目前較爲常見的mysql讀寫分離分爲兩種：
一、
基於程序代碼內部實現：在代碼中對select操做分發到從庫；其它操做由主庫執行；這類方法也是目前生產環境應用最普遍，知名的如DISCUZ
X2。優勢是性能較好，由於在程序代碼中實現，不須要增長額外的設備做爲硬件開支。缺點是須要開發人員來實現，運維人員無從下手。 java
二、 基於中間代理層實現：咱們都知道代理通常是位於客戶端和服務器之間，代理服務器接到客戶端請求後經過判斷而後轉發到後端數據庫。在這有兩個表明性程序 mysql
mysql-proxy：mysql-proxy爲mysql開源項目，經過其自帶的lua腳本進行sql判斷，雖然是mysql官方產品，可是mysql官方並不建議將mysql-proxy用到生產環境。
amoeba：由陳思儒開發，做者曾就任於阿里巴巴，現就任於盛大。該程序由java語言進行開發，目前只據說阿里巴巴將其用於生產環境。另外，此項目嚴重缺乏維護和推廣（做者有個官方博客，不少用戶反饋的問題發現做者不理睬）
通過上述簡單的比較，經過程序代碼實現mysql讀寫分離天然是一個不錯的選擇。可是並非全部的應用都適合在程序代碼中實現讀寫分離，像大型SNS、B2C這類應用能夠在代碼中實現，由於這樣對程序代碼自己改動較小；像一些大型複雜的java應用，這種類型的應用在代碼中實現對代碼改動就較大了。因此，像這種應用通常就會考慮使用代理層來實現。 sql
下面咱們看一下如何搭建mysql-proxy來實現mysql讀寫分離
環境拓撲以下：
關於mysql、mysql主從的搭建，在此再也不演示，以下的操做均在mysql-proxy（192.168.1.200）服務器進行
1、安裝mysql-proxy
一、安裝lua (mysql-proxy須要使用lua腳本進行數據轉發)
#tar zxvf
lua-5.1.4.tar.gz
#cd lua-5.1.4
#vi Makefile，修改INSTALL_TOP=
/usr/local/lua
#make posix
#make install
二、安裝libevent
#tar
zxvf libevent-2.0.8-rc.tar.gz
#cd libevent-2.0.8-rc
#./configure
--prefix=/usr/local/libevent
#make && make install
三、安裝check
#tar zxvf check-0.9.8.tar.gz
#cd check-0.9.8
#./configure && make && make install
四、安裝mysql客戶端
#tar zxvf mysql-5.0.92.tar.gz
#cd mysql-5.0.92
#./configure
--without-server && make && make install
五、設置環境變量
（安裝mysql-proxy所需變量）
#vi /etc/profile
export
LUA_CFLAGS="-I/usr/local/lua/include" LUA_LIBS="-L/usr/local/lua/lib -llua -ldl"
LDFLAGS="-L/usr/local/libevent/lib -lm"
export
CPPFLAGS="-I/usr/local/libevent/include"
export
CFLAGS="-I/usr/local/libevent/include"
# source /etc/profile
六、安裝mysql-proxy
#tar zxvf mysql-proxy-0.6.0.tar.gz
#cd
mysql-proxy-0.6.0
# ./configure --prefix=/usr/local/mysql-proxy --with-mysql
--with-lua
#make && make install
七、啓動mysql-proxy
本次對兩臺數據庫實現了讀寫分離；mysql-master爲可讀可寫，mysql-slave爲只讀
#/usr/local/mysql-proxy/sbin/mysql-proxy
--proxy-backend-addresses=192.168.1.201:3306
--proxy-read-only-backend-addresses=192.168.1.202:3306
--proxy-lua-script=/usr/local/mysql-proxy/share/mysql-proxy/rw-splitting.lua
&
注：若是正常狀況下啓動後終端不會有任何提示信息，mysql-proxy啓動後會啓動兩個端口4040和4041，4040用於SQL轉發，4041用於管理mysql-proxy。若有多個mysql-slave能夠依次在後面添加
2、測試
一、鏈接測試
由於默認狀況下mysql數據庫不容許用戶在遠程鏈接
mysql>grant
all privileges on *.* to identified by '123456';
mysql>flush privileges;
客戶端鏈接
#mysql -uroot -p123456 -h192.168.1.200 -P4040
二、讀寫分離測試
爲了測試出mysql讀寫分離的真實性，在測試以前，須要開啓兩臺mysql的log功能，而後在mysql-slave服務器中止複製
① 在兩臺mysql配置文件my.cnf中加入log=query.log，而後重啓 數據庫
②在mysql-slave上執行SQL語句stop slave 後端
③在兩臺mysql上執行#tail -f /usr/local/mysql/var/query.log 服務器
④在客戶端上鍊接mysql（三個鏈接以上），而後執行create、select等SQL語句，觀察兩臺mysql的日誌有何變化
注：生產環境中除了進行程序調試外，其它不要開啓mysql查詢日誌，由於查詢日誌記錄了客戶端的全部語句，頻繁的IO操做將會致使mysql總體性能降低
總結：在上述環境中，mysql-proxy和mysql-master、mysql-slave三臺服務器均存在單點故障。若是在可用性要求較高的場合，單點隱患是絕對不容許的。爲了不mysql-proxy單點隱患有兩種方法，一種方法是mysql-proxy配合keepalived作雙機，另外一種方法是將mysql-proxy和應用服務安裝到同一臺服務器上；爲了不mysql-master單點故障可使用DRBD+heartbear作雙機；避免mysql-slave單點故障增長多臺mysql-slave便可，由於mysql-proxy會自動屏蔽後端發生故障的mysql-slave。 app
附: mysql-proxy LUA 讀寫分離腳本代碼: 運維
--[[
--
-- author : KDr2
-- version 0.01
-- SYNOPSIS:
---
1.維護了一個鏈接池
--- 2.讀寫分離，簡單的將select開頭的語句放到slave上執行
---
3.事務支持，全部事務放到master上執行，事務中不更改鏈接
--- 4.簡單日誌
--
--]] ide
--- config vars
local min_idle_connections = 4
local
max_idle_connections = 8
local log_level=1
local encoding="utf8"
---
end of config 性能
-- 事務標識，在事務內不歸還鏈接
local
transaction_flags={}
setmetatable(transaction_flags,{__index=function()
return 0 end})
-- log system
log={
level={debug=1,info=2,warn=3,error=4},
funcs={"debug","info","warn","error"},
}
function log.log(level,m)
if level >= log_level then
local msg="[" .. os.date("%Y-%m-%d %X")
.."] ".. log.funcs[level] .. ": " .. tostring(m)
print(msg) -- TODO
write msg into a log file.
end
end
for i,v in ipairs(log.funcs)
do
log[v]=function(m) log.log(log.level[v],m) end
end
-- connect to server
function connect_server()
log.info(" starting
connect_server ... ")
local least_idle_conns_ndx = 0
local
least_idle_conns = 0
for i = 1, #proxy.backends do
local s
= proxy.backends[i]
local pool = s.pool
local cur_idle =
pool.users[""].cur_idle_connections
log.debug("[".. s.address .."].connected_clients = " ..
s.connected_clients)
log.debug("[".. s.address .."].idling_connections
= " .. cur_idle)
log.debug("[".. s.address .."].type = " ..
s.type)
log.debug("[".. s.address .."].state = " .. s.state)
if s.state ~= proxy.BACKEND_STATE_DOWN then
-- try to
connect to each backend once at least
if cur_idle == 0
then
proxy.connection.backend_ndx = i
log.info("server [".. proxy.backends[i].address .."] open new
connection")
return
end
-- try to open at
least min_idle_connections
if least_idle_conns_ndx == 0
or
( cur_idle < min_idle_connections and
cur_idle < least_idle_conns ) then
least_idle_conns_ndx =
i
least_idle_conns = cur_idle
end
end
end
if least_idle_conns_ndx > 0 then
proxy.connection.backend_ndx
= least_idle_conns_ndx
end
if proxy.connection.backend_ndx
> 0 then
local s =
proxy.backends[proxy.connection.backend_ndx]
local pool = s.pool
local cur_idle = pool.users[""].cur_idle_connections
if cur_idle >= min_idle_connections then
-- we have 4
idling connections in the pool, that's good enough
log.debug("using
pooled connection from: " .. proxy.connection.backend_ndx)
return
proxy.PROXY_IGNORE_RESULT
end
end
-- open a new connection
log.info("opening new connection on: " ..
proxy.backends[proxy.connection.backend_ndx].address)
end
---
-- auth.packet is the packet
function read_auth_result( auth )
if
auth.packet:byte() == proxy.MYSQLD_PACKET_OK then
-- 鏈接正常
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
log.error("(read_auth_result) ...
not ok yet");
elseif auth.packet:byte() == proxy.MYSQLD_PACKET_ERR
then
log.error("auth failed!")
end
end
---
-- read/write splitting
function read_query( packet )
log.debug("[read_query]")
log.debug("authed backend = " ..
proxy.connection.backend_ndx)
log.debug("used db = " ..
proxy.connection.client.default_db)
if packet:byte() == proxy.COM_QUIT then
proxy.response =
{
type = proxy.MYSQLD_PACKET_OK,
}
return
proxy.PROXY_SEND_RESULT
end
if proxy.connection.backend_ndx == 0 then
local
is_read=(string.upper(packet:sub(2))):match("^SELECT")
local
target_type=proxy.BACKEND_TYPE_RW
if is_read then
target_type=proxy.BACKEND_TYPE_RO end
for i = 1, #proxy.backends
do
local s = proxy.backends[i]
local pool = s.pool
local cur_idle =
pool.users[proxy.connection.client.username].cur_idle_connections
if cur_idle > 0 and
s.state ~=
proxy.BACKEND_STATE_DOWN and
s.type == target_type
then
proxy.connection.backend_ndx = i
break
end
end
end
-- sync the client-side
default_db with the server-side default_db
if proxy.connection.server and
proxy.connection.client.default_db ~= proxy.connection.server.default_db
then
local server_db=proxy.connection.server.default_db
local
client_db=proxy.connection.client.default_db
local default_db=
(#client_db > 0) and client_db or server_db
if #default_db > 0
then
proxy.queries:append(2, string.char(proxy.COM_INIT_DB) ..
default_db)
proxy.queries:append(2, string.char(proxy.COM_QUERY) ..
"set names '" .. encoding .."'")
log.info("change database to " ..
default_db);
end
end
if proxy.connection.backend_ndx > 0
then
log.debug("Query[" .. packet:sub(2) .. "] Target is [" ..
proxy.backends[proxy.connection.backend_ndx].address .."]")
end
proxy.queries:append(1, packet)
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 res = assert(inj.resultset)
local flags =
res.flags
if inj.id ~= 1 then
-- ignore the result of the USE
<default_db>
return proxy.PROXY_IGNORE_RESULT
end
is_in_transaction = flags.in_trans
if flags.in_trans then
transaction_flags[proxy.connection.server.thread_id] =
transaction_flags[proxy.connection.server.thread_id] + 1
elseif
inj.query:sub(2):lower():match("^%s*commit%s*$") or
inj.query:sub(2):lower():match("^%s*rollback%s*$") then
transaction_flags[proxy.connection.server.thread_id] =
transaction_flags[proxy.connection.server.thread_id] - 1
if
transaction_flags[proxy.connection.server.thread_id] < 0 then
transaction_flags[proxy.connection.server.thread_id] = 0 end
end
log.debug("transaction res : " ..
tostring(transaction_flags[proxy.connection.server.thread_id]));
if
transaction_flags[proxy.connection.server.thread_id]==0 or
transaction_flags[proxy.connection.server.thread_id] == nil then
--
isnot in a transaction, need to release the backend
proxy.connection.backend_ndx = 0
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()
log.debug("[disconnect_client]")
if proxy.connection.backend_ndx == 0
then
for i = 1, #proxy.backends do
local s =
proxy.backends[i]
local pool = s.pool
local cur_idle =
pool.users[proxy.connection.client.username].cur_idle_connections
if s.state ~= proxy.BACKEND_STATE_DOWN and
cur_idle
> max_idle_connections then
-- try to disconnect a
backend
proxy.connection.backend_ndx = i
log.info("[".. proxy.backends[i].address .."] closing connection, idling: " ..
cur_idle)
return
end
end
return
proxy.PROXY_IGNORE_RESULT
end
end