enhancement:does it support aliyun rds?

[dikang123]

aliyun rds is a version of amazon rds in China:aliyun rds.

I have a test,but return some sort of error:
2017-08-15 16:40:38 FATAL sql: Scan error on column index 0: converting driver.Value type <nil> ("<nil>") to a int: invalid syntax

[shlomi-noach]

@dikang123 any more input is appreciated. What is the table you're trying to convert? Which mysql version? Which gh-ost version? What's the alter statement?

[dikang123]

original table structure:

CREATE TABLE `vote_record` (
  `id` bigint(20) unsigned NOT NULL AUTO_INCREMENT COMMENT '主键id',
  `user_id` varchar(22) DEFAULT NULL,
  `vote_num` int(10) unsigned NOT NULL DEFAULT '0' COMMENT '投票数',
  `group_id` int(10) unsigned NOT NULL DEFAULT '0' COMMENT '用户组id 0-未激活用户 1-普通用户 2-vip用户 3-管理员用户',
  `status` tinyint(2) unsigned NOT NULL DEFAULT '1' COMMENT '状态 1-正常 2-已删除',
  `create_time` datetime NOT NULL DEFAULT '0000-00-00 00:00:00' COMMENT '创建时间',
  `modify_time` datetime NOT NULL DEFAULT CURRENT_TIMESTAMP ON UPDATE CURRENT_TIMESTAMP,
  `col2` bigint(20) DEFAULT NULL COMMENT 'test',
  PRIMARY KEY (`id`),
  UNIQUE KEY `udx_user_id` (`user_id`),
  KEY `idx_usr_id` (`user_id`)
) ENGINE=InnoDB AUTO_INCREMENT=200000 DEFAULT CHARSET=utf8 COMMENT='投票记录表'；

mysql version:5.6.16-log
gh-ost:1.0.40

alter statement:

./gh-ost --host=xxx --user=xxx --password=xxx --database=appversionsdb --table=vote_record --alter="add column tag int not null default 0" --chunk-size=2000 --max-load=Threads_running=20 --allow-on-master --execute

[shlomi-noach]

@dikang123 can I get the log preceeding that fatal message please?

@siddontang do you have any insight into aliyun rds?

[dikang123]

@shlomi-noach the only thing I got after typing the command was the error:

FATAL sql: Scan error on column index 0: converting driver.Value type <nil> ("<nil>") to a int: invalid syntax

is there some sort of debug mode?

[shlomi-noach]

@dikang123 please run with --debug --stack

[siddontang]

Hi @shlomi-noach

I have not used Aliyun RDS before. We should know the executing query which causes the panic.

[dikang123]

@shlomi-noach
the output:

2017-08-18 11:37:28 INFO starting gh-ost 1.0.40
2017-08-18 11:37:28 INFO Migrating `appversionsdb`.`vote_record`
2017-08-18 11:37:28 FATAL sql: Scan error on column index 0: converting driver.Value type <nil> ("<nil>") to a int: invalid syntax
goroutine 1 [running]:
runtime/debug.Stack(0x82, 0x68, 0x0)
	/usr/local/Cellar/go/1.8.3/libexec/src/runtime/debug/stack.go:24 +0x79
runtime/debug.PrintStack()
	/usr/local/Cellar/go/1.8.3/libexec/src/runtime/debug/stack.go:16 +0x22
github.com/github/gh-ost/vendor/github.com/outbrain/golib/log.logErrorEntry(0x0, 0x8f8a80, 0xc42016a160, 0x0, 0x0)
	/Users/shlomi-noach/dev/go/src/github.com/github/gh-ost/vendor/github.com/outbrain/golib/log/log.go:178 +0xfd
github.com/github/gh-ost/vendor/github.com/outbrain/golib/log.Fatale(0x8f8a80, 0xc42016a160, 0x0, 0x0)
	/Users/shlomi-noach/dev/go/src/github.com/github/gh-ost/vendor/github.com/outbrain/golib/log/log.go:255 +0x3e
main.main()
	/Users/shlomi-noach/dev/go/src/github.com/github/gh-ost/go/cmd/gh-ost/main.go:247 +0x1d3b

[shlomi-noach]

pro tip: use three backticks for multi line code formatting. See how I've edited your comment.

[shlomi-noach]

@siddontang not even you code -- thank you!

[shlomi-noach]

@dikang123 the error is with reading nil (or a database NULL value) into a variable via go-mysql-driver.

The error message unfortunately doesn't make it clear where this happened exactly, but by elimination I suspect this is the result of executing select @@global.port, @@global.version. Can you verify that the gh-ost user you're using can run this query? What's the output for the query?

[dikang123]

@shlomi-noach
[root@proxy ~]# mysql -uxxx -pxxx -hxxx -e "select @@global.port"
+---------------+
| @@global.port |
+---------------+
| NULL |
+---------------+

seems like the port is NULL !

[root@proxy ~]# mysql -uxxx -pxxx-hxxx-e "select @@global.version"
+------------------+
| @@global.version |
+------------------+
| 5.6.16-log |
+------------------+

[shlomi-noach]

@dikang123 thank you. Your task is to find out why select @@global.port is NULL. This shouldn't happen, and I've never seen this happen before, never even considered this to be a possibility, and I assume this must be introduced behavior by aliyun. Can you look into it?

[dikang123]

@shlomi-noach yeah, I agree about that. There exists some limitations to make the global variable 'port' a null value! Is there some method to ignore or bypass this issue?

[shlomi-noach]

@dikang123, heh, you tell me 😄

If you can please run a quick investigation and let me know what aliyun does allow. Perhaps it allows select @@port? Perhaps another way to detect the port?

BTW, what is the output of show global variables like 'version%';?

[dikang123]

@shlomi-noach

mysql>show global variables like 'version%';
+-------------------------+---------------------+
| Variable_name           | Value               |
+-------------------------+---------------------+
| version                 | 5.6.16-log          |
| version_comment         | Source distribution |
| version_compile_machine | x86_64              |
| version_compile_os      | Linux               |
+-------------------------+---------------------+