这部分目前主要是从网上搜集来的，后续要在实践中慢慢体会。

v$sqltext: 存储的是被分割的sql
v$sqlarea: 存储的是完整的sql和一些统计信息，比如累计的执行次数、逻辑读、物理读等（统计）
v$sql: 内存共享sql区域中已经解析的完整sql语句（即时）

--查看当前性能瓶颈，sid=session id, spid=server process id, paddr=process address
select * from v$mystat where rownum = 1 --sid
select * from v$session where sid = 1014 --paddr
select * from v$process where addr = '36C30CDC'

--查看锁对象，并杀会话
select * from v$locked_object --查看锁对象的session_id
select * from v$session where sid in (191, 100)
alter system kill session '191,2025' --sid, serial# 杀会话

--查询最慢的sql，根据磁盘读的次数
select * from (
select parsing_user_id,executions,sorts
command_type,disk_reads,sql_text from v$sqlarea order by disk_reads desc
)where rownum<10

--查询对应session，根据物理读
select SE.SID,SE.SERIAL#,PR.SPID,
SE.USERNAME,SE.STATUS,SE.TERMINAL,
SE.PROGRAM,SE.MODULE,
SE.SQL_ADDRESS,ST.EVENT,
ST.P1TEXT,SI.PHYSICAL_READS,SI.BLOCK_CHANGES from v$session se,v$session_wait st,
v$sess_io si,v$process pr
where st.SID=se.SID and st.SID=si.SID
AND SE.PADDR=PR.ADDR
AND SE.SID>6
AND ST.WAIT_TIME=0
AND ST.EVENT NOT LIKE '%SQL%'
ORDER BY PHYSICAL_READS DESC;
SELECT sql_address FROM V$SESSION SS,V$SQLTEXT TT
WHERE SS.SQL_HASH_VALUE=TT.HASH_VALUE AND SID=439;

--根据sid查找完整sql语句：
select sql_text from v$sqltext a where a.hash_value = (select sql_hash_value from v$session b where b.sid = '&sid')
order by piece asc

select a.CPU_TIME,--CPU时间 百万分之一（微秒）
a.OPTIMIZER_MODE,--优化方式
a.EXECUTIONS,--执行次数
a.DISK_READS,--读盘次数
a.SHARABLE_MEM,--占用shared pool的内存多少
a.BUFFER_GETS,--读取缓冲区的次数
a.COMMAND_TYPE,--命令类型(3:select,2:insert;6:update;7delete;47:pl/sql程序单元)
a.SQL_TEXT,--Sql语句
a.SHARABLE_MEM,
a.PERSISTENT_MEM,
a.RUNTIME_MEM,
a.PARSE_CALLS,
a.DISK_READS,
a.DIRECT_WRITES,
a.CONCURRENCY_WAIT_TIME,
a.USER_IO_WAIT_TIME
from SYS.V_$SQLAREA a
WHERE PARSING_SCHEMA_NAME = 'CHEA_FILL'--表空间
order by a.CPU_TIME desc

--从V$SQLAREA中查询最占用资源的查询，用buffer_gets列来替换disk_reads列可以得到占用最多内存的sql语句的相关信息
select b.username username,a.disk_reads reads,
a.executions exec,a.disk_reads/decode(a.executions,0,1,a.executions) rds_exec_ratio,
a.sql_text Statement
from v$sqlarea a,dba_users b
where a.parsing_user_id=b.user_id
and a.disk_reads > 100000
order by a.disk_reads desc;

--列出使用频率最高的5个查询：
select sql_text,executions
from (select sql_text,executions,
rank() over
(order by executions desc) exec_rank
from v$sql)
where exec_rank <=5;

--消耗磁盘读取最多的sql top5：
select disk_reads,sql_text
from (select sql_text,disk_reads,
dense_rank() over
(order by disk_reads desc) disk_reads_rank
from v$sql)
where disk_reads_rank <=5;

--找出需要大量缓冲读取（逻辑读）操作的查询：
select buffer_gets,sql_text
from (select sql_text,buffer_gets,
dense_rank() over
(order by buffer_gets desc) buffer_gets_rank
from v$sql)
where buffer_gets_rank<=5;