H2O: Optimize the implementation further

* Reduce the maximum number of connections accepted simultaneously
from 2 to 1 in order to improve load balancing among the threads.
* Reduce the maximum number of database connections per thread from
8 to 5 in order to improve performance when the application server
has more processors than the database server.
* Avoid some memory copying for larger responses.
* Update H2O to version 2.1.0-beta3.
* Increase the default cache line size from 64 to 128 bytes and
improve the runtime detection error handling.
* Add some comments and diagnostic messages.

frameworks/C/h2o/setup.sh

@@ -25,7 +25,7 @@ run_curl()
 
 run_h2o_app()
 {
-	"$1/h2o_app" -a2 -f "$2/template/fortunes.mustache" -m8 "$3" "$4" \
+	"$1/h2o_app" -a1 -f "$2/template/fortunes.mustache" -m5 "$3" "$4" \
 		-d "host=$DBHOST dbname=hello_world user=benchmarkdbuser password=benchmarkdbpass" &
 }
 

frameworks/C/h2o/src/fortune.c

@@ -59,6 +59,7 @@ static uintmax_t add_iovec(mustache_api_t *api,
                            void *userdata,
                            const char *buffer,
                            uintmax_t buffer_size);
+static void cleanup_fortunes(void *data);
 static int compare_fortunes(const list_t *x, const list_t *y);
 static void complete_fortunes(struct st_h2o_generator_t *self, h2o_req_t *req);
 static list_t *get_sorted_sublist(list_t *head);
@@ -109,6 +110,22 @@ static uintmax_t add_iovec(mustache_api_t *api,
 	return ret;
 }
 
+static void cleanup_fortunes(void *data)
+{
+	fortune_ctx_t * const fortune_ctx = data;
+	const list_t *iter = fortune_ctx->result;
+
+	if (iter)
+		do {
+			const fortune_t * const fortune = H2O_STRUCT_FROM_MEMBER(fortune_t, l, iter);
+
+			if (fortune->data)
+				PQclear(fortune->data);
+
+			iter = iter->next;
+		} while (iter);
+}
+
 static int compare_fortunes(const list_t *x, const list_t *y)
 {
 	const fortune_t * const f1 = H2O_STRUCT_FROM_MEMBER(fortune_t, l, x);
@@ -209,40 +226,33 @@ static result_return_t on_fortune_result(db_query_param_t *param, PGresult *resu
 		ret = SUCCESS;
 
 		for (size_t i = 0; i < num_rows; i++) {
-			const char * const message_data = PQgetvalue(result, i, 1);
-			h2o_iovec_t message = h2o_htmlescape(&fortune_ctx->req->pool,
-			                                     message_data,
-			                                     PQgetlength(result, i, 1));
-			const size_t id_len = PQgetlength(result, i, 0);
-			const size_t fortune_size = offsetof(fortune_t, data) + id_len +
-			                            (message_data == message.base ? message.len : 0);
 			fortune_t * const fortune = h2o_mem_alloc_pool(&fortune_ctx->req->pool,
-			                                               fortune_size);
+			                                               sizeof(*fortune));
 
 			if (fortune) {
-				memset(fortune, 0, offsetof(fortune_t, data));
-				memcpy(fortune->data, PQgetvalue(result, i, 0), id_len);
-				fortune->id.base = fortune->data;
-				fortune->id.len = id_len;
-
-				if (message_data == message.base) {
-					message.base = fortune->data + id_len;
-					memcpy(message.base, message_data, message.len);
-				}
-
-				fortune->message = message;
+				memset(fortune, 0, sizeof(*fortune));
+				fortune->id.base = PQgetvalue(result, i, 0);
+				fortune->id.len = PQgetlength(result, i, 0);
+				fortune->message = h2o_htmlescape(&fortune_ctx->req->pool,
+				                                  PQgetvalue(result, i, 1),
+				                                  PQgetlength(result, i, 1));
 				fortune->l.next = fortune_ctx->result;
 				fortune_ctx->result = &fortune->l;
 				fortune_ctx->num_result++;
+
+				if (!i)
+					fortune->data = result;
 			}
 			else {
 				send_error(INTERNAL_SERVER_ERROR, MEM_ALLOC_ERR_MSG, fortune_ctx->req);
 				ret = DONE;
+
+				if (!i)
+					PQclear(result);
+
 				break;
 			}
 		}
-
-		PQclear(result);
 	}
 	else if (result) {
 		PQclear(result);
@@ -365,7 +375,9 @@ int fortunes(struct st_h2o_handler_t *self, h2o_req_t *req)
 	thread_context_t * const ctx = H2O_STRUCT_FROM_MEMBER(thread_context_t,
 	                                                      event_loop.h2o_ctx,
 	                                                      req->conn->ctx);
-	fortune_ctx_t * const fortune_ctx = h2o_mem_alloc_pool(&req->pool, sizeof(*fortune_ctx));
+	fortune_ctx_t * const fortune_ctx = h2o_mem_alloc_shared(&req->pool,
+	                                                         sizeof(*fortune_ctx),
+	                                                         cleanup_fortunes);
 
 	if (fortune_ctx) {
 		fortune_t * const fortune = h2o_mem_alloc_pool(&req->pool, sizeof(*fortune));
@@ -390,6 +402,8 @@ int fortunes(struct st_h2o_handler_t *self, h2o_req_t *req)
 			if (execute_query(ctx, &fortune_ctx->param))
 				send_service_unavailable_error(DB_REQ_ERROR, req);
 		}
+		else
+			send_error(INTERNAL_SERVER_ERROR, MEM_ALLOC_ERR_MSG, req);
 	}
 	else
 		send_error(INTERNAL_SERVER_ERROR, MEM_ALLOC_ERR_MSG, req);

frameworks/C/h2o/src/fortune.h

@@ -28,9 +28,9 @@
 
 typedef struct {
 	list_t l;
+	PGresult *data;
 	h2o_iovec_t id;
 	h2o_iovec_t message;
-	char data[];
 } fortune_t;
 
 int fortunes(struct st_h2o_handler_t *self, h2o_req_t *req);

frameworks/C/h2o/src/main.c

@@ -179,7 +179,12 @@ static int initialize_global_data(const config_t *config, global_data_t *global_
 	memset(global_data, 0, sizeof(*global_data));
 	global_data->config = config;
 	global_data->memory_alignment = get_maximum_cache_line_size();
-	assert(global_data->memory_alignment <= DEFAULT_CACHE_LINE_SIZE);
+
+	if (global_data->memory_alignment > DEFAULT_CACHE_LINE_SIZE) {
+		ERROR("Unexpected maximum cache line size.");
+		return EXIT_FAILURE;
+	}
+
 	CHECK_ERRNO(sigemptyset, &signals);
 #ifdef NDEBUG
 	CHECK_ERRNO(sigaddset, &signals, SIGINT);
@@ -222,8 +227,12 @@ static int initialize_global_data(const config_t *config, global_data_t *global_
 
 	global_data->ctx = initialize_thread_contexts(global_data);
 
-	if (global_data->ctx)
+	if (global_data->ctx) {
+		printf("Number of processors: %zu\nMaximum cache line size: %zu\n",
+		       h2o_numproc(),
+		       global_data->memory_alignment);
 		return EXIT_SUCCESS;
+	}
 
 error:
 	free_global_data(global_data);

frameworks/C/h2o/src/request_handler.c

@@ -20,6 +20,7 @@
 #include <assert.h>
 #include <h2o.h>
 #include <stdalign.h>
+#include <stdbool.h>
 #include <stdint.h>
 #include <string.h>
 #include <yajl/yajl_gen.h>
@@ -48,7 +49,9 @@ static int json_serializer(struct st_h2o_handler_t *self, h2o_req_t *req)
 		CHECK_YAJL_STATUS(yajl_gen_string, gen, YAJL_STRLIT(HELLO_RESPONSE));
 		CHECK_YAJL_STATUS(yajl_gen_map_close, gen);
 
-		if (!send_json_response(gen, NULL, req))
+		// The response is small enough, so that it is simpler to copy it
+		// instead of doing a delayed deallocation of the JSON generator.
+		if (!send_json_response(gen, true, req))
 			return 0;
 
 error_yajl:
@@ -169,31 +172,29 @@ void send_error(http_status_code_t status_code, const char *body, h2o_req_t *req
 	h2o_send_error_generic(req, status_code, status_code_to_string(status_code), body, 0);
 }
 
-int send_json_response(yajl_gen gen, h2o_generator_t *h2o_generator, h2o_req_t *req)
+int send_json_response(yajl_gen gen, bool free_gen, h2o_req_t *req)
 {
 	const unsigned char *buf;
-	h2o_iovec_t h2o_iovec = {.len = 0};
+	size_t len;
 	int ret = EXIT_FAILURE;
 
-	if (yajl_gen_get_buf(gen, &buf, &h2o_iovec.len) == yajl_gen_status_ok) {
-		if (h2o_generator) {
-			h2o_iovec.base = (char *) buf;
-			set_default_response_param(JSON, SIZE_MAX, req);
-			h2o_start_response(req, h2o_generator);
-			h2o_send(req, &h2o_iovec, 1, false);
-			ret = EXIT_SUCCESS;
-		}
-		else {
-			h2o_iovec.base = h2o_mem_alloc_pool(&req->pool, h2o_iovec.len);
+	if (yajl_gen_get_buf(gen, &buf, &len) == yajl_gen_status_ok) {
+		if (free_gen) {
+			char * const body = h2o_mem_alloc_pool(&req->pool, len);
 
-			if (h2o_iovec.base) {
-				memcpy(h2o_iovec.base, buf, h2o_iovec.len);
+			if (body) {
+				memcpy(body, buf, len);
 				yajl_gen_free(gen);
-				set_default_response_param(JSON, h2o_iovec.len, req);
-				h2o_send_inline(req, h2o_iovec.base, h2o_iovec.len);
+				set_default_response_param(JSON, len, req);
+				h2o_send_inline(req, body, len);
 				ret = EXIT_SUCCESS;
 			}
 		}
+		else {
+			set_default_response_param(JSON, len, req);
+			h2o_send_inline(req, (char *) buf, len);
+			ret = EXIT_SUCCESS;
+		}
 	}
 
 	return ret;

frameworks/C/h2o/src/request_handler.h

@@ -22,6 +22,7 @@
 #define REQUEST_H_
 
 #include <h2o.h>
+#include <stdbool.h>
 #include <yajl/yajl_gen.h>
 
 typedef enum {
@@ -44,7 +45,7 @@ const char *get_query_param(const char *query,
                             size_t param_len);
 void register_request_handlers(h2o_hostconf_t *hostconf, h2o_access_log_filehandle_t *log_handle);
 void send_error(http_status_code_t status_code, const char *body, h2o_req_t *req);
-int send_json_response(yajl_gen gen, h2o_generator_t *h2o_generator, h2o_req_t *req);
+int send_json_response(yajl_gen gen, bool free_gen, h2o_req_t *req);
 void send_service_unavailable_error(const char *body, h2o_req_t *req);
 void set_default_response_param(content_type_t content_type,
                                 size_t content_length,

frameworks/C/h2o/src/thread.h

@@ -30,7 +30,7 @@
 #include "event_loop.h"
 #include "utility.h"
 
-#define DEFAULT_CACHE_LINE_SIZE 64
+#define DEFAULT_CACHE_LINE_SIZE 128
 
 typedef struct thread_context_t thread_context_t;
 
@@ -42,7 +42,7 @@ struct thread_context_t {
 	event_loop_t event_loop;
 	pthread_t thread;
 	// Align on the cache line size to prevent false sharing.
-	char padding[49];
+	char padding[89];
 };
 
 static_assert(!(sizeof(thread_context_t) % DEFAULT_CACHE_LINE_SIZE),

frameworks/C/h2o/src/utility.h

@@ -67,7 +67,11 @@ typedef struct {
 	h2o_globalconf_t h2o_config;
 } global_data_t;
 
+// Call yajl_gen_free() on the result, even though the JSON generator
+// uses a memory pool; in this way the code remains correct if the
+// underlying memory allocator is changed (e.g. for debugging purposes).
 yajl_gen get_json_generator(h2o_mem_pool_t *pool);
+
 uint32_t get_random_number(uint32_t max_rand, unsigned int *seed);
 
 #endif // UTILITY_H_

frameworks/C/h2o/src/world.c

@@ -53,7 +53,6 @@ typedef struct {
 
 typedef struct {
 	db_query_param_t param;
-	yajl_gen gen;
 	const char *id_pointer;
 	h2o_req_t *req;
 	uint32_t id;
@@ -63,16 +62,18 @@ typedef struct {
 
 typedef struct {
 	single_query_ctx_t single;
+	yajl_gen gen;
 	size_t num_query;
 	size_t num_result;
 	update_state_t update_state;
 	query_result_t res[];
 } multiple_query_ctx_t;
 
+static void cleanup_request(void *data);
 static int do_multiple_queries(update_state_t update_state, h2o_req_t *req);
-static int initialize_single_query_context(h2o_req_t *req,
-                                           on_result_t on_result,
-                                           single_query_ctx_t *query_ctx);
+static void initialize_single_query_context(h2o_req_t *req,
+                                            on_result_t on_result,
+                                            single_query_ctx_t *query_ctx);
 static void on_database_error(db_query_param_t *param, const char *error_string);
 static void on_database_timeout(db_query_param_t *param);
 static result_return_t on_multiple_query_result(db_query_param_t *param, PGresult *result);
@@ -85,6 +86,14 @@ static void serialize_items(const query_result_t *res,
                             yajl_gen gen,
                             h2o_req_t *req);
 
+static void cleanup_request(void *data)
+{
+	const multiple_query_ctx_t * const query_ctx = data;
+
+	if (query_ctx->gen)
+		yajl_gen_free(query_ctx->gen);
+}
+
 static int do_multiple_queries(update_state_t update_state, h2o_req_t *req)
 {
 	thread_context_t * const ctx = H2O_STRUCT_FROM_MEMBER(thread_context_t,
@@ -108,16 +117,13 @@ static int do_multiple_queries(update_state_t update_state, h2o_req_t *req)
 		num_query = MAX_QUERIES;
 
 	const size_t sz = offsetof(multiple_query_ctx_t, res) + num_query * sizeof(query_result_t);
-	multiple_query_ctx_t * const query_ctx = h2o_mem_alloc_pool(&req->pool, sz);
+	multiple_query_ctx_t * const query_ctx = h2o_mem_alloc_shared(&req->pool, sz, cleanup_request);
 
-	if (!query_ctx || initialize_single_query_context(req,
-	                                                  on_multiple_query_result,
-	                                                  &query_ctx->single))
-		send_error(INTERNAL_SERVER_ERROR, MEM_ALLOC_ERR_MSG, req);
-	else {
+	if (query_ctx) {
 		// MAX_ID is a relatively small number, so allocate on the stack.
 		DEFINE_BITSET(bitset, MAX_ID);
 
+		initialize_single_query_context(req, on_multiple_query_result, &query_ctx->single);
 		memset(&query_ctx->single + 1,
 		       0,
 		       offsetof(multiple_query_ctx_t, res) - sizeof(query_ctx->single));
@@ -138,43 +144,37 @@ static int do_multiple_queries(update_state_t update_state, h2o_req_t *req)
 
 		query_ctx->single.id = htonl(query_ctx->res->id);
 
-		if (execute_query(ctx, &query_ctx->single.param)) {
-			yajl_gen_free(query_ctx->single.gen);
+		if (execute_query(ctx, &query_ctx->single.param))
 			send_service_unavailable_error(DB_REQ_ERROR, req);
-		}
+		else
+			// Create a JSON generator while the query is processed.
+			query_ctx->gen = get_json_generator(&req->pool);
 	}
+	else
+		send_error(INTERNAL_SERVER_ERROR, MEM_ALLOC_ERR_MSG, req);
 
 	return 0;
 }
 
-static int initialize_single_query_context(h2o_req_t *req,
-                                           on_result_t on_result,
-                                           single_query_ctx_t *query_ctx)
+static void initialize_single_query_context(h2o_req_t *req,
+                                            on_result_t on_result,
+                                            single_query_ctx_t *query_ctx)
 {
-	int ret = EXIT_FAILURE;
-
 	memset(query_ctx, 0, sizeof(*query_ctx));
-	query_ctx->gen = get_json_generator(&req->pool);
-
-	if (query_ctx->gen) {
-		query_ctx->id_format = 1;
-		query_ctx->id_len = sizeof(query_ctx->id);
-		query_ctx->id_pointer = (const char *) &query_ctx->id;
-		query_ctx->param.command = WORLD_TABLE_NAME;
-		query_ctx->param.nParams = 1;
-		query_ctx->param.on_error = on_database_error;
-		query_ctx->param.on_result = on_result;
-		query_ctx->param.on_timeout = on_database_timeout;
-		query_ctx->param.paramFormats = &query_ctx->id_format;
-		query_ctx->param.paramLengths = &query_ctx->id_len;
-		query_ctx->param.paramValues = &query_ctx->id_pointer;
-		query_ctx->param.flags = IS_PREPARED;
-		query_ctx->param.resultFormat = 1;
-		query_ctx->req = req;
-		ret = EXIT_SUCCESS;
-	}
-
-	return ret;
+	query_ctx->id_format = 1;
+	query_ctx->id_len = sizeof(query_ctx->id);
+	query_ctx->id_pointer = (const char *) &query_ctx->id;
+	query_ctx->param.command = WORLD_TABLE_NAME;
+	query_ctx->param.nParams = 1;
+	query_ctx->param.on_error = on_database_error;
+	query_ctx->param.on_result = on_result;
+	query_ctx->param.on_timeout = on_database_timeout;
+	query_ctx->param.paramFormats = &query_ctx->id_format;
+	query_ctx->param.paramLengths = &query_ctx->id_len;
+	query_ctx->param.paramValues = &query_ctx->id_pointer;
+	query_ctx->param.flags = IS_PREPARED;
+	query_ctx->param.resultFormat = 1;
+	query_ctx->req = req;
 }
 
 static void on_database_error(db_query_param_t *param, const char *error_string)
@@ -183,7 +183,6 @@ static void on_database_error(db_query_param_t *param, const char *error_string)
 	                                                              param,
 	                                                              param);
 
-	yajl_gen_free(query_ctx->gen);
 	send_error(BAD_GATEWAY, error_string, query_ctx->req);
 }
 
@@ -193,7 +192,6 @@ static void on_database_timeout(db_query_param_t *param)
 	                                                              param,
 	                                                              param);
 
-	yajl_gen_free(query_ctx->gen);
 	send_error(GATEWAY_TIMEOUT, DB_TIMEOUT_ERROR, query_ctx->req);
 }
 
@@ -228,7 +226,7 @@ static result_return_t on_multiple_query_result(db_query_param_t *param, PGresul
 		else if (query_ctx->update_state == NO_UPDATE) {
 			serialize_items(query_ctx->res,
 			                query_ctx->num_result,
-			                query_ctx->single.gen,
+			                query_ctx->gen,
 			                query_ctx->single.req);
 			return DONE;
 		}
@@ -253,7 +251,6 @@ static result_return_t on_multiple_query_result(db_query_param_t *param, PGresul
 		PQclear(result);
 	}
 
-	yajl_gen_free(query_ctx->single.gen);
 	return DONE;
 }
 
@@ -275,9 +272,17 @@ static result_return_t on_single_query_result(db_query_param_t *param, PGresult
 		random_number = ntohl(random_number);
 		PQclear(result);
 
-		if (!serialize_item(ntohl(query_ctx->id), random_number, query_ctx->gen) &&
-		    !send_json_response(query_ctx->gen, NULL, query_ctx->req))
-			return DONE;
+		const yajl_gen gen = get_json_generator(&query_ctx->req->pool);
+
+		if (gen) {
+			// The response is small enough, so that it is simpler to copy it
+			// instead of doing a delayed deallocation of the JSON generator.
+			if (!serialize_item(ntohl(query_ctx->id), random_number, gen) &&
+			    !send_json_response(gen, true, query_ctx->req))
+				return DONE;
+
+			yajl_gen_free(gen);
+		}
 
 		send_error(INTERNAL_SERVER_ERROR, MEM_ALLOC_ERR_MSG, query_ctx->req);
 	}
@@ -286,7 +291,6 @@ static result_return_t on_single_query_result(db_query_param_t *param, PGresult
 		PQclear(result);
 	}
 
-	yajl_gen_free(query_ctx->gen);
 	return DONE;
 }
 
@@ -318,7 +322,7 @@ static result_return_t on_update_result(db_query_param_t *param, PGresult *resul
 
 			serialize_items(query_ctx->res,
 			                query_ctx->num_result,
-			                query_ctx->single.gen,
+			                query_ctx->gen,
 			                query_ctx->single.req);
 			ret = DONE;
 			break;
@@ -329,7 +333,6 @@ static result_return_t on_update_result(db_query_param_t *param, PGresult *resul
 	PQclear(result);
 	return ret;
 error:
-	yajl_gen_free(query_ctx->single.gen);
 	send_error(BAD_GATEWAY, PQresultErrorMessage(result), query_ctx->single.req);
 	PQclear(result);
 	return DONE;
@@ -419,19 +422,25 @@ static void serialize_items(const query_result_t *res,
                             yajl_gen gen,
                             h2o_req_t *req)
 {
-	CHECK_YAJL_STATUS(yajl_gen_array_open, gen);
+	// In principle the JSON generator can be created here, but we do it earlier,
+	// so that it happens in parallel with the database query; we assume that the
+	// allocation will rarely fail, so that the delayed error handling is not
+	// problematic.
+	if (gen) {
+		CHECK_YAJL_STATUS(yajl_gen_array_open, gen);
 
-	for (size_t i = 0; i < num_result; i++)
-		if (serialize_item(res[i].id, res[i].random_number, gen))
-			goto error_yajl;
+		for (size_t i = 0; i < num_result; i++)
+			if (serialize_item(res[i].id, res[i].random_number, gen))
+				goto error_yajl;
 
-	CHECK_YAJL_STATUS(yajl_gen_array_close, gen);
+		CHECK_YAJL_STATUS(yajl_gen_array_close, gen);
 
-	if (send_json_response(gen, NULL, req)) {
-error_yajl:
-		yajl_gen_free(gen);
-		send_error(INTERNAL_SERVER_ERROR, MEM_ALLOC_ERR_MSG, req);
+		if (!send_json_response(gen, false, req))
+			return;
 	}
+
+error_yajl:
+	send_error(INTERNAL_SERVER_ERROR, MEM_ALLOC_ERR_MSG, req);
 }
 
 int multiple_queries(struct st_h2o_handler_t *self, h2o_req_t *req)
@@ -450,18 +459,15 @@ int single_query(struct st_h2o_handler_t *self, h2o_req_t *req)
 	                                                      req->conn->ctx);
 	single_query_ctx_t * const query_ctx = h2o_mem_alloc_pool(&req->pool, sizeof(*query_ctx));
 
-	if (!query_ctx || initialize_single_query_context(req,
-	                                                  on_single_query_result,
-	                                                  query_ctx))
-		send_error(INTERNAL_SERVER_ERROR, MEM_ALLOC_ERR_MSG, req);
-	else {
+	if (query_ctx) {
+		initialize_single_query_context(req, on_single_query_result, query_ctx);
 		query_ctx->id = htonl(get_random_number(MAX_ID, &ctx->random_seed) + 1);
 
-		if (execute_query(ctx, &query_ctx->param)) {
-			yajl_gen_free(query_ctx->gen);
+		if (execute_query(ctx, &query_ctx->param))
 			send_service_unavailable_error(DB_REQ_ERROR, req);
-		}
 	}
+	else
+		send_error(INTERNAL_SERVER_ERROR, MEM_ALLOC_ERR_MSG, req);
 
 	return 0;
 }

toolset/setup/linux/webservers/h2o.sh

@@ -6,7 +6,7 @@ RETCODE=$(fw_exists "${IROOT}/h2o.installed")
   return 0; }
 
 H2O_HOME="${IROOT}/h2o"
-VERSION="2.1.0-beta1"
+VERSION="2.1.0-beta3"
 ARCHIVE="v${VERSION}.tar.gz"
 BUILD_DIR="h2o-${VERSION}"