MySQL 5.6 Replication.txt

MySQL 5.6引入的GTID(Global Transaction IDs)使得其复制功能的配置、监控及管理变得更加易于实现，且更加健壮。

要在MySQL 5.6中使用复制功能，其服务配置段[mysqld]中于少应该定义如下选项：

binlog-format：二进制日志的格式，有row、statement和mixed几种类型；
	需要注意的是：当设置隔离级别为READ-COMMITED必须设置二进制日志格式为ROW，现在MySQL官方认为STATEMENT这个已经不再适合继续使用；但mixed类型在默认的事务隔离级别下，可能会导致主从数据不一致；
log-slave-updates、gtid-mode、enforce-gtid-consistency、report-port和report-host：用于启动GTID及满足附属的其它需求；
master-info-repository和relay-log-info-repository：启用此两项，可用于实现在崩溃时保证二进制及从服务器安全的功能；
sync-master-info：启用之可确保无信息丢失；
slave-paralles-workers：设定从服务器的SQL线程数；0表示关闭多线程复制功能；
binlog-checksum、master-verify-checksum和slave-sql-verify-checksum：启用复制有关的所有校验功能；
binlog-rows-query-log-events：启用之可用于在二进制日志记录事件相关的信息，可降低故障排除的复杂度；
log-bin：启用二进制日志，这是保证复制功能的基本前提；
server-id：同一个复制拓扑中的所有服务器的id号必须惟一；


report-host：
The host name or IP address of the slave to be reported to the master during slave registration. This value appears in the output of SHOW SLAVE HOSTS on the master server.

report-port:
The TCP/IP port number for connecting to the slave, to be reported to the master during slave registration.

master-info-repository:
The setting of this variable determines whether the slave logs master status and connection information to a FILE (master.info), or to a TABLE (mysql.slave_master_info)

relay-log-info-repository：
This option causes the server to log its relay log info to a file or a table.

log_slave_updates：
Whether updates received by a slave server from a master server should be logged to the slave's own binary log. Binary logging must be enabled on the slave for this variable to have any effect. 

 enforce_gtid_consistency：




一、简单主从模式配置步骤

1、配置主从节点的服务配置文件

1.1、配置master节点：
[mysqld]
binlog-format=ROW
log-bin=master-bin
log-slave-updates=true
gtid-mode=on 
enforce-gtid-consistency=true
master-info-repository=TABLE
relay-log-info-repository=TABLE
sync-master-info=1
slave-parallel-workers=2
binlog-checksum=CRC32
master-verify-checksum=1
slave-sql-verify-checksum=1
binlog-rows-query-log_events=1
server-id=1
report-port=3306
port=3306
datadir=/mydata/data
socket=/tmp/mysql.sock
report-host=master.magedu.com

1.2、配置slave节点：
[mysqld]
binlog-format=ROW
log-slave-updates=true
gtid-mode=on 
enforce-gtid-consistency=true
master-info-repository=TABLE
relay-log-info-repository=TABLE
sync-master-info=1
slave-parallel-workers=2
binlog-checksum=CRC32
master-verify-checksum=1
slave-sql-verify-checksum=1
binlog-rows-query-log_events=1
server-id=11
report-port=3306
port=3306
log-bin=mysql-bin.log
datadir=/mydata/data
socket=/tmp/mysql.sock
report-host=slave.magedu.com

2、创建复制用户

mysql> GRANT REPLICATION SLAVE ON *.* TO repluser@172.16.100.7 IDENTIFIED BY 'replpass';

说明：172.16.100.7是从节点服务器；如果想一次性授权更多的节点，可以自行根据需要修改；

3、为备节点提供初始数据集

锁定主表，备份主节点上的数据，将其还原至从节点；如果没有启用GTID，在备份时需要在master上使用show master status命令查看二进制日志文件名称及事件位置，以便后面启动slave节点时使用。

4、启动从节点的复制线程

如果启用了GTID功能，则使用如下命令：
mysql> CHANGE MASTER TO MASTER_HOST='master.magedu.com', MASTER_USER='repluser', MASTER_PASSWORD='replpass', MASTER_AUTO_POSITION=1;

没启用GTID，需要使用如下命令：
slave> CHANGE MASTER TO MASTER_HOST='172.16.100.6',
-> MASTER_USER='repluser',
-> MASTER_PASSWORD='replpass',
-> MASTER_LOG_FILE='master-bin.000003',
-> MASTER_LOG_POS=1174;

二、半同步复制

1、分别在主从节点上安装相关的插件

master> INSTALL PLUGIN rpl_semi_sync_master SONAME 'semisync_master.so';
slave> INSTALL PLUGIN rpl_semi_sync_slave SONAME 'semisync_slave.so';

2、启用半同步复制

在master上的配置文件中，添加
rpl_semi_sync_master_enabled=ON

在至少一个slave节点的配置文件中添加
rpl_semi_sync_slave_enabled=ON

而后重新启动mysql服务即可生效。


或者，也可以mysql服务上动态启动其相关功能：

master> SET GLOBAL rpl_semi_sync_master_enabled = ON;
slave> SET GLOBAL rpl_semi_sync_slave_enabled = ON;
slave> STOP SLAVE IO_THREAD; START SLAVE IO_THREAD;

3、确认半同步功能已经启用

master> CREATE DATABASE magedudb;
master> SHOW STATUS LIKE 'Rpl_semi_sync_master_yes_tx';

slave> SHOW DATABASES; 




三、MySQL Proxy


1、源码安装时，MySQL proxy的依赖关系：

libevent 1.x or higher (1.3b or later is preferred).
lua 5.1.x or higher.
glib2 2.6.0 or higher.
pkg-config.
libtool 1.5 or higher.
MySQL 5.0.x or higher developer files.

2、安装

# tar zxf mysql-proxy-0.8.2.tar.gz
# cd mysql-proxy-0.8.2
# ./configure
# make

# make check

如果管理员有密码，上面的步骤则需要使用如下格式进行：
# MYSQL_PASSWORD=root_pwd make check

# make install

默认情况下， mysql-proxy安装在/usr/local/sbin/mysql-proxy，而Lua示例脚本安装在/usr/local/share目录中。

3、配置指令

mysql proxy的各配置参数请参见官方文档，http://dev.mysql.com/doc/refman/5.6/en/mysql-proxy-configuration.html






使用rpm包在rhel6上安装mysql-proxy-0.8.2，其会提供配置文件及服务脚本，但没有提供读写分享的脚本。


/etc/sysconfig/mysql-proxy文件用于定义mysql-proxy的启动参数。

ADMIN_USER – the user for the proxy's admin interface. You can leave the default admin user.
ADMIN_PASSWORD – the password for the admin user in clear text. Change the default password for better security.
ADMIN_LUA_SCRIPT – the admin script in the Lua programming language. Without this script the admin interface cannot work. You can leave the default value.
PROXY_USER – the system user under which the proxy will work. By default it is mysql-proxy, and it's safe to leave it as is.
PROXY_OPTIONS – proxy options such as logging level, plugins, and Lua scripts to be loaded.


其中PROXY_OPTIONS是最常用的一个选项，用于定义mysql-proxy工作时的重要参数，例如：
PROXY_OPTIONS="--daemon --log-level=info --log-use-syslog --plugins=proxy --plugins=admin --proxy-backend-addresses=192.168.1.102:3306 --proxy-read-only-backend-addresses=192.168.1.105:3306 --proxy-lua-script=/usr/lib/mysql-proxy/lua/proxy/rw-splitting.lua"











四、安装配置mysql-proxy:

4.1 下载所需要的版本，这里的系统平台为rhel6.4 32位系统，因此就以mysql-proxy-0.8.3-linux-glibc2.3-x86-32bit.tar.gz为例。

# tar xf mysql-proxy-0.8.3-linux-glibc2.3-x86-32bit.tar.gz -C /usr/local
# cd /usr/local
# ln -sv mysql-proxy-0.8.3-linux-glibc2.3-x86-32bit  mysql-proxy

添加代理用户
# useradd mysql-proxy

4.2 为mysql-proxy提供SysV服务脚本，内容如下所示

#!/bin/bash
#
# mysql-proxy This script starts and stops the mysql-proxy daemon
#
# chkconfig: - 78 30
# processname: mysql-proxy
# description: mysql-proxy is a proxy daemon for mysql

# Source function library.
. /etc/rc.d/init.d/functions

prog="/usr/local/mysql-proxy/bin/mysql-proxy"

# Source networking configuration.
if [ -f /etc/sysconfig/network ]; then
    . /etc/sysconfig/network
fi

# Check that networking is up.
[ ${NETWORKING} = "no" ] && exit 0

# Set default mysql-proxy configuration.
ADMIN_USER="admin"
ADMIN_PASSWD="admin"
ADMIN_LUA_SCRIPT="/usr/local/mysql-proxy/share/doc/mysql-proxy/admin.lua"
PROXY_OPTIONS="--daemon"
PROXY_PID=/var/run/mysql-proxy.pid
PROXY_USER="mysql-proxy"

# Source mysql-proxy configuration.
if [ -f /etc/sysconfig/mysql-proxy ]; then
    . /etc/sysconfig/mysql-proxy
fi

RETVAL=0

start() {
    echo -n $"Starting $prog: "
    daemon $prog $PROXY_OPTIONS --pid-file=$PROXY_PID --proxy-address="$PROXY_ADDRESS" --user=$PROXY_USER --admin-username="$ADMIN_USER" --admin-lua-script="$ADMIN_LUA_SCRIPT" --admin-password="$ADMIN_PASSWORD"
    RETVAL=$?
    echo
    if [ $RETVAL -eq 0 ]; then
        touch /var/lock/subsys/mysql-proxy
    fi
}

stop() {
    echo -n $"Stopping $prog: "
    killproc -p $PROXY_PID -d 3 $prog
    RETVAL=$?
    echo
    if [ $RETVAL -eq 0 ]; then
        rm -f /var/lock/subsys/mysql-proxy
        rm -f $PROXY_PID
    fi
}
# See how we were called.
case "$1" in
    start)
        start
        ;;
    stop)
        stop
        ;;
    restart)
        stop
        start
        ;;
    condrestart|try-restart)
        if status -p $PROXY_PIDFILE $prog >&/dev/null; then
            stop
            start
        fi
        ;;
    status)
        status -p $PROXY_PID $prog
        ;;
    *)
        echo "Usage: $0 {start|stop|restart|reload|status|condrestart|try-restart}"
        RETVAL=1
        ;;
esac

exit $RETVAL

将上述内容保存为/etc/rc.d/init.d/mysql-proxy，给予执行权限，而后加入到服务列表。
# chmod +x /etc/rc.d/init.d/mysql-proxy
# chkconfig --add mysql-proxy



4.3 为服务脚本提供配置文件/etc/sysconfig/mysql-proxy，内容如下所示：

# Options for mysql-proxy 
ADMIN_USER="admin"
ADMIN_PASSWORD="admin"
ADMIN_ADDRESS=""
ADMIN_LUA_SCRIPT="/usr/local/mysql-proxy/share/doc/mysql-proxy/admin.lua"
PROXY_ADDRESS=""
PROXY_USER="mysql-proxy"
PROXY_OPTIONS="--daemon --log-level=info --log-use-syslog"


其中最后一行，需要按实际场景进行修改，例如：
PROXY_OPTIONS="--daemon --log-level=info --log-use-syslog --plugins=proxy --plugins=admin --proxy-backend-addresses=172.16.100.6:3306 --proxy-read-only-backend-addresses=172.16.100.7:3306 --proxy-lua-script=/usr/local/mysql-proxy/share/doc/mysql-proxy/rw-splitting.lua"

其中的proxy-backend-addresses选项和proxy-read-only-backend-addresses选项均可重复使用多次，以实现指定多个读写服务器或只读服务器。

4.4 mysql-proxy的配置选项

mysql-proxy的配置选项大致可分为帮助选项、管理选项、代理选项及应用程序选项几类，下面一起去介绍它们。

--help
--help-admin
--help-proxy
--help-all ———— 以上四个选项均用于获取帮助信息；

--proxy-address=host:port ———— 代理服务监听的地址和端口；
--admin-address=host:port ———— 管理模块监听的地址和端口；
--proxy-backend-addresses=host:port ———— 后端mysql服务器的地址和端口；
--proxy-read-only-backend-addresses=host:port ———— 后端只读mysql服务器的地址和端口；
--proxy-lua-script=file_name ———— 完成mysql代理功能的Lua脚本；
--daemon ———— 以守护进程模式启动mysql-proxy；
--keepalive ———— 在mysql-proxy崩溃时尝试重启之；
--log-file=/path/to/log_file_name ———— 日志文件名称；
--log-level=level ———— 日志级别；
--log-use-syslog ———— 基于syslog记录日志；
--plugins=plugin,.. ———— 在mysql-proxy启动时加载的插件；
--user=user_name ———— 运行mysql-proxy进程的用户；
--defaults-file=/path/to/conf_file_name ———— 默认使用的配置文件路径；其配置段使用[mysql-proxy]标识；
--proxy-skip-profiling ———— 禁用profile；
--pid-file=/path/to/pid_file_name ———— 进程文件名；




5、复制如下内容建立admin.lua文件，将其保存至/usr/local/mysql-proxy/share/doc/mysql-proxy/目录中。

--[[ $%BEGINLICENSE%$
 Copyright (c) 2007, 2012, Oracle and/or its affiliates. All rights reserved.

 This program is free software; you can redistribute it and/or
 modify it under the terms of the GNU General Public License as
 published by the Free Software Foundation; version 2 of the
 License.

 This program is distributed in the hope that it will be useful,
 but WITHOUT ANY WARRANTY; without even the implied warranty of
 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
 GNU General Public License for more details.

 You should have received a copy of the GNU General Public License
 along with this program; if not, write to the Free Software
 Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA
 02110-1301  USA

 $%ENDLICENSE%$ --]]

function set_error(errmsg) 
	proxy.response = {
		type = proxy.MYSQLD_PACKET_ERR,
		errmsg = errmsg or "error"
	}
end

function read_query(packet)
	if packet:byte() ~= proxy.COM_QUERY then
		set_error("[admin] we only handle text-based queries (COM_QUERY)")
		return proxy.PROXY_SEND_RESULT
	end

	local query = packet:sub(2)

	local rows = { }
	local fields = { }

	if query:lower() == "select * from backends" then
		fields = { 
			{ name = "backend_ndx", 
			  type = proxy.MYSQL_TYPE_LONG },

			{ name = "address",
			  type = proxy.MYSQL_TYPE_STRING },
			{ name = "state",
			  type = proxy.MYSQL_TYPE_STRING },
			{ name = "type",
			  type = proxy.MYSQL_TYPE_STRING },
			{ name = "uuid",
			  type = proxy.MYSQL_TYPE_STRING },
			{ name = "connected_clients", 
			  type = proxy.MYSQL_TYPE_LONG },
		}

		for i = 1, #proxy.global.backends do
			local states = {
				"unknown",
				"up",
				"down"
			}
			local types = {
				"unknown",
				"rw",
				"ro"
			}
			local b = proxy.global.backends[i]

			rows[#rows + 1] = {
				i,
				b.dst.name,          -- configured backend address
				states[b.state + 1], -- the C-id is pushed down starting at 0
				types[b.type + 1],   -- the C-id is pushed down starting at 0
				b.uuid,              -- the MySQL Server's UUID if it is managed
				b.connected_clients  -- currently connected clients
			}
		end
	elseif query:lower() == "select * from help" then
		fields = { 
			{ name = "command", 
			  type = proxy.MYSQL_TYPE_STRING },
			{ name = "description", 
			  type = proxy.MYSQL_TYPE_STRING },
		}
		rows[#rows + 1] = { "SELECT * FROM help", "shows this help" }
		rows[#rows + 1] = { "SELECT * FROM backends", "lists the backends and their state" }
	else
		set_error("use 'SELECT * FROM help' to see the supported commands")
		return proxy.PROXY_SEND_RESULT
	end

	proxy.response = {
		type = proxy.MYSQLD_PACKET_OK,
		resultset = {
			fields = fields,
			rows = rows
		}
	}
	return proxy.PROXY_SEND_RESULT
end


6、测试

6.1 管理功能测试

# mysql -uadmin -padmin -h172.16.100.107 --port=4041 

Welcome to the MySQL monitor.  Commands end with ; or \g.
Your MySQL connection id is 1
Server version: 5.0.99-agent-admin

Type 'help;' or '\h' for help. Type '\c' to clear the buffer.

mysql> SELECT * FROM backends;
+-------------+-------------------+-------+------+------+-------------------+
| backend_ndx | address           | state | type | uuid | connected_clients |
+-------------+-------------------+-------+------+------+-------------------+
|           1 | 172.16.100.6:3306 | up    | rw   | NULL |                 0 | 
|           2 | 172.16.100.7:3306 | up    | ro   | NULL |                 0 | 
+-------------+-------------------+-------+------+------+-------------------+
2 rows in set (0.00 sec)

6.2 读写分离测试

# mysql -uroot -pmagedu.com -h172.16.100.107 --port=4040






















下面的读写分享脚本是由mysql-proxy-0.8.3提供了，将其复制保存为/usr/lib/mysql-proxy/lua/proxy/rw-splitting.lua，就可以启动服务了。

--[[ $%BEGINLICENSE%$
 Copyright (c) 2007, 2012, Oracle and/or its affiliates. All rights reserved.

 This program is free software; you can redistribute it and/or
 modify it under the terms of the GNU General Public License as
 published by the Free Software Foundation; version 2 of the
 License.

 This program is distributed in the hope that it will be useful,
 but WITHOUT ANY WARRANTY; without even the implied warranty of
 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
 GNU General Public License for more details.

 You should have received a copy of the GNU General Public License
 along with this program; if not, write to the Free Software
 Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA
 02110-1301  USA

 $%ENDLICENSE%$ --]]

---
-- a flexible statement based load balancer with connection pooling
--
-- * build a connection pool of min_idle_connections for each backend and maintain
--   its size
-- * 
-- 
-- 

local commands    = require("proxy.commands")
local tokenizer   = require("proxy.tokenizer")
local lb          = require("proxy.balance")
local auto_config = require("proxy.auto-config")

--- config
--
-- connection pool
if not proxy.global.config.rwsplit then
	proxy.global.config.rwsplit = {
		min_idle_connections = 4,
		max_idle_connections = 8,

		is_debug = false
	}
end

---
-- read/write splitting sends all non-transactional SELECTs to the slaves
--
-- is_in_transaction tracks the state of the transactions
local is_in_transaction       = false

-- if this was a SELECT SQL_CALC_FOUND_ROWS ... stay on the same connections
local is_in_select_calc_found_rows = false

--- 
-- get a connection to a backend
--
-- as long as we don't have enough connections in the pool, create new connections
--
function connect_server() 
	local is_debug = proxy.global.config.rwsplit.is_debug
	-- make sure that we connect to each backend at least ones to 
	-- keep the connections to the servers alive
	--
	-- on read_query we can switch the backends again to another backend

	if is_debug then
		print()
		print("[connect_server] " .. proxy.connection.client.src.name)
	end

	local rw_ndx = 0

	-- init all backends 
	for i = 1, #proxy.global.backends do
		local s        = proxy.global.backends[i]
		local pool     = s.pool -- we don't have a username yet, try to find a connections which is idling
		local cur_idle = pool.users[""].cur_idle_connections

		pool.min_idle_connections = proxy.global.config.rwsplit.min_idle_connections
		pool.max_idle_connections = proxy.global.config.rwsplit.max_idle_connections
		
		if is_debug then
			print("  [".. i .."].connected_clients = " .. s.connected_clients)
			print("  [".. i .."].pool.cur_idle     = " .. cur_idle)
			print("  [".. i .."].pool.max_idle     = " .. pool.max_idle_connections)
			print("  [".. i .."].pool.min_idle     = " .. pool.min_idle_connections)
			print("  [".. i .."].type = " .. s.type)
			print("  [".. i .."].state = " .. s.state)
		end

		-- prefer connections to the master 
		if s.type == proxy.BACKEND_TYPE_RW and
		   s.state ~= proxy.BACKEND_STATE_DOWN and
		   cur_idle < pool.min_idle_connections then
			proxy.connection.backend_ndx = i
			break
		elseif s.type == proxy.BACKEND_TYPE_RO and
		       s.state ~= proxy.BACKEND_STATE_DOWN and
		       cur_idle < pool.min_idle_connections then
			proxy.connection.backend_ndx = i
			break
		elseif s.type == proxy.BACKEND_TYPE_RW and
		       s.state ~= proxy.BACKEND_STATE_DOWN and
		       rw_ndx == 0 then
			rw_ndx = i
		end
	end

	if proxy.connection.backend_ndx == 0 then
		if is_debug then
			print("  [" .. rw_ndx .. "] taking master as default")
		end
		proxy.connection.backend_ndx = rw_ndx
	end

	-- pick a random backend
	--
	-- we someone have to skip DOWN backends

	-- ok, did we got a backend ?

	if proxy.connection.server then 
		if is_debug then
			print("  using pooled connection from: " .. proxy.connection.backend_ndx)
		end

		-- stay with it
		return proxy.PROXY_IGNORE_RESULT
	end

	if is_debug then
		print("  [" .. proxy.connection.backend_ndx .. "] idle-conns below min-idle")
	end

	-- open a new connection 
end

--- 
-- put the successfully authed connection into the connection pool
--
-- @param auth the context information for the auth
--
-- auth.packet is the packet
function read_auth_result( auth )
	if is_debug then
		print("[read_auth_result] " .. proxy.connection.client.src.name)
	end
	if auth.packet:byte() == proxy.MYSQLD_PACKET_OK then
		-- auth was fine, disconnect from the server
		proxy.connection.backend_ndx = 0
	elseif auth.packet:byte() == proxy.MYSQLD_PACKET_EOF then
		-- we received either a 
		-- 
		-- * MYSQLD_PACKET_ERR and the auth failed or
		-- * MYSQLD_PACKET_EOF which means a OLD PASSWORD (4.0) was sent
		print("(read_auth_result) ... not ok yet");
	elseif auth.packet:byte() == proxy.MYSQLD_PACKET_ERR then
		-- auth failed
	end
end


--- 
-- read/write splitting
function read_query( packet )
	local is_debug = proxy.global.config.rwsplit.is_debug
	local cmd      = commands.parse(packet)
	local c        = proxy.connection.client

	local r = auto_config.handle(cmd)
	if r then return r end

	local tokens
	local norm_query

	-- looks like we have to forward this statement to a backend
	if is_debug then
		print("[read_query] " .. proxy.connection.client.src.name)
		print("  current backend   = " .. proxy.connection.backend_ndx)
		print("  client default db = " .. c.default_db)
		print("  client username   = " .. c.username)
		if cmd.type == proxy.COM_QUERY then 
			print("  query             = "        .. cmd.query)
		end
	end

	if cmd.type == proxy.COM_QUIT then
		-- don't send COM_QUIT to the backend. We manage the connection
		-- in all aspects.
		proxy.response = {
			type = proxy.MYSQLD_PACKET_OK,
		}
	
		if is_debug then
			print("  (QUIT) current backend   = " .. proxy.connection.backend_ndx)
		end

		return proxy.PROXY_SEND_RESULT
	end
	
	-- COM_BINLOG_DUMP packet can't be balanced
	--
	-- so we must send it always to the master
	if cmd.type == proxy.COM_BINLOG_DUMP then
		-- if we don't have a backend selected, let's pick the master
		--
		if proxy.connection.backend_ndx == 0 then
			proxy.connection.backend_ndx = lb.idle_failsafe_rw()
		end

		return
	end

	proxy.queries:append(1, packet, { resultset_is_needed = true })

	-- read/write splitting 
	--
	-- send all non-transactional SELECTs to a slave
	if not is_in_transaction and
	   cmd.type == proxy.COM_QUERY then
		tokens     = tokens or assert(tokenizer.tokenize(cmd.query))

		local stmt = tokenizer.first_stmt_token(tokens)

		if stmt.token_name == "TK_SQL_SELECT" then
			is_in_select_calc_found_rows = false
			local is_insert_id = false

			for i = 1, #tokens do
				local token = tokens[i]
				-- SQL_CALC_FOUND_ROWS + FOUND_ROWS() have to be executed 
				-- on the same connection
				-- print("token: " .. token.token_name)
				-- print("  val: " .. token.text)
				
				if not is_in_select_calc_found_rows and token.token_name == "TK_SQL_SQL_CALC_FOUND_ROWS" then
					is_in_select_calc_found_rows = true
				elseif not is_insert_id and token.token_name == "TK_LITERAL" then
					local utext = token.text:upper()

					if utext == "LAST_INSERT_ID" or
					   utext == "@@INSERT_ID" then
						is_insert_id = true
					end
				end

				-- we found the two special token, we can't find more
				if is_insert_id and is_in_select_calc_found_rows then
					break
				end
			end

			-- if we ask for the last-insert-id we have to ask it on the original 
			-- connection
			if not is_insert_id then
				local backend_ndx = lb.idle_ro()

				if backend_ndx > 0 then
					proxy.connection.backend_ndx = backend_ndx
				end
			else
				print("   found a SELECT LAST_INSERT_ID(), staying on the same backend")
			end
		end
	end

	-- no backend selected yet, pick a master
	if proxy.connection.backend_ndx == 0 then
		-- we don't have a backend right now
		-- 
		-- let's pick a master as a good default
		--
		proxy.connection.backend_ndx = lb.idle_failsafe_rw()
	end

	-- by now we should have a backend
	--
	-- in case the master is down, we have to close the client connections
	-- otherwise we can go on
	if proxy.connection.backend_ndx == 0 then
		return proxy.PROXY_SEND_QUERY
	end

	local s = proxy.connection.server

	-- if client and server db don't match, adjust the server-side 
	--
	-- skip it if we send a INIT_DB anyway
	if cmd.type ~= proxy.COM_INIT_DB and 
	   c.default_db and c.default_db ~= s.default_db then
		print("    server default db: " .. s.default_db)
		print("    client default db: " .. c.default_db)
		print("    syncronizing")
		proxy.queries:prepend(2, string.char(proxy.COM_INIT_DB) .. c.default_db, { resultset_is_needed = true })
	end

	-- send to master
	if is_debug then
		if proxy.connection.backend_ndx > 0 then
			local b = proxy.global.backends[proxy.connection.backend_ndx]
			print("  sending to backend : " .. b.dst.name);
			print("    is_slave         : " .. tostring(b.type == proxy.BACKEND_TYPE_RO));
			print("    server default db: " .. s.default_db)
			print("    server username  : " .. s.username)
		end
		print("    in_trans        : " .. tostring(is_in_transaction))
		print("    in_calc_found   : " .. tostring(is_in_select_calc_found_rows))
		print("    COM_QUERY       : " .. tostring(cmd.type == proxy.COM_QUERY))
	end

	return proxy.PROXY_SEND_QUERY
end

---
-- as long as we are in a transaction keep the connection
-- otherwise release it so another client can use it
function read_query_result( inj ) 
	local is_debug = proxy.global.config.rwsplit.is_debug
	local res      = assert(inj.resultset)
  	local flags    = res.flags

	if inj.id ~= 1 then
		-- ignore the result of the USE <default_db>
		-- the DB might not exist on the backend, what do do ?
		--
		if inj.id == 2 then
			-- the injected INIT_DB failed as the slave doesn't have this DB
			-- or doesn't have permissions to read from it
			if res.query_status == proxy.MYSQLD_PACKET_ERR then
				proxy.queries:reset()

				proxy.response = {
					type = proxy.MYSQLD_PACKET_ERR,
					errmsg = "can't change DB ".. proxy.connection.client.default_db ..
						" to on slave " .. proxy.global.backends[proxy.connection.backend_ndx].dst.name
				}

				return proxy.PROXY_SEND_RESULT
			end
		end
		return proxy.PROXY_IGNORE_RESULT
	end

	is_in_transaction = flags.in_trans
	local have_last_insert_id = (res.insert_id and (res.insert_id > 0))

	if not is_in_transaction and 
	   not is_in_select_calc_found_rows and
	   not have_last_insert_id then
		-- release the backend
		proxy.connection.backend_ndx = 0
	elseif is_debug then
		print("(read_query_result) staying on the same backend")
		print("    in_trans        : " .. tostring(is_in_transaction))
		print("    in_calc_found   : " .. tostring(is_in_select_calc_found_rows))
		print("    have_insert_id  : " .. tostring(have_last_insert_id))
	end
end

--- 
-- close the connections if we have enough connections in the pool
--
-- @return nil - close connection 
--         IGNORE_RESULT - store connection in the pool
function disconnect_client()
	local is_debug = proxy.global.config.rwsplit.is_debug
	if is_debug then
		print("[disconnect_client] " .. proxy.connection.client.src.name)
	end

	-- make sure we are disconnection from the connection
	-- to move the connection into the pool
	proxy.connection.backend_ndx = 0
end