Oracle's V$ Views |
v$bh This dynamic view has an entry for each block in the database buffer cache. The column status can be:
v$db_object_cache This view displays objects that are cached (pinned) in the library cache. See also dbms_shared_pool. v$event_name Contains a record for each wait event. v$lock This view stores all information relating to locks in the database. The interesting columns in this view are sid (identifying the session holding or aquiring the lock), type, and the lmode/request pair. Important possible values of type are TM (DML or Table Lock), TX (Transaction), MR (Media Recovery), ST (Disk Space Transaction). Exactly one of the lmode, request pair is either 0 or 1 while the other indicates the lock mode. If lmode is not 0 or 1, then the session has aquired the lock, while it waits to aquire the lock if request is other than 0 or 1. The possible values for lmode and request are:
If the lock type is TM, the column id1 is the object's id and the name of the object can then be queried like so: select name from sys.obj$ where obj# = id1 A lock type of JI indicates that a materialized view is being refreshed. A more detailed example can be found here See also x$kgllk. v$locked_object Who is locking what: select oracle_username os_user_name, locked_mode, object_name, object_type from v$locked_object a,dba_objects b where a.object_id = b.object_id v$log Contains information on each log group. See also online redo log. Comman values for the status column are:
v$logfile This view can be queried to find the filenames, group numbers and states of redo log files. For example, to find all files of group 2, use select member from v$logfile where group# = 2 v$log_history This view contains an entry for each Log Switch that occured. The column first_time indicates the time of the first entry??? On physical standby databases, this view shows applied logs. v$mystat This view records statistical data about the session that accesses it. Join statistic# with v$statname. See also recording statistics with oracle. v$nls_parameters The NLS parameters that are in effect for the session quering this view. The view NLS_SESSION_PARAMETERS is based on v$nls_parameters. See also v$nls_valid_values. v$nls_valid_values This view can be used to obtain valid values for NLS parameters such as
v$parameter Lists the name-value pairs of the init.ora file (or their default, if not in the init.ora). For example, if you need to know what your block size is: select value from v$parameter where name = 'db_block_size' The columns isses_modifiable and issys_modifiable can be used to determine if a parameter can be changed at session level using alter session or at system level using alter system. A parameter is modifiable at session level if isses_modifiable = 'TRUE'. A parameter is modifiable at system level if issys_modifiable = 'DEFERRED' or issys_modifiable = 'IMMEDIATE'. However, if a parameter is changed at system level if issys_modifiable = 'DEFERRED' it only affects sessions that are started after chaning the parameter. Additionally, the alter system set ... deferred option must be used. There are also some undocumented (or hidden?) parameters. v$process Join v$process's addr with v$session paddr. The column traceid is equal to the value used in alter session set . v$session The column audsid can be joined with sys_context('userenv','SESSIONID') to find out which session is the "own one". Alternatively, dbms_support.mysid can be used. The fields module and action of v$session can be set with dbms_application_info.set_module. (See v$session_longops for an example. The field client_info can be set with dbms_application_info.set_client_info Join sid with v$sesstat if you want to get some statistical information for a particular sesssion. A record in v$session contains sid and serial#. These numbers can be used kill a session (alter system kill session). A client can set some information in client_info. For example, RMAN related sessions can be found with .... where client_info like 'rman%'; What a session is waiting for can be queried with v$session_wait. However, with Oracle 10g, this is not nessessary anymore, as v$session_wait's information will be exposed within v$session as well. See also sessions. v$session_event This views is similar to v$system_event. However, it breaks it down to currently connected sessions. v$session_event has also the column max_wait that shows the maximum time waited for a wait event. v$session_longops Use v$session_longops if you have a long running pl/sql procedure and want to give feedback on how far the procedure proceeded. If the following Procedure is run, it will report its progress in v$session_longops. The Procedure will also set the module attribute in v$session which makes it possible to find the sid and serial# of the session. create table f(g number);
create or replace procedure long_proc as rindex pls_integer := dbms_application_info.set_session_longops_nohint; slno pls_integer; -- Name of task op_name varchar2(64) := 'long_proc'; target pls_integer := 0; -- ie. The object being worked on context pls_integer; -- Any info sofar number; -- how far proceeded totalwork number := 1000000; -- finished when sofar=totalwork -- desc of target target_desc varchar2(32) := 'A long running procedure'; units varchar2(32) := 'inserts'; -- unit of sofar and totalwork begin dbms_application_info.set_module('long_proc',null); dbms_application_info.set_session_longops ( rindex, slno);
for sofar in 0..totalwork loop insert into f values (sofar); if mod(sofar,1000) = 0 then dbms_application_info.set_session_longops ( rindex, slno, op_name, target, context, sofar, totalwork, target_desc, units); end if; end loop; end long_proc; If the procedure long_proc is run, you can issue the following query to get feedback on its progress: select time_remaining,sofar,elapsed_seconds from v$session_longops l, v$session s where l.sid=s.sid and l.serial# = s.serial# and s.module='long_proc' v$session_wait This views shows what wait event each session is waiting for, or what the last event was that it waited for. The columns P1, P2 and P3 are parameters that are dependant on the event. With Oracle 10g, v$session_wait's information will be exposed within v$session as well. Since 10g, Oracle displays the v$session_wait information also in the v$session view. v$session_wait_history This view is new in Oracle 10g and allows improved timing and statistics. v$sesstat This view is similar to v$mystat except that it shows cumulated statistics for all sessions. Join sid with v$session and join statistic# with v$statname. v$sesstat is also similar to v$sysstat, except that v$sysstat accumulates the statistics as soon as a session terminates. v$sga Shows how much memory the shared global area uses. Select * from v$sga is roughly the same as typing show sga in sql plus with the exeption that the latter also show the total. v$sgastat Showing free space in the sga: select * from v$sgastat where name = 'free memory' v$sql v$sql is similar to v$sqlarea, the main difference being that v$sql drills down to select * from x$kglob whereas v$sqlarea drills down to select sum from x$kglob. See also here. v$sqlarea Join v$sqlarea's address with v$session's sql_address. Find the SQL-text of currently running SQL statements: select sql_text from v$sqlarea where users_executing > 0; The field version_count indicates how many versions an sql statement has. v$sql_plan variable addr varchar2(20) variable hash number variable child number
exec :addr := '&sqladdr'; :hash := &hashvalue; :child := &childno;
select lpad(' ', 2*(level-1))||operation||' '|| decode(id, 0, 'Cost = '||position) "OPERATION", options, object_name from v$sql_plan start with (address = :addr and hash_value = :hash and child_number = :child and id=0 ) connect by prior id = parent_id and prior address = address and prior hash_value = hash_value and prior child_number = child_number order by id, position ; In order to find valid values for sqladdr, hashvalue and childno, this SQL statement can be used: select sql_text,address,hash_value,child_number from v$sql where users_executing > 0; v$sqltext_with_newlines This view can be used to construct the entire text for each session's actual SQL statement. Use the following statement to to that: set serveroutput on size 1000000
declare v_stmt varchar2(16000); v_sql_text v$sqltext_with_newlines.sql_text%type; v_sid v$session.sid%type; begin for r in ( select sql_text,s.sid from v$sqltext_with_newlines t, v$session s where s.sql_address=t.address order by s.sid, piece) loop v_sid := nvl(v_sid,r.sid); if v_sid <> r.sid then dbms_output.put_line(v_sid); put_line(v_stmt,100); v_sid := r.sid; v_stmt := r.sql_text; else v_stmt := v_stmt || r.sql_text; end if; end loop; dbms_output.put_line(v_sid); dbms_output.put_line(v_stmt,100); end; / v$sql_cursor Join parent_handle with address of v$sql or v$sqlarea. v$sql_workarea v$sql_workarea can be joined with v$sqlarea on address and hash_value, and it can be joined with v$sql on address, hash_value and child_number. v$sysstat v$sysstat is similar to v$sesstat. While v$sesstat displays statitics for the current session, v$sysstat displays the cumulated statitics since startup of the database. For example, it is possible to find out the CPU time (name = 'CPU used by this session') This view is (among others) used to calculate the Hit Ratio. v$system_event This view displays the count (total_waits) of all wait events since startup of the instance. If timed_statistics is set to true, the sum of the wait times for all events are also displayed in the column time_waited. The unit of time_waited is one hundreth of a second. Since 10g, an additional column (time_waited_micro) measures wait times in millionth of a second. total_waits where event='buffer busy waits' is equal the sum of count in v$waitstat. v$enqueue_stat can be used to break down waits on the enqueue wait event. While this view totals all events in an instance, v$session_event breaks it down to all currently connected sessions. v$transaction Important fields of v$transaction are used_ublk and used_urec. They tell of how many blocks and records the undo for a transaction consists. In order to find out the name of the corresponding rollback segemnt, join the xidusn field with the usn field of v$rollname. This is demonstrated in Transactions generate undo v$waitstat total_waits where event='buffer busy waits' is equal the sum of count in v$system_event.
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