query(db_conn_pool_t *pool, db_query_param_t *param)
 		db_conn_t * const conn = H2O_STRUCT_FROM_MEMBER(db_conn_t, l, pool->conn);
 
 		assert(!conn->queries.head);
+		assert(conn->flags & IDLE);
 		assert(!(conn->flags & (EXPECT_SYNC | IGNORE_RESULT)));
 		pool->conn = conn->l.next;
 		ret = do_execute_query(conn, param);
@@ -684,7 +695,8 @@ void free_database_connection_pool(db_conn_pool_t *pool)
 
 			assert(!conn->queries.head);
 			assert(conn->query_num == pool->config->max_pipeline_query_num);
-			assert(!(conn->flags & (EXPECT_SYNC | IGNORE_RESULT)));
+			assert(conn->flags & IDLE);
+			assert(!(conn->flags & (EXPECT_SYNC | IGNORE_RESULT | RESET)));
 			assert(!h2o_timeout_is_linked(&conn->timeout));
 			h2o_socket_read_stop(conn->sock);
 			h2o_socket_close(conn->sock);