Oracle 12c引入了一些大量的新特性,資料庫隱藏引數12.2比11.2就多了2000多個, 同時對之前版本的結構也發生了一些變化,雖然不如有些特性像temporary undo\immemory\多租戶那麼受人重視.如DB_WRITER_PROCESSES DBWR最大程式數從10GR2的20到11gr2的36再到12C R2的100,Archiver Process程式數也從10增加到了30, 還有本篇要講的Listenr的註冊程式的改變. 在12c以前的版本中服務註冊一直都是PMON程式負責, 從12c起引入了LREG (listener registration)後臺程式接管了這部分工作減輕PMON的工作,同樣如果LREG 程式死了例項也會crash.

As with PMON in pre-12c versions, LREG (during registration) process provides the listener with information about the following:
* Names of the database services provided by the database
* Name of the database instance associated with the services and its current and maximum load
* Service handlers (dispatchers and dedicated servers) available for the instance, including their type, protocol addresses, and current and maximum load (for LBA)

listener沒有啟動LREG程式不能註冊服務,LREG但是會每60秒嘗試註冊,如果local_listener沒有配置,LREG會嘗試連線預設的1521埠,直到監聽程式啟動, 如果Listener啟動後LREG週期註冊前,同樣也可以使用”alter system register”立即註冊服務.litener的註冊資訊可以使用listener_registration event dump在lreg trace中.

測試版本 oracle 12.2 EE on OEL6

alter system set events = 'immediate trace name listener_registration level 3';

檢視lreg trace檔案.
— 未啟動listener時 —

*** 2017-02-22T15:58:04.665213+08:00 (CDB$ROOT(1))
kmlwait: status: succ=0, wait=0, fail=1
kmmlrl: listener failure retry: 6002
kmmlrl: 48 processes
kmmlrl: instance load 1
kmmlrl_network_hdlr_state: update
kmmlrl_network_hdlr_state: update for network '-oracledefault-'
kmmlrl_network_hdlr_state: beq handler: load=48, max=299, flag=0x80002002, upd=0x2
kmmlrl: nsgr update returned 0
kmmlrl: nsgr register returned 0
kmlwait: LREG woken up to process network events after 0 cs
kmlwait: status: succ=0, wait=0, fail=1
*** 2017-02-22T15:58:07.666581+08:00 (CDB$ROOT(1))
kmlwait: status: succ=0, wait=0, fail=1
...
kmlwait: status: succ=0, wait=0, fail=1
*** 2017-02-22T15:58:58.683514+08:00 (CDB$ROOT(1))
kmlwait: status: succ=0, wait=0, fail=1
*** 2017-02-22T15:59:01.683720+08:00 (CDB$ROOT(1))
kmlwait: status: succ=0, wait=0, fail=1
*** 2017-02-22T15:59:04.684796+08:00 (CDB$ROOT(1))
kmlwait: status: succ=0, wait=0, fail=1
kmmlrl: listener failure retry: 6001
kmmlrl: 48 processes
kmmlrl: instance load 1
kmmlrl_network_hdlr_state: update
kmmlrl_network_hdlr_state: update for network '-oracledefault-'
kmmlrl_network_hdlr_state: beq handler: load=48, max=299, flag=0x80002002, upd=0x2
kmmlrl: nsgr update returned 0
kmmlrl: nsgr register returned 0
kmlwait: LREG woken up to process network events after 0 cs
kmlwait: status: succ=0, wait=0, fail=1

# 啟動了LISTENRE後

*** 2017-02-22T16:00:04.699377+08:00 (CDB$ROOT(1))
kmlwait: status: succ=0, wait=0, fail=1
kmmlrl: listener failure retry: 6002
kmmlrl: 46 processes
kmmlrl: instance load 0
kmmlrl_network_hdlr_state: update
kmmlrl_network_hdlr_state: update for network '-oracledefault-'
kmmlrl_network_hdlr_state: beq handler: load=46, max=299, flag=0x80002002, upd=0x2
kmmlrl: nsgr update returned 0
kmmlrl: nsgr register returned 0
kmlwait: LREG woken up to process network events after 8 cs
kmlwait: status: succ=0, wait=1, fail=0
kmlwait: LREG woken up to process network events after 11 cs
kmlwait: status: succ=0, wait=1, fail=0
kmlwait: LREG woken up to process network events after 11 cs
kmlwait: status: succ=0, wait=1, fail=0
kmlwait: LREG woken up to process network events after 18 cs
kmlwait: status: succ=1, wait=0, fail=0
*** 2017-02-22T16:00:07.701048+08:00 (CDB$ROOT(1))
kmlwait: status: succ=1, wait=0, fail=0
*** 2017-02-22T16:00:10.703823+08:00 (CDB$ROOT(1))
kmlwait: status: succ=1, wait=0, fail=0
*** 2017-02-22T16:00:13.704938+08:00 (CDB$ROOT(1))
kmlwait: status: succ=1, wait=0, fail=0
...
*** 2017-02-22T16:01:10.723033+08:00 (CDB$ROOT(1))
kmlwait: status: succ=1, wait=0, fail=0
*** 2017-02-22T16:01:13.724132+08:00 (CDB$ROOT(1))
kmlwait: status: succ=1, wait=0, fail=0
*** 2017-02-22T16:01:16.725179+08:00 (CDB$ROOT(1))
kmlwait: status: succ=1, wait=0, fail=0
kmmlrl_disp_check: update for time delta: 60025
kmmlrl: 49 processes
kmmlrl: node load 10
kmmlrl_network_hdlr_state: update for network '-oracledefault-'
kmmlrl_network_hdlr_state: beq handler: load=49, max=299, flag=0x80002002, upd=0x2
kmmlrl_disp_update_hdlr: D000 load 0
kmmlrl: nsgr update returned 0
kmlwait: LREG woken up to process network events after 0 cs
kmlwait: status: succ=1, wait=0, fail=0
*** 2017-02-22T16:01:19.727075+08:00 (CDB$ROOT(1))
kmlwait: status: succ=1, wait=0, fail=0
*** 2017-02-22T16:01:22.727602+08:00 (CDB$ROOT(1))
kmlwait: status: succ=1, wait=0, fail=0
Last update: 318704 (14 seconds ago)
Flag: 0x4, 0x0
State: succ=1, wait=0, fail=0
CDB: root pdb 1 last pdb 4098 open max pdb 2
Dispatcher configuration index: cur 1 max 1
Network '-oracledefault-' pdb 1 :
  Local listeners:
  0 - (ADDRESS=(PROTOCOL=TCP)(HOST=anbob.com)(PORT=1521)) pdb 1 dci 0
       state=1, err=0
       nse[0]=0, nse[1]=0, nte[0]=0, nte[1]=0, nte[2]=0
       ncre=0
       endp=(DESCRIPTION=(ADDRESS=(PROTOCOL=tcp)(HOST=anbob.com)(PORT=1521)))
         flg=0x80000000 nse=0 pri=0x7f4d5ed876f0
         hdlr flg=0x4 hdlr map count=0 eflg=0x4 pri=0x7f4d5ed88d98
  Remote listeners:
  Handlers:
    Dedicated
       flg=0x80002002, upd=0x2, srvl=3
       services=anbob.com,
                pdbanbob.com,
                465fa0ab8243396ae0530338a8c0fc9e.com
       hdlr load=49, max=299
       nam=DEDICATED
       inf=LOCAL SERVER
       pri=0x7f4d5ed87208
    Local listener 0 pdb 1
       flg=0x2, upd=0x8, srvl=3
       services=anbob.com,
                pdbanbob.com,
                465fa0ab8243396ae0530338a8c0fc9e.com
       hdlr load=0, max=0
       nam=DEDICATED
       adr=(ADDRESS=(PROTOCOL=TCP)(HOST=anbob.com)(PORT=1521))
       inf=REMOTE SERVER
       pri=0x7f4d5ed87808
    chidx=3 flg=0x1 ccflag=0x0
    chidx=2 flg=0x1 ccflag=0x0
    chidx=1 flg=0x1 ccflag=0x0
    chidx=0 flg=0x1 ccflag=0x0
Listeners:
Instance: anbob (PDB 1 flag 0x1 state 1)
  flg=0x0, upd=0xa
  info=(INF=(HOST=anbob)(REGION=)(DB_NAME=anbob)(VINST_NAME=))
  node load=10, max=5120
  inst load=1, max=472
  pri=0x7f4d5ed87028
Instance: anbob (PDB 2 flag 0x1 state 1)
  flg=0x0, upd=0xa
  info=(INF=(HOST=anbob)(REGION=)(DB_NAME=anbob)(VINST_NAME=))
  node load=10, max=5120
  inst load=1, max=472
  pri=0x7f4d5ed889f0
  0 - anbob.com
       flg=0x104, upd=0x2, pdb=1
       goodnes=0, delta=1, pri=0x7f4d5ed871a8
  1 - pdbanbob.com
       flg=0x104, upd=0x0, pdb=3
       goodnes=0, delta=0, pri=0x7f4d5ed88ab0
  2 - 465fa0ab8243396ae0530338a8c0fc9e.com
       flg=0x104, upd=0x0, pdb=3
       goodnes=0, delta=0, pri=0x7f4d5ed88a50
  3 - anbobXDB.com
       flg=0x105, upd=0x2, pdb=1
       goodnes=0, delta=1, pri=0x7f4d5ed87148
 Inactive Services:
 Deleted Services:
Service ACLs:
Dump ACLs:
Handlers:
  0 - Dedicated
       flg=0x2002, upd=0x2, srvl=4
       services=anbob.com,
                pdbanbob.com,
                465fa0ab8243396ae0530338a8c0fc9e.com
       hdlr load=49, max=299
       nam=DEDICATED
       adr=(ADDRESS=(PROTOCOL=BEQ)(PROGRAM=/u02/app/oracle/product/12.2.0/db_1/bin/oracle)(ARGV0='oracleanbob')(ARGS='(LOCAL=NO)'))
       inf=LOCAL SERVER
       pri=0x7f4d5ed870e8
Dispatcher Handlers:
  0 - D000(1)
       addr=(ADDRESS=(PROTOCOL=tcp)(HOST=anbob.com)(PORT=24297))
       inf=DISPATCHER 
       flg=0x1004, upd=0x2, srvl=1
       services=anbobXDB.com
       hdlr load=0, max=1022
       nam=D000
       adr=(ADDRESS=(PROTOCOL=tcp)(HOST=anbob.com)(PORT=24297))
       inf=DISPATCHER 
       pri=0x7f4d5ed87b58
CMON Handlers for Listener Networks:
Listen Endpoints:
       flg=0x80000000, nse=0
       lad=, lflg=0x73
       pre=HTTPS, sta=12541 mrg=(ADDRESS=(PROTOCOL=TCP)(HOST=anbob.com)(PORT=1521)) pri=0x7f4d5ed88c80
CONH Stats Current:
       chidx=0, num_conn=0, max_num_conn=0
       num_disc=0, num_acc=0, num_handlers=0
       chidx=1, num_conn=0, max_num_conn=0
       num_disc=0, num_acc=0, num_handlers=0
       chidx=2, num_conn=0, max_num_conn=0
       num_disc=0, num_acc=0, num_handlers=0
       chidx=3, num_conn=0, max_num_conn=0
       num_disc=0, num_acc=0, num_handlers=0
CONH Stats Global:
       chidx=0, num_conn=0, max_num_conn=0
       num_disc=0, num_acc=0, num_handlers=0
       chidx=1, num_conn=0, max_num_conn=0
       num_disc=0, num_acc=0, num_handlers=0
       chidx=2, num_conn=0, max_num_conn=0
       num_disc=0, num_acc=0, num_handlers=0
       chidx=3, num_conn=0, max_num_conn=0
       num_disc=0, num_acc=0, num_handlers=0
Per PDB State:
  pdb 1 state 1 sserv 1 rootparam 0 rootmap 0
  pdb 2 state 1 sserv 1 rootparam 1 rootmap 1
  pdb 3 state 0 sserv 1 rootparam 1 rootmap 1
----------------------------
End Registration Information
----------------------------
*** 2017-02-22T16:01:33.929347+08:00 (CDB$ROOT(1))

# 檢視1521埠的程式資訊

[oracle@anbob trace]$ lsof -iTCP:1521
COMMAND    PID   USER   FD   TYPE DEVICE SIZE/OFF NODE NAME
ora_lreg_ 4008 oracle   12u  IPv4  18960      0t0  TCP anbob.com:45857->anbob.com:ncube-lm (ESTABLISHED)
tnslsnr   5255 oracle    8u  IPv6  18775      0t0  TCP *:ncube-lm (LISTEN)
tnslsnr   5255 oracle   14u  IPv6  18961      0t0  TCP anbob.com:ncube-lm->anbob.com:45857 (ESTABLISHED)

Which statement is true about Oracle Net Listener?

A.  It acts as the listening endpoint for the Oracle database instance for all local and nonlocal user connections.

B.  A single listener can service only one database instance and multiple remote client connections.

C.  Service registration with the listener is performed by the process monitor (LREG) process of each database instance.

D.  The listener.ora configuration file must be configured with one or more listening protocol addresses to allow remote users to connect to a database instance.

E.  The listener.ora configuration file must be located in the ORACLE_HOME/network/admin directly.

 

【題意簡述】

考察了Oracle 12c新特性——LREG程式負責監聽器的註冊(Listener Registration)。

 

【考點分析】

Oracle監聽器 Net Listener 是一個重要的資料庫伺服器元件，在整個 Oracle 體系結構中，扮演著重要的作用。它負責管理Oracle 資料庫和客戶端之間的通訊，它在一個特定的網路卡埠 （預設是TCP 1521埠）上監聽連線請求，並將連線轉發給資料庫。

Oracle監聽器主要負責下面的幾方面功能：

l  監聽客戶端請求。

l  為客戶端請求分配 Server Process

l  註冊例項服務

l  錯誤轉移 failover

l  負載均衡

    其中，failover和負載均衡都是RAC架構下的功能。

 

本質上講，Listener是建立例項和客戶端程式之間聯絡的橋樑。 Listener 與例項之間的聯絡，就是透過註冊的過程來實現的。註冊的過程就是例項告訴監聽器，它的資料庫例項名稱instance_name和服務名 service_names。監聽器註冊上這樣的資訊，對客戶端請求根據監聽的註冊資訊，找到正確的服務例項名稱。目前 Oracle提供動態註冊和靜態註冊兩種方式。

靜態註冊就是例項啟動時讀取 listener.ora 檔案的配置，將例項和服務註冊到監聽程式。無論何時啟動一個資料庫，預設地都有兩條資訊註冊到監聽器中：資料庫伺服器對應的例項和服務。

動態註冊的動作是監聽器所在主機上資料庫例項完成。例項的後臺程式每隔一段時間就會將例項的參 數資訊註冊到監聽器上，實現動態註冊。

大家都知道，在Oracle Database 11g以及之前版本，PMON程式負責註冊例項服務。而在Oracle Database 12c中，大量新的後臺程式被引入進來，其中就包括專門負責註冊例項服務的LREG後臺程式。

 

我們節選官方文件中關於PMON 和LREG 的定義，其中專門提到了12c 和之前版本的區別：

“

……

Process Monitor Process (PMON)

The process monitor (PMON) monitors the other background processes and performs process recovery when a server or dispatcher process terminates abnormally.

PMON is responsible for cleaning up the database buffer cache and freeing resources that the client process was using. For example, PMON resets the status of the active  , releases locks that are no longer required, and removes the process ID from the list of active processes.

Listener Registration Process (LREG)

The   registers information about the database instance and dispatcher processes with the Oracle Net Listener. When an instance starts, LREG polls the listener to determine whether it is running. If the listener is running, then LREG passes it relevant parameters. If it is not running, then LREG periodically attempts to contact it.

Note:

In releases before Oracle Database 12c, PMON performed the listener registration.

…… ”

 

【答案剖析】

A， 監聽器負責監聽非本地使用者的連線請求。例如我們熟知的sqlplus / as sysdba 命令是作業系統使用者驗證登入方式，透過OS本地的IPC可以直接連線到例項，而IPC由本地OS提供，允許各種程式在主機內進行通訊，所以不需要listener也可以連線到例項。所以A錯誤。

B，  監聽器執行在資料庫伺服器之上，可以與一個 或多個 Oracle 例項相關聯，所以 B 錯誤 。

C，  本質上講，Listener  是建立例項和客戶端程式之間聯絡的橋樑。 Listener  與例項之間的聯絡，就是透過註冊的過程來實現的。從12c 版本開始，LREG 後臺程式負責註冊例項服務。所以C正確。

D， 在配置listener.ora時會遇到Host引數，該引數作用就是指定連線的主機地址。我們可以選擇IP地址和主機伺服器名稱。兩種方法下，Oracle監聽器是採用不同的策略方法。當使用HOST主機名的時候，Oracle監聽器會對該計算機上所有的IP地址開啟監聽動作；如果使用IP地址，監聽程式只能監聽對應的IP地址。所以D錯誤。

E，  預設情況下，listener.ora 配置檔案存放在ORACLE_HOME/network/admin目錄下，但是我們可以修改配置檔案的存放路徑。以Windows環境為例，我們可以透過定義TNS_ADMIN環境變數來指定listener.ora、tnsnames.ora等配置檔案的預設存放路徑。所以E錯誤。

 

【答案】C

在Oracle Database 12c中，大量新的後臺程式被引入進來，很多新特性的實現都和新的程式有關。如：

1. Oracle 12c實現了多LGWR管理，這就引入了LG00-LG99一系列的後臺程式；
2. Oracle 12c擴充套件了多DBWR支援，BW36~BW99，這一列程式都會提高DBWR的寫並行；
3. Oracle 12c的多程式多執行緒模式 - MPMT，引入SCMN程式作為執行緒監聽程式；

下表對這些程式做了一定的梳理和說明，供大家參考。

程式名	全名	簡要描述	詳細描述	元件範疇
AQPC	AQ Process Coordinator	Per instance AQ global coordinator	AQPC is responsible for performing administrative tasks for AQ Master Class Processes including commands like starting, stopping, and other administrative tasks. This process is automatically started on instance startup.	Database instances Advanced Queueing
ARSn	ASM Recovery Slave Process（程式範圍 ARS0-ARS9）	Recovers ASM transactional operations	The ASM RBAL background process coordinates and spawns one or more of these slave processes to recover aborted ASM transactional operations. These processes run only in the Oracle ASM instance.	Oracle ASM instances
BWnn	Database Writer Process	Writes modified blocks from the database buffer cache to the data files	See the Long Description for the DBWn process in this table for more information about the BWnn process.	Database instances
FENC	Fence Monitor Process	Processes fence requests for RDBMS instances which are using Oracle ASM instances	CSS monitors RDBMS instances which are connected to the Oracle ASM instance and constantly doing I/Os. When the RDBMS instance terminates due to a failure, all the outstanding I/O's from the RDBMS instance should be drained and any new I/O's rejected. FENC receives and processes the fence request from CSSD.	Oracle ASM instances
GCRn	Global Conflict Resolution Slave Process	Performs synchronous tasks on behalf of LMHB	GCRn processes are transient slaves that are started and stopped as required by LMHB to perform synchronous or resource intensive tasks.	Database instances, Oracle ASM instances, Oracle RAC
IPC0	IPC Service Background Process	Common background server for basic messaging and RDMA primitives based on IPC (Inter-process communication) methods.	IPC0 handles very high rates of incoming connect requests, as well as, completing reconfigurations to support basic messaging and RDMA primitives over several transports such as UDP, RDS, InfiniBand and RC.	Oracle RAC
LDDn	Global Enqueue Service Daemon Helper Slave	Helps the LMDn processes with various tasks	LDDn processes are slave processes spawned on demand by LMDn processes. They are spawned to help the dedicated LMDn processes with various tasks when certain workloads start creating performance bottlenecks. These slave processes are transient as they are started on demand and they can be shutdown when no longer needed. There can be up to 36 of these slave processes (LDD0-LDDz).	Database instances, Oracle ASM instances, Oracle RAC
LGnn	Log Writer Worker	Writes redo log	On multiprocessor systems, LGWR creates worker processes to improve the performance of writing to the redo log. LGWR workers are not used when there is a SYNC standby destination. Possible processes include LG00-LG99.	Database instances
LREG	Listener Registration Process	Registers the instance with the listeners	LREG notifies the listeners about instances, services, handlers, and endpoint.	Database instances, Oracle ASM instances, Oracle RAC
OFSD	Oracle File Server Background Process	Serves file system requests submitted to an Oracle instance	This background process listens for new file system requests, both management (like mount, unmount, and export) and I/O requests, and executes them using Oracle threads.	Database instances, Oracle RAC
QMnn	AQ Master Class Process	Per instance per AQ Master Class Process	Each of this type of process represents a single class of work item such as AQ notification, queue monitors, and cross process.	Database instances Advanced Queueing
RM	RAT Masking Slave Process	Extracts and masks bind values from workloads like SQL tuning sets and DB Replay capture files	This background process is used with Data Masking and Real Application Testing.	Database instances
RMON	Rolling Migration Monitor Process	Manages the rolling migration procedure for an Oracle ASM cluster	The RMON process is spawned on demand to run the protocol for transitioning an ASM cluster in and out of rolling migration mode.	Oracle ASM instance, Oracle RAC
RPOP	Instant Recovery Repopulation Daemon	Responsible for re-creating and/or repopulating data files from snapshot files and backup files	The RPOP process is responsible for re-creating and repopulating data files from snapshots files. It works with the instant recovery feature to ensure immediate data file access. The local instance has immediate access to the remote snapshot file's data, while repopulation of the recovered primary data files happens concurrently. Any changes in the data are managed between the instance's DBW processes and RPOP to ensure the latest copy of the data is returned to the user.	Database instances
SAnn	SGA Allocator （SA00 ~ SAzz）	Allocates SGA	A small fraction of SGA is allocated during instance startup. The SAnn process allocates the rest of SGA in small chunks. The process exits upon completion of SGA allocation.	Database instances
SCCn	ASM Disk Scrubbing Slave Check Process	Performs Oracle ASM disk scrubbing check operation	SCCn acts as a slave process for SCRB and performs the checking operations. The possible processes are SCC0-SCC9.	Oracle ASM instances
SCRB	ASM Disk Scrubbing Master Process	Coordinates Oracle ASM disk scrubbing operations	SCRB runs in an Oracle ASM instance and coordinates Oracle ASM disk scrubbing operations.	Oracle ASM instances
SCRn	ASM Disk Scrubbing Slave Repair Process	Performs Oracle ASM disk scrubbing repair operation	SCRn acts as a slave process for SCRB and performs the repairing operations. The possible processes are SCR0-SCR9.	Oracle ASM instances
SCVn	ASM Disk Scrubbing Slave Verify Process	Performs Oracle ASM disk scrubbing verify operation	SCVn acts as a slave process for SCRB and performs the verifying operations. The possible processes are SCV0-SCV9.	Oracle ASM instances
TTnn	Redo Transport Slave Process	Ships redo from current online and standby redo logs to remote standby destinations configured for ASYNC transport	TTnn can run as multiple processes, where nn is 00 to ZZ.	Database instances, Data Guard
VUBG	Volume drive Umbilicus Background	Relays messages between Oracle ASM instance and Oracle ASM Proxy instance that is used by ADVM (for ACFS)		Oracle ASM instances, Oracle ASM Proxy instances

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About Me

........................................................................................................................ ● 本文作者：小麥苗，部分內容整理自網路，若有侵權請聯絡小麥苗刪除 ● 本文在itpub（ http://blog.itpub.net/26736162 ）、部落格園（ http://www.cnblogs.com/lhrbest ）和個人weixin公眾號（ xiaomaimiaolhr ）上有同步更新 ● 本文itpub地址： http://blog.itpub.net/26736162 ● 本文部落格園地址： http://www.cnblogs.com/lhrbest ● 本文pdf版、個人簡介及小麥苗雲盤地址： http://blog.itpub.net/26736162/viewspace-1624453/ ● 資料庫筆試面試題庫及解答： http://blog.itpub.net/26736162/viewspace-2134706/ ● DBA寶典今日頭條號地址： ........................................................................................................................ ● QQ群號： 230161599 （滿） 、618766405 ● weixin群：可加我weixin，我拉大家進群，非誠勿擾 ● 聯絡我請加QQ好友 （ 646634621 ） ，註明新增緣由 ● 於 2019-03-01 06:00 ~ 2019-03-31 24:00 在魔都完成 ● 最新修改時間：2019-03-01 06:00 ~ 2019-03-31 24:00 ● 文章內容來源於小麥苗的學習筆記，部分整理自網路，若有侵權或不當之處還請諒解 ● 版權所有，歡迎分享本文，轉載請保留出處 ........................................................................................................................ ● 小麥苗的微店 ： ● 小麥苗出版的資料庫類叢書 ： http://blog.itpub.net/26736162/viewspace-2142121/ ● 小麥苗OCP、OCM、高可用網路班 ： http://blog.itpub.net/26736162/viewspace-2148098/ ● 小麥苗騰訊課堂主頁 ： https://lhr.ke.qq.com/ ........................................................................................................................ 使用 weixin客戶端 掃描下面的二維碼來關注小麥苗的weixin公眾號（ xiaomaimiaolhr ）及QQ群（DBA寶典）、新增小麥苗weixin， 學習最實用的資料庫技術。 ........................................................................................................................