res_odbc: cache_size option to limit the cached connections.

Signed-off-by: Jaco Kroon <jaco@uls.co.za>

UserNote: New cache_size option for res_odbc to on a per class basis limit the
number of cached connections. Please reference the sample configuration
for details.

configs/samples/res_odbc.conf.sample

@@ -97,6 +97,18 @@ pre-connect => yes
 ; The default remains a stack to be backwards compatible, setting this value to
 ; any of rr, roundrobin or queue will result in a round-robin queue being used.
 ;cache_type => roundrobin
+;
+; Limit the number of connections to cache.  This is separate from
+; max_connections which is the total number of connections that open, whereas
+; this value specifies how many idle connections will be stored in the connection
+; cache.  On extremely spiky loads this could be useful to limit the overall
+; number of connections that's kept open when the spike comes down.  The default
+; is to not limit the cache size (thus effectively limit to max_connections).
+; When a returned connection would result in the cache size being exceeded, the
+; longest idle connection in the cache shall be dropped.
+; Setting this to zero will effectively disable the connection cache, setting to -1
+; will set this to "infinite" (default).
+;cache_size => 10
 
 [mysql2]
 enabled => no

res/res_odbc.c

@@ -101,6 +101,10 @@ struct odbc_class
 	char *sql_text;
 	/*! Slow query limit (in milliseconds) */
 	unsigned int slowquerylimit;
+	/*! Maximum number of cached connections, default is maxconnections */
+	unsigned int max_cache_size;
+	/*! Current cached connection count, when cache_size will exceed max_cache_size, longest-idle connection will be dropped from the cache */
+	unsigned int cur_cache;
 };
 
 static struct ao2_container *class_container;
@@ -564,6 +568,7 @@ static int load_odbc_config(void)
 	struct timeval ncache = { 0, 0 };
 	int preconnect = 0, res = 0, cache_is_queue = 0;
 	struct ast_flags config_flags = { 0 };
+	unsigned int max_cache_size;
 
 	struct odbc_class *new;
 
@@ -591,6 +596,7 @@ static int load_odbc_config(void)
 			logging = 0;
 			slowquerylimit = 5000;
 			cache_is_queue = 0;
+			max_cache_size = UINT_MAX;
 			for (v = ast_variable_browse(config, cat); v; v = v->next) {
 				if (!strcasecmp(v->name, "pooling") ||
 						!strncasecmp(v->name, "share", 5) ||
@@ -650,6 +656,12 @@ static int load_odbc_config(void)
 					cache_is_queue = !strcasecmp(v->value, "rr") ||
 						!strcasecmp(v->value, "roundrobin") ||
 						!strcasecmp(v->value, "queue");
+				} else if (!strcasecmp(v->name, "cache_size")) {
+					if (!strcasecmp(v->value, "-1")) {
+						max_cache_size = UINT_MAX;
+					} else if (sscanf(v->value, "%u", &max_cache_size) != 1) {
+						ast_log(LOG_WARNING, "cache_size must be a non-negative integer or -1 (infinite)\n");
+					}
 				}
 			}
 
@@ -679,6 +691,8 @@ static int load_odbc_config(void)
 				new->logging = logging;
 				new->slowquerylimit = slowquerylimit;
 				new->cache_is_queue = cache_is_queue;
+				new->max_cache_size = max_cache_size;
+				new->cur_cache = 0;
 
 				if (cat)
 					ast_copy_string(new->name, cat, sizeof(new->name));
@@ -766,6 +780,8 @@ static char *handle_cli_odbc_show(struct ast_cli_entry *e, int cmd, struct ast_c
 
 			ast_cli(a->fd, "    Number of active connections: %zd (out of %d)\n", class->connection_cnt, class->maxconnections);
 			ast_cli(a->fd, "    Cache Type: %s\n", class->cache_is_queue ? "round-robin queue" : "stack (last release, first re-use)");
+			ast_cli(a->fd, "    Cache Usage: %u cached out of %u\n", class->cur_cache,
+					class->max_cache_size < class->maxconnections ? class->max_cache_size : class->maxconnections);
 			ast_cli(a->fd, "    Logging: %s\n", class->logging ? "Enabled" : "Disabled");
 			if (class->logging) {
 				ast_cli(a->fd, "    Number of prepares executed: %d\n", class->prepares_executed);
@@ -836,6 +852,29 @@ void ast_odbc_release_obj(struct odbc_obj *obj)
 	} else {
 		AST_LIST_INSERT_HEAD(&class->connections, obj, list);
 	}
+
+	if (class->cur_cache >= class->max_cache_size) {
+		/* cache is full */
+		if (class->cache_is_queue) {
+			/* HEAD will be oldest */
+			obj = AST_LIST_REMOVE_HEAD(&class->connections, list);
+		} else {
+			/* TAIL will be oldest */
+			obj = AST_LIST_LAST(&class->connections);
+			AST_LIST_REMOVE(&class->connections, obj, list);
+		}
+		--class->connection_cnt;
+		ast_mutex_unlock(&class->lock);
+
+		ast_debug(2, "ODBC Pool '%s' exceeded cache size, dropping '%p', connection count is %zd (%u cached)\n",
+			class->name, obj, class->connection_cnt, class->cur_cache);
+
+		ao2_ref(obj, -1);
+
+		ast_mutex_lock(&class->lock);
+	} else {
+		++class->cur_cache;
+	}
 	ast_cond_signal(&class->cond);
 	ast_mutex_unlock(&class->lock);
 
@@ -931,6 +970,9 @@ struct odbc_obj *_ast_odbc_request_obj2(const char *name, struct ast_flags flags
 		ast_mutex_lock(&class->lock);
 
 		obj = AST_LIST_REMOVE_HEAD(&class->connections, list);
+		if (obj) {
+			--class->cur_cache;
+		}
 
 		ast_mutex_unlock(&class->lock);