SQL MOnitoring.doc

7/29/2019 SQL MOnitoring.doc

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Problem - find blocking sessions

Recipie #1 - find blocking sessions with v$session

SELECTs.blocking_session,s.sid,s.serial#,s.seconds_in_wait

FROMv$session s

WHEREblocking_session IS NOT NULL

Recipie #2 - find blocking sessions using v$lock

SELECTl1.sid || ' is blocking ' || l2.sid blocking_sessions

FROMv$lock l1, v$lock l2

WHEREl1.block = 1 ANDl2.request > 0 AND

l1.id1 = l2.id1 ANDl1.id2 = l2.id2

Recipie #3 - blocking sessions with all available information

SELECT s1.username || '@' || s1.machine|| ' ( SID=' || s1.sid || ' ) is blocking '|| s2.username || '@' || s2.machine || ' ( SID=' || s2.sid || ' ) ' AS blocking_statusFROM v$lock l1, v$session s1, v$lock l2, v$session s2WHERE s1.sid=l1.sid AND s2.sid=l2.sidAND l1.BLOCK=1 AND l2.request > 0AND l1.id1 = l2.id1AND l2.id2 = l2.id2 ;

Recipie #4 - identifying blocked objects

The following queries shows you all the TM locks:

SELECT sid, id1 FROM v$lock WHERE TYPE='TM'SID ID1

The ID you get from this query refers to the actual database object which can help you to identify theproblem, look at the next query:

SELECT object_name FROM dba_objects WHERE object_id=20127

There queries should help you to identify the cause of your blocking sessions!

Problem - Finding Oracle Session ID (SID)The current Oracle session ID is often used when you want to analyze data from v$session and similar views.

Recipie #1 - Finding the Oracle Session IDThere are several ways to get the Oracle session ID, here's the probably most used version:

SELECT SYS_CONTEXT('USERENV', 'SID') FROM DUAL;

Recipie #2 - combining Session ID and v$session


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Here's a simple example showing you how to use the current session ID in combination with v$session:

SELECT osuser, programFROM v$sessionWHERE sid=SYS_CONTEXT('USERENV', 'SID');

Recipe #3 - alternative ways to get session ID

just in case you wonder, there are more ways to get the current session ID:

SELECT sidFROM v$mystatWHERE ROWNUM = 1;

Problem - Finding locked database object

SELECT DO.owner,DO.object_name,DO.object_type,lo.session_id,lo.oracle_username

FROM dba_objects DO, v$locked_object loWHERE DO.object_id = lo.object_id

Show long running SQL Statements

SELECT s.username,sl.sid,sq.executions,sl.last_update_time,sl.sql_id,sl.sql_hash_value,opname,target,elapsed_seconds,time_remaining,sq.sql_fulltext

FROM v$session_longops slINNER JOIN v$sql sq ON sq.sql_id = sl.sql_idINNER JOIN v$session s ON sl.SID = s.SID AND sl.serial# = s.serial#WHERE time_remaining > 0

Get details about long running operations

SELECT osuser,sl.sql_id,sl.sql_hash_value,opname,target,elapsed_seconds,

time_remainingFROM v$session_longops slinner join v$session s ON sl.SID = s.SID AND sl.SERIAL# = s.SERIAL#WHERE time_remaining > 0

Determine Database Uptime

Recipe #1 - Query v_$instance to get the uptime


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SELECT host_name,instance_name,TO_CHAR(startup_time, 'DD-MM-YYYY HH24:MI:SS') startup_time,FLOOR(sysdate-startup_time) days

FROM sys.v_$instance;This query will return some additional information like the host and database instancename as well as the number of days the database is running in the last column.

Recipe #2 - Query v$session to get database uptime

You'll often see articles telling you to query the session with SID 1, but this won't work everywhere. Thefollowing query seems to be more reliable, it checks the process with the name PMON, which is part of thedatabase and reads its logon time:

SELECT TO_CHAR(logon_time, 'DD-MM-YYYY HH24:MI:SS')FROM v$sessionWHERE program LIKE '%PMON%'

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SQL MOnitoring.doc