MDEV-18702 mysqldump: add variable 'max-statement-time'

With a global non-default max-statement-time of a time interval that exceed
the query time mysqldump queries when doing a backup.

To solve both, add a max-statement-time option, defaulting to 0 (unlimited time).

Also like mariabackup, set the session wait_timeout=DEFAULT (28800). The
time/processing between mysqldump times isn't expected to get that
close ever, but let's adopt the standard of mariabackup as no-one has
challenged it has having a detrimental effect.

Reviewer and test case author Daniel Black

client/mysqldump.c

@@ -146,6 +146,7 @@ static ulonglong opt_system= 0ULL;
 static my_bool insert_pat_inited= 0, debug_info_flag= 0, debug_check_flag= 0,
                select_field_names_inited= 0;
 static ulong opt_max_allowed_packet, opt_net_buffer_length;
+static double opt_max_statement_time= 0.0;
 static MYSQL mysql_connection,*mysql=0;
 static DYNAMIC_STRING insert_pat, select_field_names;
 static char  *opt_password=0,*current_user=0,
@@ -162,6 +163,7 @@ static my_bool server_supports_switching_charsets= TRUE;
 static ulong opt_compatible_mode= 0;
 #define MYSQL_OPT_MASTER_DATA_EFFECTIVE_SQL 1
 #define MYSQL_OPT_MASTER_DATA_COMMENTED_SQL 2
+#define MYSQL_OPT_MAX_STATEMENT_TIME 0
 #define MYSQL_OPT_SLAVE_DATA_EFFECTIVE_SQL 1
 #define MYSQL_OPT_SLAVE_DATA_COMMENTED_SQL 2
 static uint opt_mysql_port= 0, opt_master_data;
@@ -464,6 +466,10 @@ static struct my_option my_long_options[] =
     &opt_max_allowed_packet, &opt_max_allowed_packet, 0,
     GET_ULONG, REQUIRED_ARG, 24*1024*1024, 4096,
    (longlong) 2L*1024L*1024L*1024L, MALLOC_OVERHEAD, 1024, 0},
+  {"max-statement-time", MYSQL_OPT_MAX_STATEMENT_TIME,
+   "Max statement execution time. If unset, overrides server default with 0.",
+   &opt_max_statement_time, &opt_max_statement_time, 0, GET_DOUBLE,
+   REQUIRED_ARG, 0, 0, 0, 0, 0, 0},
   {"net_buffer_length", OPT_NET_BUFFER_LENGTH, 
    "The buffer size for TCP/IP and socket communication.",
     &opt_net_buffer_length, &opt_net_buffer_length, 0,
@@ -6816,6 +6822,7 @@ static void dynstr_realloc_checked(DYNAMIC_STRING *str, ulong additional_size)
 
 int main(int argc, char **argv)
 {
+  char query[48];
   char bin_log_name[FN_REFLEN];
   int exit_code;
   int consistent_binlog_pos= 0;
@@ -6857,6 +6864,13 @@ int main(int argc, char **argv)
   if (!path)
     write_header(md_result_file, *argv);
 
+  /* Set MAX_STATEMENT_TIME to 0 unless set in client */
+  my_snprintf(query, sizeof(query), "/*!100100 SET @@MAX_STATEMENT_TIME=%f */", opt_max_statement_time);
+  mysql_query(mysql, query);
+
+  /* Set server side timeout between client commands to server compiled-in default */
+  mysql_query(mysql, "/*!100100 SET WAIT_TIMEOUT=DEFAULT */");
+
   /* Check if the server support multi source */
   if (mysql_get_server_version(mysql) >= 100000)
   {

man/mysqldump.1

@@ -1361,6 +1361,21 @@ Sets the maximum packet length to send to or receive from server\&.
 .sp -1
 .IP \(bu 2.3
 .\}
+.\" mysqldump: max-statement-time option
+.\" max-statement-time option: mysqldump
+\fB\-\-max\-statement\-time=\fR\fB\fIseconds\fR\fR
+.sp
+Sets the maximum time any statement can run before being timed out by the server. (Default value is 0 (no limit))\&
+.RE
+.sp
+.RS 4
+.ie n \{\
+\h'-04'\(bu\h'+03'\c
+.\}
+.el \{\
+.sp -1
+.IP \(bu 2.3
+.\}
 .\" mysqldump: net-buffer-length option
 .\" net-buffer-length option: mysqldump
 \fB\-\-net\-buffer\-length=\fR\fB\fIlength\fR\fR
@@ -2619,6 +2634,21 @@ The maximum size of the buffer for client/server communication\&. The maximum is
 .sp -1
 .IP \(bu 2.3
 .\}
+max_statement_time
+.sp
+A query that has taken more than max_statement_time seconds will be aborted and the backup will
+fail\&. The argument will be treated as a decimal value with microsecond precision\&. A value
+of 0 (default) means no timeout\&. The maximum timeout is 31536000 seconds\&.
+.RE
+.sp
+.RS 4
+.ie n \{\
+\h'-04'\(bu\h'+03'\c
+.\}
+.el \{\
+.sp -1
+.IP \(bu 2.3
+.\}
 net_buffer_length
 .sp
 The initial size of the buffer for client/server communication\&. When creating multiple\-row

mysql-test/main/mysqldump-timing.result

@@ -0,0 +1,71 @@
+#
+# MDEV-18702 mysqldump should use max_statement_time=0 and/or allow setting one
+#
+CREATE DATABASE test1;
+USE test1;
+CREATE TABLE t1 (i INT);
+INSERT INTO t1 VALUES (0);
+LOCK TABLE t1 WRITE;
+timeout without t1 contents expected
+
+/*!40101 SET @OLD_CHARACTER_SET_CLIENT=@@CHARACTER_SET_CLIENT */;
+/*!40101 SET @OLD_CHARACTER_SET_RESULTS=@@CHARACTER_SET_RESULTS */;
+/*!40101 SET @OLD_COLLATION_CONNECTION=@@COLLATION_CONNECTION */;
+/*!40101 SET NAMES utf8mb4 */;
+/*!40103 SET @OLD_TIME_ZONE=@@TIME_ZONE */;
+/*!40103 SET TIME_ZONE='+00:00' */;
+/*!40014 SET @OLD_UNIQUE_CHECKS=@@UNIQUE_CHECKS, UNIQUE_CHECKS=0 */;
+/*!40014 SET @OLD_FOREIGN_KEY_CHECKS=@@FOREIGN_KEY_CHECKS, FOREIGN_KEY_CHECKS=0 */;
+/*!40101 SET @OLD_SQL_MODE=@@SQL_MODE, SQL_MODE='NO_AUTO_VALUE_ON_ZERO' */;
+/*!40111 SET @OLD_SQL_NOTES=@@SQL_NOTES, SQL_NOTES=0 */;
+DROP TABLE IF EXISTS `t1`;
+/*!40101 SET @saved_cs_client     = @@character_set_client */;
+/*!40101 SET character_set_client = utf8 */;
+CREATE TABLE `t1` (
+  `i` int(11) DEFAULT NULL
+) ENGINE=MyISAM DEFAULT CHARSET=latin1;
+/*!40101 SET character_set_client = @saved_cs_client */;
+
+SET @save_max_statement_time=@@max_statement_time;
+SET GLOBAL max_statement_time=0.1;
+UNLOCK TABLES;;
+This would be a race condition otherwise, but default max_statement_time=0 makes it succeed
+
+/*!40101 SET @OLD_CHARACTER_SET_CLIENT=@@CHARACTER_SET_CLIENT */;
+/*!40101 SET @OLD_CHARACTER_SET_RESULTS=@@CHARACTER_SET_RESULTS */;
+/*!40101 SET @OLD_COLLATION_CONNECTION=@@COLLATION_CONNECTION */;
+/*!40101 SET NAMES utf8mb4 */;
+/*!40103 SET @OLD_TIME_ZONE=@@TIME_ZONE */;
+/*!40103 SET TIME_ZONE='+00:00' */;
+/*!40014 SET @OLD_UNIQUE_CHECKS=@@UNIQUE_CHECKS, UNIQUE_CHECKS=0 */;
+/*!40014 SET @OLD_FOREIGN_KEY_CHECKS=@@FOREIGN_KEY_CHECKS, FOREIGN_KEY_CHECKS=0 */;
+/*!40101 SET @OLD_SQL_MODE=@@SQL_MODE, SQL_MODE='NO_AUTO_VALUE_ON_ZERO' */;
+/*!40111 SET @OLD_SQL_NOTES=@@SQL_NOTES, SQL_NOTES=0 */;
+DROP TABLE IF EXISTS `t1`;
+/*!40101 SET @saved_cs_client     = @@character_set_client */;
+/*!40101 SET character_set_client = utf8 */;
+CREATE TABLE `t1` (
+  `i` int(11) DEFAULT NULL
+) ENGINE=MyISAM DEFAULT CHARSET=latin1;
+/*!40101 SET character_set_client = @saved_cs_client */;
+
+LOCK TABLES `t1` WRITE;
+/*!40000 ALTER TABLE `t1` DISABLE KEYS */;
+INSERT INTO `t1` VALUES (0);
+/*!40000 ALTER TABLE `t1` ENABLE KEYS */;
+UNLOCK TABLES;
+/*!40103 SET TIME_ZONE=@OLD_TIME_ZONE */;
+
+/*!40101 SET SQL_MODE=@OLD_SQL_MODE */;
+/*!40014 SET FOREIGN_KEY_CHECKS=@OLD_FOREIGN_KEY_CHECKS */;
+/*!40014 SET UNIQUE_CHECKS=@OLD_UNIQUE_CHECKS */;
+/*!40101 SET CHARACTER_SET_CLIENT=@OLD_CHARACTER_SET_CLIENT */;
+/*!40101 SET CHARACTER_SET_RESULTS=@OLD_CHARACTER_SET_RESULTS */;
+/*!40101 SET COLLATION_CONNECTION=@OLD_COLLATION_CONNECTION */;
+/*!40111 SET SQL_NOTES=@OLD_SQL_NOTES */;
+
+SET GLOBAL max_statement_time=@save_max_statement_time;
+DROP DATABASE test1;
+#
+# End of 10.3 test
+#

mysql-test/main/mysqldump-timing.test

@@ -0,0 +1,26 @@
+
+
+--echo #
+--echo # MDEV-18702 mysqldump should use max_statement_time=0 and/or allow setting one
+--echo #
+
+CREATE DATABASE test1;
+USE test1;
+CREATE TABLE t1 (i INT);
+INSERT INTO t1 VALUES (0);
+LOCK TABLE t1 WRITE;
+--echo timeout without t1 contents expected
+--error 2
+--exec $MYSQL_DUMP --max-statement-time=1 --skip-lock-tables --skip-comments test1 t1
+SET @save_max_statement_time=@@max_statement_time;
+SET GLOBAL max_statement_time=0.1;
+--send UNLOCK TABLES;
+--echo This would be a race condition otherwise, but default max_statement_time=0 makes it succeed
+--exec $MYSQL_DUMP --skip-lock-tables --skip-comments test1 t1
+--reap
+SET GLOBAL max_statement_time=@save_max_statement_time;
+DROP DATABASE test1;
+
+--echo #
+--echo # End of 10.3 test
+--echo #