Oracle waits event:DB File Sequential Read
The DB File Sequential Read wait event generally indicates a single block read (an index read,
for example). A large number could indicate poor joining orders of tables or unselective indexing.
This number will certainly be large (normally) for a high-transaction, well-tuned system. You
should correlate this wait with other known issues within the STATSPACK report such as
inefficient SQL. Check to ensure index scans are necessary and check join orders for multiple
table joins. The DB_CACHE_SIZE will also be a determining factor in how often these waits show
up; hash-area joins causing problems should show up in the PGA memory but similarly are
memory hogs that can cause high wait numbers for sequential reads or can also show up as
direct path read/write waits. Range scans can read a lot of blocks if the data is spread in many
different blocks (density within blocks could cause issues with range scans, and reverse key
indexes could be problematic with range scans). Loading data in a sorted manner can help
range scans and reduce the number of blocks read. Partitioning can help, as it can eliminate
some blocks. Look for unselective indexes that are causing a lot of these. Locate the data on
disk systems that either have more disk caching and/or are buffered by OS file system cache.
Correlated to the waits are the values for P1,P2,P3=file, block, blocks.
相关文档：
基于OCI 实现的 最高效dump程序， 比OTL 以及其他的接口都快很多
能执行任何sql , 自动识别字段名和字段类型，进行输出输出
/*
* oracle_dump.cpp
*
* Created on: 2010-2-1
* Author: clm971910@gmail.com
*
* 压缩
* 4216351 dump done
* 完整 106 秒
* 写分隔符 8秒
* 压缩写磁 ......
--刪除重復列
a.如果有ID字段，就是具有唯一性的字段
delect table where id not in (
select max(id) from table group by col1,col ......
一：无返回值的存储过程
1、建立存储过程
CREATE OR REPLACE PROCEDURE TESTA(PARA1 IN VARCHAR2,PARA2 IN VARCHAR2) AS
BEGIN
INSERT INTO T_TEST (I_ID,I_NAME) VALUES (PARA1, PARA2);
END TESTA;
2、相应的JAVA程序
import java.sql.*;
import java.io.OutputStream;
import java.io.Writer;
import java.sq ......
输入参数：str ——要截取的字符串, ch——要查找的字符串
截取ch之前（不包括ch）的字符串： substr(str, 0, instr(str, ch) - 1)
截取ch之后（不包括ch）的字符串： substr(str, , instr(str, ch) + 1, length(str)) ......
The DB File Scattered Read wait event generally indicates waits related to full table scans or fast
full index scans. As full table scans are pulled into memory, they are scattered throughout the
buffer cache, since it is usually unlikely that they fall into contiguous buffers. A large numb ......
