June 11, 2008
关于Oracle学习以及DBA工作机会
作者:eygle
出处:http://blog.eygle.com
最近有很多朋友发邮件或者在QQ/MSN上向我咨询关于学习和工作方面的问题，很多问题具有重复性，现在在这里列举一些并表达一下我的看法，希望对朋友们有益。
从朋友们的提问来看，接触Oracle的群体有极大的年轻化趋势。很多大学的学生已经开始向我咨询，这在以前是不常见的，现在的学生能够更早的接触Oracle，这真是一件好事。
有很多朋友在自学Oracle，并且希望能够转向DBA的工作，那么怎样来完成这个过程呢？很多人对此迫不及待。
以下是一个朋友的来信，他的一些想法很有代表性：
2007年1月正式参加工作，原来一直做java开发，
然后因公司需要做维护。随着接触数据库渐多，对数据库产生了兴趣。
2007年11月至今一直在学习数据库，...也慢慢的入门了，准备完全从事数据库。....
问题是我现在还没有找到适合我的工作。...
很多朋友在进行了一段时间的学习之后，对转型迫不及待甚至焦虑不堪，这是不对的，在工作中应当切忌浮躁，我经常这样提醒年轻的朋友。
我们每个人从毕业到工作、再到找到适合自己的位置，这通常都要经过一个较长的时期，学习、思考、进步、再次出发，所以要知道有时候等待是过程的必须。
在我熟悉的圈子里，绝大多数资深DBA都经过过这样一个过程，很多人都是先做开发工作，然后接触Oracle、对Oracle感兴趣并开始研究、找到机会进行转型，这个过程以前都需要2～3年的时间。
我本人毕业之后也做了三年的开发工作，然后才转向DBA工作的。
而现在的年轻人，很多人一毕业就开始寻找DBA的工作，我承认现在一个DBA的成长历程被大幅缩短，但是要知道，一个人从毕业到成长为具有稳定职业发展观，总需要一个过程，在这个过程中，要保持冷静，拒绝浮躁。
如果你手上已经有了一份工作，那你需要做的是，做好它，哪怕那不是你喜欢的！
你必须证明给别人看你有做好一件事情的能力，别人才会给你下一个机会，如果你从来没能很好的完成一项任务，那你应该冷静的反省一下。
总结一下，在以上我想说的是，十年磨一剑，有时候你的等待是必须的历程，正视这个历程，珍重这个历程才是正确的态度。
我上面说，十年磨一剑，在这个历程中，你应当一直在琢磨，使自己成长，具备进一步跳跃的素质，如果你喜欢Oracle，那你应当在这个阶段完成积累过程。很多人经常是偶然有一天头脑发热，说我要去搞Oracle，这未尝不可，不过没有积累，你的起步要困难得多。
在具备了一定的积累之后，你需要的其实是机会，机会在哪里？
机会喜欢光顾有准备的头脑，你做好准备之后，静静的去寻找和等待机会，这是你应该做的。
很少有机会会从天而降，降临到毫无准备的人头上，如果你希望获得机会，那机会也希望你准备充分。
学习是没有止境的，在工作中认真处理遇到的问题，从每一个可能遇到的问题入手，深入再深入，这是对现实的把握。把握好现实才能把握未来。
去除浮躁，认真学习，不断积累，寻找机遇，这是我给很多朋友的建议。
-The End-
Posted by eygle at 8:14 PM | Comments (16)
Oracle 10g RAC的相关概念
作者:eygle
出处:http://blog.eygle.com
Oracle的Clusterware和管理组件：
Oracle Clusterware is designed for, and tightly integrated with, Oracle RAC.
When you create an Oracle RAC database using any of the management tools, the database is registered with and managed by Oracle Clusterware, along with the other Oracle processes such as Virtual Internet Protocol (VIP) address, Global Services Daemon (GSD), the Oracle Notification Service (ONS), and the Oracle Net listeners. These resources are automatically started when Oracle Clusterware starts the node and automatically restarted if they fail. The Oracle Clusterware daemons run on each node.
Oracle ClusterWare的进程组件：
Cluster Synchronization Services (CSS)--Manages the cluster configuration by controlling which nodes are members of the cluster and by notifying members when a node joins or leaves the cluster. If you are using third-party clusterware, then the css process interfaces with your clusterware to manage node membership information.
Cluster Ready Services (CRS)--The primary program for managing high availability operations within a cluster. Anything that the crs process manages is known as a cluster resource which could be a database, an instance, a service, a Listener, a virtual IP (VIP) address, an application process, and so on. The crs process manages cluster resources based on the resource's configuration information that is stored in the OCR. This includes start, stop, monitor and failover operations. The crs process generates events when a resource status changes. When you have installed Oracle RAC, crs monitors the Oracle instance, Listener, and so on, and automatically restarts these components when a failure occurs. By default, the crs process makes five attempts to restart a resource and then does not make further restart attempts if the resource does not restart.
Event Management (EVM)--A background process that publishes events that crs creates.
Oracle Notification Service (ONS)--A publish and subscribe service for communicating Fast Application Notification (FAN) events.
RACG--Extends clusterware to support Oracle-specific requirements and complex resources. Runs server callout scripts when FAN events occur.
Process Monitor Daemon (OPROCD)--This process is locked in memory to monitor the cluster and provide I/O fencing. OPROCD performs its check, stops running, and if the wake up is beyond the expected time, then OPROCD resets the processor and reboots the node. An OPROCD failure results in Oracle Clusterware restarting the node. OPROCD uses the hangcheck timer on Linux platforms.
Unix系统Oracle Clusterware的后台进程:
crsd--Performs high availability recovery and management operations such as maintaining the OCR and managing application resources. This process runs as the root user, or by a user in the admin group on Mac OS X-based systems. This process restarts automatically upon failure.
evmd--Event manager daemon. This process also starts the racgevt process to manage FAN server callouts.
ocssd--Manages cluster node membership and runs as the oracle user; failure of this process results in cluster restart.
oprocd--Process monitor for the cluster. Note that this process only appears on platforms that do not use vendor clusterware with Oracle Clusterware.
Oracle RAC的Cache Fusion技术：
Oracle RAC databases have two or more database instances that each contain memory structures and background processes.
Each instance has a buffer cache in its System Global Area (SGA). Using Cache Fusion, Oracle RAC environments logically combine each instance's buffer cache to enable the instances to process data as if the data resided on a logically combined, single cache.
The SGA size requirements for Oracle RAC are greater than the SGA requirements for single-instance Oracle databases due to Cache Fusion.
GCS和GES服务与GRD的作用：
To ensure that each Oracle RAC database instance obtains the block that it needs to satisfy a query or transaction, Oracle RAC instances use two processes, the Global Cache Service (GCS) and the Global Enqueue Service (GES). The GCS and GES maintain records of the statuses of each data file and each cached block using a Global Resource Directory (GRD). The GRD contents are distributed across all of the active instances, which effectively increases the size of the SGA for an Oracle RAC instance.
Cache Fusion的实现：
After one instance caches data, any other instance within the same cluster database can acquire a block image from another instance in the same database faster than by reading the block from disk. Therefore, Cache Fusion moves current blocks between instances rather than re-reading the blocks from disk. When a consistent block is needed or a changed block is required on another instance, Cache Fusion transfers the block image directly between the affected instances. Oracle RAC uses the private interconnect for interinstance communication and block transfers. The GES Monitor and the Instance Enqueue Process manages access to Cache Fusion resources and enqueue recovery processing.
RAC实现的几个后台进程：
The Oracle RAC processes and their identifiers are as follows:
LMS--Global Cache Service Process
LMD--Global Enqueue Service Daemon
LMON--Global Enqueue Service Monitor
LCK0--Instance Enqueue Process
Posted by eygle at 2:54 PM | Comments (9)