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soft parse and hard parse！ （from jl）
When you submit an SQL statement for processing, it passes through a number of stages before your server process finally gets to execute it and give you back the results. First your command is checked for syntax errors - basically, is the command correctly formed ? If the syntax check is passed, it is checked for semantic errors - things like do all the objects required exist, does the user have appropriate privileges etc. The next stage is to pass the command thorough a hashin
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Cache Header and Tail (转载 ixora)
All datafile blocks are written and read by the cache layer of the Oracle kernel (KCB) generally through the database buffer cache. The cache layer reads and maintains a 20-byte header and 4-byte tail on each data block, called the cache header and tail. The cache header is called the common block header in V$TYPE_SIZE and elsewhere. Controlfile blocks also have a cache header and tail, although not all the fields are used. This is what the cache header and tail look like in a data
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bbed 安装
cd $ORACLE_HOME/rdbms/lib ls -al *bb*.o -rw——- 1 oracle dba 3152 Nov 7 2006 sbbdpt.o -rw——- 1 oracle dba 2424 Nov 7 2006 ssbbded.o make -f ins_rdbms.mk $ORACLE_HOME/rdbms/lib/bbed [oracle@rhel4u5 lib]$ ls -l *bb* -rwxr-xr-x 1 oracle oinstall 554330 12月 23 23:09 bbed -rw-r--r-- 1 oracle oinstall 3124 2008-02-16 sbbdpt.o -rw-r--r-- 1 oracle oinstall 2802 2008-02-16 ssbbded.o cp $ORACLE_HOME/rdbms/lib/bbed $ORACLE_HOME/bin bbed Password: <
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闲聊存储产品各种性能差异区别(转载)
闲聊存储产品各种性能差异区别说起存储产品的评价，性能永远是第一重要的问题。吹嘘性能的各种说辞在供应商口中不断花样翻新：带宽（Bandwidth）、IOPS、顺序（Sequential）读写、随机（Random）读写、持续吞吐（Sustained Throughput）、突发处理能力（Burst I/O）等等看似甚为专业的名词充斥着解决方案和技术分析报告。存储产品的性能似乎被量化得格外清晰，作为用户，只需要简单的比较两个数字，就可以清楚的得出孰优孰劣的结论。然而，事实果真如此吗？让我们先来看几个有趣的实例。在Engenio公司的网站上，很容易就可以分辩出4884控制
