Openwrt上mysql innodb的使用及相关异常情况

        首先在menuconfig中配置mysql，具体是在Utilities->database->mysql-server。这样直接编译就可以了，不过这样默认是不支持innodb存储引擎的，估计是考虑openwrt一般是运行的硬件有关，不需要这么复杂的存储引擎（占用空间也比MyISAM存储引擎大）。但是，如果需要支持innodb存储引擎该怎么办？这类型的网上帖子不多，我是之前参照国外的论坛加自己测试得出的。

Openwrt支持innodb存储引擎
修改feeds/oldpackages/libs/mysql/Makefile
在--with-server之前加--with-innodb

修改feeds/oldpackages/libs/mysql/conf/my.cnf
在[mysqld]中加default-storage-engine=INNODB
在bind-address = 127.0.0.1下载添加
innodb
innodb_file_per_table = 1
innodb_flush_log_at_trx_commit = 2

/etc/init.d/mysqld脚本start函数中添加

start() {
	local datadir=$(sed -n -e "s/^[[:space:]]*datadir[[:space:]]*=[[:space:]]*[\"']\?\([^\"']*\)[\"']\?/\1/p" /etc/my.cnf)
	local mysqldatadir="/mnt/data/mysql/"
        local mysqltmpdir="/mnt/data/tmp/"
	local mysqlsrvdir="/srv/mysql/"
        if [ ! -d "$mysqldatadir" ]; then
                echo "create dir /mnt/data/mysql/..."
                mkdir -p "$mysqldatadir"
        fi
        if [ ! -d "$mysqltmpdir" ]; then            
		echo "create dir /mnt/data/tmp/..."
		mkdir -p "$mysqltmpdir"
	fi
	if [ ! -d "$mysqlsrvdir" ]; then            
		echo "create dir /srv/mysql/..."
		mkdir -p "$mysqlsrvdir"
	fi
	if [ ! -d "$datadir" ]; then
		error "Error: datadir '$datadir' in /etc/my.cnf doesn't exist"
		return 1
	fi
	if [ ! -f "$datadir/mysql/tables_priv.MYD" ]; then
		mysql_install_db --force
		service_stop /usr/bin/mysqld
		#error "Error: I didn't detect a privileges table, you might need to run mysql_install_db --force to initialize the system tables"
		#return 1
	fi
	service_start /usr/bin/mysqld
}

        至此，基于innodb的MySQL就可以正常运行了。
        在基于netgear3700v2硬件的openwrt上，会出现初始化innodb的情况，异常表现为创建socket失败，提示如Can‘t connect to local MySQL server through socket ‘/var/run/mysqld/mysqld.sock‘。其实这个是因为初始化innodb失败造成的，因为netgear3700v2的flash只有16M，不能满足innodb的运行需求，数据文件大小总和至少要达到 10 MB。通过敲入mysqld --skip-grant&命令可能会打印出类似如下的信息：
root@BDCOM_AP:/# mysqld --skip-grant&
root@BDCOM_AP:/# 150203  1:32:31  InnoDB: Initializing buffer pool, size = 8.0M
150203  1:32:31  InnoDB: Completed initialization of buffer pool
InnoDB: Error: auto-extending data file ./ibdata1 is of a different size
InnoDB: 64 pages (rounded down to MB) than specified in the .cnf file:
InnoDB: initial 640 pages, max 0 (relevant if non-zero) pages!
InnoDB: Could not open or create data files.
InnoDB: If you tried to add new data files, and it failed here,
InnoDB: you should now edit innodb_data_file_path in my.cnf back
InnoDB: to what it was, and remove the new ibdata files InnoDB created
InnoDB: in this failed attempt. InnoDB only wrote those files full of
InnoDB: zeros, but did not yet use them in any way. But be careful: do not
InnoDB: remove old data files which contain your precious data!
150203  1:32:31 [ERROR] Plugin ‘InnoDB‘ init function returned error.
150203  1:32:31 [ERROR] Plugin ‘InnoDB‘ registration as a STORAGE ENGINE failed.
150203  1:32:31 [ERROR] Unknown/unsupported table type: INNODB
150203  1:32:31 [ERROR] Aborting

150203  1:32:31 [Note] mysqld: Shutdown complete

        上述这个莫名其妙的问题经过验证确实是由于flash空间不够引起的。解决的办法是，在路由器上挂载一个U盘。挂载U盘的配置项为：
kernel modules ->filesystems->kmod-fs-vfat
kernel modules->native language support->kmod-nls-cp437/kmod-nls-iso8859-1/kmod-nls-utf-8
kernel modules->usb support->kmod-usb-core/kmod-usb-ohci/kmod-usb-storage/kmod-usb-usb2
。
     还有，在init初始化脚本中如果顺序执行多个mysql操作的时候，如mysql_install_db --force命令之后接着mysqladmin -u root password ‘123456‘则可能会失败，因为还没等mysql_install_db执行完成就会执行mysqladmin命令。解决此问题的办法是加sleep时间，具体多长时间可以视情况而定。