Improved connection management to clustrix supporting round robin and fail over

storage/xpand/ha_xpand.cc

@@ -8,6 +8,7 @@ Copyright (c) 2019, MariaDB Corporation.
 #include "ha_xpand_pushdown.h"
 #include "key.h"
 #include <strfunc.h>                            /* strconvert */
+#include "my_pthread.h"
 
 handlerton *xpand_hton = NULL;
 
@@ -41,69 +42,100 @@ static MYSQL_SYSVAR_INT
   NULL, NULL, -1, -1, 2147483647, 0
 );
 
-char *xpand_host;
-static MYSQL_SYSVAR_STR
+//state for load balancing
+int xpand_hosts_cur; //protected by my_atomic's
+ulong xpand_balance_algorithm;
+const char* balance_algorithm_names[]=
+{
+  "first", "round_robin", NullS
+};
+
+TYPELIB balance_algorithms=
+{
+  array_elements(balance_algorithm_names) - 1, "",
+  balance_algorithm_names, NULL
+};
+
+static void update_balance_algorithm(MYSQL_THD thd, struct st_mysql_sys_var *var,
+                                     void *var_ptr, const void *save)
+{
+  *static_cast<ulong *>(var_ptr) = *static_cast<const ulong *>(save);
+  my_atomic_store32(&xpand_hosts_cur, 0);
+}
+
+static MYSQL_SYSVAR_ENUM
 (
-  host,
-  xpand_host,
-  PLUGIN_VAR_OPCMDARG | PLUGIN_VAR_MEMALLOC,
-  "Xpand host",
-  NULL, NULL, "127.0.0.1"
+  balance_algorithm,
+  xpand_balance_algorithm,
+  PLUGIN_VAR_OPCMDARG,
+  "Method for managing load balancing of Clustrix nodes, can take values FIRST or ROUND_ROBIN",
+  NULL, update_balance_algorithm, XPAND_BALANCE_ROUND_ROBIN, &balance_algorithms
 );
 
-int host_list_cnt;
-char **host_list;
+//current list of clx hosts
+static PSI_rwlock_key key_xpand_hosts;
+mysql_rwlock_t xpand_hosts_lock;
+xpand_host_list *xpand_hosts;
 
-static void free_host_list()
+//only call while holding lock
+static void clear_hosts()
 {
-  if (host_list) {
-    for (int i = 0; host_list[i]; i++)
-      my_free(host_list[i]);
-    my_free(host_list);
-    host_list = NULL;
-  }
+  delete xpand_hosts;
+  xpand_hosts = NULL;
+  my_atomic_store32(&xpand_hosts_cur, 0);
 }
 
-static void update_host_list(char *xpand_host)
+static int check_hosts(MYSQL_THD thd, struct st_mysql_sys_var *var,
+                       void *save, struct st_mysql_value *value)
 {
-  free_host_list();
+  char b;
+  int len = 0;
+  const char *val = value->val_str(value, &b, &len);
 
-  int cnt = 0;
-  for (char *p = xpand_host, *s = xpand_host; ; p++) {
-    if (*p == ',' || *p == '\0') {
-      if (p > s) {
-        cnt++;
-      }
-      if (!*p)
-        break;
-      s = p + 1;
-    }
-  }
+  if (!val)
+    return HA_ERR_OUT_OF_MEM;
 
-  DBUG_PRINT("host_cnt", ("%d", cnt));
-  host_list = (char **)my_malloc(sizeof(char *) * cnt+1, MYF(MY_WME));
-  host_list[cnt] = 0;
-  host_list_cnt = cnt;
-
-  int i = 0;
-  for (char *p = xpand_host, *s = xpand_host; ; p++) {
-    if (*p == ',' || *p == '\0') {
-      if (p > s) {
-        char *host = (char *)my_malloc(p - s + 1, MYF(MY_WME));
-        host[p-s] = '\0';
-        memcpy(host, s, p-s);
-        DBUG_PRINT("host", ("%s", host));
-        host_list[i++] = host;
-      }
-      if (!*p)
-        break;
-      s = p + 1;
-    }
+  int error_code = 0;
+  xpand_host_list *host_list = xpand_host_list::create(val, thd, &error_code);
+  if (error_code)
+    return error_code;
+
+  *static_cast<xpand_host_list**>(save) = host_list;
+  return 0;
+}
+
+static void update_hosts(MYSQL_THD thd, struct st_mysql_sys_var *var,
+                         void *var_ptr, const void *save)
+{
+  mysql_rwlock_wrlock(&xpand_hosts_lock);
+
+  xpand_host_list *from_save = *static_cast<xpand_host_list * const *>(save);
+  char* raw = from_save->full_list;
+
+  int error_code = 0;
+  xpand_host_list *new_hosts = xpand_host_list::create(raw, &error_code);
+  if (error_code) {
+    my_printf_error(error_code, "Unhandled error setting xpand hostlist", MYF(0));
+    return;
   }
 
-  DBUG_PRINT("xpand_host", ("%s", xpand_host));
+  clear_hosts();
+  xpand_hosts = new_hosts;
+  *static_cast<char**>(var_ptr) = new_hosts->full_list;
+
+  mysql_rwlock_unlock(&xpand_hosts_lock);
 }
 
+static char *xpand_hosts_str;
+static MYSQL_SYSVAR_STR
+(
+  hosts,
+  xpand_hosts_str,
+  PLUGIN_VAR_OPCMDARG | PLUGIN_VAR_MEMALLOC,
+  "List of xpand hostnames seperated by commas, semicolons or spaces",
+  check_hosts, update_hosts, "localhost"
+);
+
 char *xpand_username;
 static MYSQL_SYSVAR_STR
 (
@@ -1403,15 +1435,20 @@ static int xpand_init(void *p)
   xpand_hton->create_select = create_xpand_select_handler;
   xpand_hton->create_derived = create_xpand_derived_handler;
 
-  update_host_list(xpand_host);
-
-  DBUG_RETURN(0);
+  mysql_rwlock_init(key_xpand_hosts, &xpand_hosts_lock);
+  mysql_rwlock_wrlock(&xpand_hosts_lock);
+  int error_code = 0;
+  xpand_hosts = xpand_host_list::create(xpand_hosts_str, &error_code);
+  mysql_rwlock_unlock(&xpand_hosts_lock);
+  DBUG_RETURN(error_code);
 }
 
 static int xpand_deinit(void *p)
 {
   DBUG_ENTER("xpand_deinit");
-  free_host_list();
+  mysql_rwlock_wrlock(&xpand_hosts_lock);
+  delete xpand_hosts;
+  mysql_rwlock_destroy(&xpand_hosts_lock);
   DBUG_RETURN(0);
 }
 
@@ -1425,7 +1462,8 @@ static struct st_mysql_sys_var* xpand_system_variables[] =
   MYSQL_SYSVAR(connect_timeout),
   MYSQL_SYSVAR(read_timeout),
   MYSQL_SYSVAR(write_timeout),
-  MYSQL_SYSVAR(host),
+  MYSQL_SYSVAR(balance_algorithm),
+  MYSQL_SYSVAR(hosts),
   MYSQL_SYSVAR(username),
   MYSQL_SYSVAR(password),
   MYSQL_SYSVAR(port),

storage/xpand/xpand_connection.cc

@@ -10,6 +10,7 @@ Copyright (c) 2019, MariaDB Corporation.
 #include "handler.h"
 #include "table.h"
 #include "sql_class.h"
+#include "my_pthread.h"
 #include "tztime.h"
 
 //#include "errmsg.h"
@@ -125,30 +126,42 @@ void xpand_connection::disconnect(bool is_destructor)
   DBUG_VOID_RETURN;
 }
 
-int host_list_next;
-extern int host_list_cnt;
-extern char **host_list;
+extern int xpand_hosts_cur;
+extern ulong xpand_balance_algorithm;
+
+extern mysql_rwlock_t xpand_hosts_lock;
+extern xpand_host_list *xpand_hosts;
 
 int xpand_connection::connect()
 {
-  int error_code = 0;
-  my_bool my_true = 1;
   DBUG_ENTER("xpand_connection::connect");
+  int start = 0;
+  if (xpand_balance_algorithm == XPAND_BALANCE_ROUND_ROBIN)
+    start = my_atomic_add32(&xpand_hosts_cur, 1);
 
-  // cpu concurrency by damned!
-  int host_num = host_list_next;
-  host_num = host_num % host_list_cnt;
-  char *host = host_list[host_num];
-  host_list_next = host_num + 1;
-  DBUG_PRINT("host", ("%s", host));
+  mysql_rwlock_rdlock(&xpand_hosts_lock);
 
-  /* Validate the connection parameters */
-  if (!strcmp(xpand_socket, ""))
-    if (!strcmp(host, "127.0.0.1"))
-      if (xpand_port == MYSQL_PORT_DEFAULT)
-        DBUG_RETURN(ER_CONNECT_TO_FOREIGN_DATA_SOURCE);
+  //search for available host
+  int error_code = 0;
+  for (int i = 0; i < xpand_hosts->hosts_len; i++) {
+    char *host = xpand_hosts->hosts[(start + i) % xpand_hosts->hosts_len];
+    error_code = connect_direct(host);
+    if (!error_code)
+      break;
+  }
+  mysql_rwlock_unlock(&xpand_hosts_lock);
+  if (error_code)
+    my_error(error_code, MYF(0), "clustrix");
+
+  DBUG_RETURN(error_code);
+}
 
-  //xpand_net.methods = &connection_methods;
+
+int xpand_connection::connect_direct(char *host)
+{
+  DBUG_ENTER("xpand_connection::connect_direct");
+  my_bool my_true = true;
+  DBUG_PRINT("host", ("%s", host));
 
   if (!mysql_init(&xpand_net))
     DBUG_RETURN(HA_ERR_OUT_OF_MEM);
@@ -180,29 +193,20 @@ int xpand_connection::connect()
   }
 #endif
 
+  int error_code = 0;
   if (!mysql_real_connect(&xpand_net, host, xpand_username, xpand_password,
                           NULL, xpand_port, xpand_socket,
                           CLIENT_MULTI_STATEMENTS))
   {
     error_code = mysql_errno(&xpand_net);
     disconnect();
-
-    if (error_code != CR_CONN_HOST_ERROR &&
-        error_code != CR_CONNECTION_ERROR)
-    {
-      if (error_code == ER_CON_COUNT_ERROR)
-      {
-        my_error(ER_CON_COUNT_ERROR, MYF(0));
-        DBUG_RETURN(ER_CON_COUNT_ERROR);
-      }
-      my_error(ER_CONNECT_TO_FOREIGN_DATA_SOURCE, MYF(0), host);
-      DBUG_RETURN(ER_CONNECT_TO_FOREIGN_DATA_SOURCE);
-    }
   }
 
-  xpand_net.reconnect = 1;
+  if (error_code && error_code != ER_CON_COUNT_ERROR) {
+    error_code = ER_CONNECT_TO_FOREIGN_DATA_SOURCE;
+  }
 
-  DBUG_RETURN(0);
+  DBUG_RETURN(error_code);
 }
 
 int xpand_connection::add_status_vars()
@@ -1268,3 +1272,69 @@ int xpand_connection::add_command_operand_bitmap(MY_BITMAP *bitmap)
   command_length += no_bytes;
   return 0;
 }
+
+/****************************************************************************
+** Class xpand_host_list
+****************************************************************************/
+
+xpand_host_list *xpand_host_list::create(const char *hosts, int *error_code)
+{
+  return xpand_host_list::create(hosts, NULL, error_code);
+}
+
+xpand_host_list *xpand_host_list::create(const char *hosts, THD *thd, int *error_code)
+{
+  xpand_host_list *list = static_cast<xpand_host_list*>(
+                          thd ?
+                          thd_calloc(thd, sizeof(xpand_host_list)) :
+                          my_malloc(sizeof(xpand_host_list), MYF(MY_WME | MY_ZEROFILL)));
+  if (!list) {
+    *error_code = HA_ERR_OUT_OF_MEM;
+    return NULL;
+  }
+
+  list->full_list = thd ?
+                    thd_strdup(thd, hosts) :
+                    my_strdup(hosts, MYF(MY_WME));
+  list->strtok_buf = thd ?
+                     thd_strdup(thd, hosts) :
+                     my_strdup(hosts, MYF(MY_WME));
+  if (!list->full_list || !list->strtok_buf) {
+    *error_code = HA_ERR_OUT_OF_MEM;
+    return NULL;
+  }
+
+  const char *sep = ",; ";
+  //parse into array
+  int i = 0;
+  char *cursor = NULL;
+  char *token = NULL;
+  for (token = strtok_r(list->strtok_buf, sep, &cursor);
+       token && i < max_host_count;
+       token = strtok_r(NULL, sep, &cursor)) {
+    list->hosts[i] = token;
+    i++;
+  }
+
+  //host count out of range
+  if (i == 0 || token) {
+    my_free(list->full_list);
+    my_free(list->strtok_buf);
+    my_free(list);
+    *error_code = ER_BAD_HOST_ERROR;
+    return NULL;
+  }
+  list->hosts_len = i;
+
+  return list;
+}
+
+void xpand_host_list::operator delete(void *p)
+{
+  xpand_host_list *list = static_cast<xpand_host_list*>(p);
+  if (list) {
+    my_free(list->full_list);
+    my_free(list->strtok_buf);
+  }
+  my_free(list);
+}

storage/xpand/xpand_connection.h

@@ -21,11 +21,32 @@ Copyright (c) 2019, MariaDB Corporation.
 
 #define XPAND_SERVER_REQUEST 30
 
-typedef enum xpand_lock_mode {
+enum xpand_lock_mode_t {
     XPAND_NO_LOCKS,
     XPAND_SHARED,
     XPAND_EXCLUSIVE,
-} xpand_lock_mode_t;
+};
+
+enum xpand_balance_algorithm_enum {
+  XPAND_BALANCE_FIRST,
+  XPAND_BALANCE_ROUND_ROBIN
+};
+
+static const int max_host_count = 128;
+class xpand_host_list {
+private:
+  char *strtok_buf;
+public:
+  char *full_list;
+  int hosts_len;
+  char *hosts[max_host_count];
+
+  static xpand_host_list *create(const char *hosts, int *error_code);
+  static xpand_host_list *create(const char *hosts, THD *thd, int *error_code);
+  xpand_host_list() = delete;
+  static void operator delete(void *p);
+};
+
 
 class xpand_connection_cursor;
 class xpand_connection
@@ -50,6 +71,7 @@ class xpand_connection
     return xpand_net.net.vio;
   }
   int connect();
+  int connect_direct(char *host);
   void disconnect(bool is_destructor = FALSE);
 
   bool has_open_transaction();