oracle备忘

一、explain plan

a)explain plan for select ...

select * from table(dbms_xplan.display());

function display (table_name   varchar2 default 'PLAN_TABLE',
                  statement_id varchar2 default null,
                  format       varchar2 default 'TYPICAL')

- table_name:
      specifies the table name where the plan is stored. This
      parameter defaults to "PLAN_TABLE" which is the default
      plan table for the explain plan.

- statement_id:
      specifies the statement id of the plan to display. This
      parameter defaults to NULL.

- format:
     'BASIC':   Display only the minimum, i.e. the operation id, 
                the operation name and its option
     'TYPICAL': This is the default. Display most information
                of the explain plan (operation id, name and option,
                #rows, #bytes and optimizer cost. Pruning, 
                parallel and predicate information are only 
                displayed when applicable.
     'ALL':     Maximum level. Like typical with additional display
                of the SQL statements generated for PX servers
                (only if parallel). 
     'SERIAL':  Like typical except that parallel information are
                  not displayed, even if the plan is parallel

b)dbms_xplan.display_awr(sql_id VARCHAR2,
plan_hash_value INTEGER DEFAULT NULL,
db_id           INTEGER DEFAULT NULL,
format          VARCHAR2 DEFAULT 'TYPICAL')
RETURN dbms_xplan_type_table PIPELINED;

c)dbms_xplan.display_cursor(
sql_id          VARCHAR2 DEFAULT NULL,
cursor_child_no INTEGER DEFAULT 0,
format          VARCHAR2 DEFAULT 'TYPICAL')
RETURN dbms_xplan_type_table PIPELINED;

select child_number from v$sql_shared_cursor where sql_id='...';

d)dbms_xplan.display_sqlset(
sqlset_name     VARCHAR2,
sql_id          VARCHAR2,
plan_hash_value INTEGER DEFAULT NULL,
format          VARCHAR2 DEFAULT 'TYPICAL',
sqlset_owner    VARCHAR2 DEFAULT NULL)
RETURN dbms_xplan_type_table PIPELINED;

2、v$sql_shared_cursor的reason为OPTIMIZER_MISMATCH—优化器环境与现有的子游标不匹配时括号中的数字意义
1 = Degree used is not the default DOP
2 = In (RAC) cases where instance count is not the same, or session CPU count is not the same, or thread count is not the same
3 = _parallel_syspls_obey_force is FALSE
4 = The PQ mode does not match.
5 = The degree does not match.
6 = The parallel degree policy does not match.
7 = The session limit is not the same as the cursor limit but the cursor limit is the same as the degree used.
8 = The cursor limit is greater than the degree used and the session limit is less than the cursor limit
9 = The cursor limit is less than the degree used and the session limit is not the same as the cursor limit
10 = Optimizer mode difference
11 = Materialized View mismatch
12 = Optimizer environment mismatch (ie an optimizer parameter is different)
13 = Cardinality Feedback is use

二、sqlplus启动执行命令

[$ORACLE_HOME/sqlplus/admin,$SQLPATH,.]\glogin.sql,login.sql

显示所有参数

show all

show user,show error

三、sql多行结果转一行

select i,wmsys.wm_concat(a) from t group by i;

四、当前session_id

select sid, serial#, status from v$session where audsid=userenv('sessionid');

select sid from v$mystat where rownum=1;

select userenv('sid') from dual;

五、flashback

db_recovery_file_dest：指定闪回恢复区的位置
db_recovery_file_dest_size：指定闪回恢复区的可用空间大小
db_flashback_retention_target：指定数据库可以回退的时间，单位为分钟，默认1440分钟，也就是一天。

v$flash_recovery_area_usage:    flash_recovery_area空间使用情况（分类）

v$recovery_file_dest：　　空间使用

dba_outstanding_alerts:空间告警

V$CONTROLFILE, V$LOGFILE, V$ARCHIVED_LOG, V$DATAFILE_COPY 等数据字典的列IS_RECOVERY_DEST_FILE ,指明相关的文件是否在恢复区内

六、数据字典

select reason,object_type,suggested_action,creation_time from dba_outstanding_alerts;
性能、资源相关告警，补充alert
select * from v$resource_limit;
资源使用历史

七、闪回查询

利用undo

当前scn
select to_char(sysdate, 'yyyy-mm-dd hh24:mi:ss') time, to_char(dbms_flashback.get_system_change_number) scn from dual;
Scn转换成时间：
select to_char(scn_to_timestamp(3998591352171),'YYYY-MM-DD HH24:MI:SS') from dual；
时间转换成scn：
select timestamp_to_scn(to_date('2011-04-14 11:10:25','YYYY-MM-DD HH24:MI:SS')) from dual；
查询该时间点（或scn）的数据，如下：
select * from t as of timestamp to_timestamp('2000-01-01 01:01:01', 'yyyy-mm-dd hh24:mi:ss');
select * from t as of scn xxx;