MDEV-15712: If remote server used by Spider table is unavailable, some...

MDEV-15712: If remote server used by Spider table is unavailable, some operations hang for a long time

When an attempt to connect to the remote server fails, Spider retries to
connect to the remote server 1000 times or until the connection attempt
succeeds.  This is perceived as a hang if the remote server remains
unavailable.

I have introduced changes in Spider's table status handler to fix this problem.

Author:
  Jacob Mathew.

Reviewer:
  Kentoku Shiba.

storage/spider/spd_db_conn.cc

@@ -121,7 +121,10 @@ int spider_db_connect(
     conn->net_write_timeout = spider_param_net_write_timeout(thd,
       share->net_write_timeouts[link_idx]);
     connect_retry_interval = spider_param_connect_retry_interval(thd);
-    connect_retry_count = spider_param_connect_retry_count(thd);
+    if (conn->disable_connect_retry)
+      connect_retry_count = 0;
+    else
+      connect_retry_count = spider_param_connect_retry_count(thd);
   } else {
     conn->connect_timeout = spider_param_connect_timeout(NULL,
       share->connect_timeouts[link_idx]);

storage/spider/spd_db_mysql.cc

@@ -11139,6 +11139,7 @@ int spider_mysql_handler::show_table_status(
   ulonglong auto_increment_value = 0;
   DBUG_ENTER("spider_mysql_handler::show_table_status");
   DBUG_PRINT("info",("spider sts_mode=%d", sts_mode));
+
   if (sts_mode == 1)
   {
     pthread_mutex_lock(&conn->mta_conn_mutex);
@@ -11146,6 +11147,7 @@ int spider_mysql_handler::show_table_status(
     conn->need_mon = &spider->need_mons[link_idx];
     conn->mta_conn_mutex_lock_already = TRUE;
     conn->mta_conn_mutex_unlock_later = TRUE;
+    conn->disable_connect_retry = TRUE;
     spider_conn_set_timeout_from_share(conn, link_idx, spider->trx->thd,
       share);
     if (
@@ -11167,6 +11169,7 @@ int spider_mysql_handler::show_table_status(
         /* retry */
         if ((error_num = spider_db_ping(spider, conn, link_idx)))
         {
+          conn->disable_connect_retry = FALSE;
           conn->mta_conn_mutex_lock_already = FALSE;
           conn->mta_conn_mutex_unlock_later = FALSE;
           SPIDER_CLEAR_FILE_POS(&conn->mta_conn_mutex_file_pos);
@@ -11175,6 +11178,7 @@ int spider_mysql_handler::show_table_status(
         }
         if ((error_num = spider_db_set_names(spider, conn, link_idx)))
         {
+          conn->disable_connect_retry = FALSE;
           conn->mta_conn_mutex_lock_already = FALSE;
           conn->mta_conn_mutex_unlock_later = FALSE;
           SPIDER_CLEAR_FILE_POS(&conn->mta_conn_mutex_file_pos);
@@ -11190,11 +11194,13 @@ int spider_mysql_handler::show_table_status(
           -1,
           &spider->need_mons[link_idx])
         ) {
+          conn->disable_connect_retry = FALSE;
           conn->mta_conn_mutex_lock_already = FALSE;
           conn->mta_conn_mutex_unlock_later = FALSE;
           DBUG_RETURN(spider_db_errorno(conn));
         }
       } else {
+        conn->disable_connect_retry = FALSE;
         conn->mta_conn_mutex_lock_already = FALSE;
         conn->mta_conn_mutex_unlock_later = FALSE;
         SPIDER_CLEAR_FILE_POS(&conn->mta_conn_mutex_file_pos);
@@ -11210,6 +11216,7 @@ int spider_mysql_handler::show_table_status(
     request_key.next = NULL;
     if (spider_param_dry_access())
     {
+      conn->disable_connect_retry = FALSE;
       conn->mta_conn_mutex_lock_already = FALSE;
       conn->mta_conn_mutex_unlock_later = FALSE;
       SPIDER_CLEAR_FILE_POS(&conn->mta_conn_mutex_file_pos);
@@ -11218,11 +11225,13 @@ int spider_mysql_handler::show_table_status(
     }
     if (!(res = conn->db_conn->store_result(NULL, &request_key, &error_num)))
     {
+      conn->disable_connect_retry = FALSE;
       conn->mta_conn_mutex_lock_already = FALSE;
       conn->mta_conn_mutex_unlock_later = FALSE;
       if (error_num || (error_num = spider_db_errorno(conn)))
         DBUG_RETURN(error_num);
-      else {
+      else
+      {
         my_printf_error(ER_SPIDER_REMOTE_TABLE_NOT_FOUND_NUM,
           ER_SPIDER_REMOTE_TABLE_NOT_FOUND_STR, MYF(0),
           mysql_share->db_names_str[spider->conn_link_idx[link_idx]].ptr(),
@@ -11231,6 +11240,7 @@ int spider_mysql_handler::show_table_status(
         DBUG_RETURN(ER_SPIDER_REMOTE_TABLE_NOT_FOUND_NUM);
       }
     }
+    conn->disable_connect_retry = FALSE;
     conn->mta_conn_mutex_lock_already = FALSE;
     conn->mta_conn_mutex_unlock_later = FALSE;
     SPIDER_CLEAR_FILE_POS(&conn->mta_conn_mutex_file_pos);
@@ -11278,6 +11288,7 @@ int spider_mysql_handler::show_table_status(
     conn->need_mon = &spider->need_mons[link_idx];
     conn->mta_conn_mutex_lock_already = TRUE;
     conn->mta_conn_mutex_unlock_later = TRUE;
+    conn->disable_connect_retry = TRUE;
     spider_conn_set_timeout_from_share(conn, link_idx, spider->trx->thd,
       share);
     if (
@@ -11299,6 +11310,7 @@ int spider_mysql_handler::show_table_status(
         /* retry */
         if ((error_num = spider_db_ping(spider, conn, link_idx)))
         {
+          conn->disable_connect_retry = FALSE;
           conn->mta_conn_mutex_lock_already = FALSE;
           conn->mta_conn_mutex_unlock_later = FALSE;
           SPIDER_CLEAR_FILE_POS(&conn->mta_conn_mutex_file_pos);
@@ -11307,6 +11319,7 @@ int spider_mysql_handler::show_table_status(
         }
         if ((error_num = spider_db_set_names(spider, conn, link_idx)))
         {
+          conn->disable_connect_retry = FALSE;
           conn->mta_conn_mutex_lock_already = FALSE;
           conn->mta_conn_mutex_unlock_later = FALSE;
           SPIDER_CLEAR_FILE_POS(&conn->mta_conn_mutex_file_pos);
@@ -11322,11 +11335,13 @@ int spider_mysql_handler::show_table_status(
           -1,
           &spider->need_mons[link_idx])
         ) {
+          conn->disable_connect_retry = FALSE;
           conn->mta_conn_mutex_lock_already = FALSE;
           conn->mta_conn_mutex_unlock_later = FALSE;
           DBUG_RETURN(spider_db_errorno(conn));
         }
       } else {
+        conn->disable_connect_retry = FALSE;
         conn->mta_conn_mutex_lock_already = FALSE;
         conn->mta_conn_mutex_unlock_later = FALSE;
         SPIDER_CLEAR_FILE_POS(&conn->mta_conn_mutex_file_pos);
@@ -11342,6 +11357,7 @@ int spider_mysql_handler::show_table_status(
     request_key.next = NULL;
     if (spider_param_dry_access())
     {
+      conn->disable_connect_retry = FALSE;
       conn->mta_conn_mutex_lock_already = FALSE;
       conn->mta_conn_mutex_unlock_later = FALSE;
       SPIDER_CLEAR_FILE_POS(&conn->mta_conn_mutex_file_pos);
@@ -11350,6 +11366,7 @@ int spider_mysql_handler::show_table_status(
     }
     if (!(res = conn->db_conn->store_result(NULL, &request_key, &error_num)))
     {
+      conn->disable_connect_retry = FALSE;
       conn->mta_conn_mutex_lock_already = FALSE;
       conn->mta_conn_mutex_unlock_later = FALSE;
       if (error_num || (error_num = spider_db_errorno(conn)))
@@ -11357,6 +11374,7 @@ int spider_mysql_handler::show_table_status(
       else
         DBUG_RETURN(ER_QUERY_ON_FOREIGN_DATA_SOURCE);
     }
+    conn->disable_connect_retry = FALSE;
     conn->mta_conn_mutex_lock_already = FALSE;
     conn->mta_conn_mutex_unlock_later = FALSE;
     SPIDER_CLEAR_FILE_POS(&conn->mta_conn_mutex_file_pos);
@@ -11413,6 +11431,7 @@ int spider_mysql_handler::show_table_status(
     DBUG_PRINT("info",("spider auto_increment_value=%llu",
       share->lgtm_tblhnd_share->auto_increment_value));
   }
+
   DBUG_RETURN(0);
 }
 

storage/spider/spd_include.h

@@ -526,6 +526,9 @@ typedef struct st_spider_conn
   st_spider_conn     *bulk_access_next;
 #endif
 
+  bool               disable_connect_retry;  /* TRUE if it is unnecessary to
+                                                retry to connect after a
+                                                connection error */
   bool               connect_error_with_message;
   char               connect_error_msg[MYSQL_ERRMSG_SIZE];
   int                connect_error;