blocking lock killer - cohesion nashville 2013

Presented by: Shawn Lee, University of Illinois

Monday, November 4, 2013Session #149

Blocking Lock Killer

co•he•sion noun \kō-ˈhē-zhən\ 1 : the act or state of sticking together tightly; especially: unity

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TopicsDatabase transactions and locking mechanisms

Blocking locks in Banner

Monitoring & triaging blocking locks

University of Illinois’ blocking lock killer tool

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Audience Participation Test!

Overview of database transactions and locking mechanisms

Concepts

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What is a transaction?A single execution within the database

A series of reads and writes of database objects

Final action – commit or abort

Committed transactions must be durable

Aborted transactions must be undone

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ACIDTransactions have four essential properties:

1) atomicity

2) consistency

3) isolation

4) durability

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Motivation for ConcurrencyTransactions can be executed in serial, but…that’s ineffiecient

DBMS improves performance by interleaving the actions of different transactions so they can run concurrently

Only serializable schedules are generated

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Issues with ConcurrencyThree problems that can arise:

Dirty Reads (WR conflict) – a transaction reads a value written by another uncommitted transaction

Unrepeatable Reads (RW conflict) – a transaction reads the value of the same object twice; another transaction modifies that value in between the two reads

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Issues with Concurrency (cont.)Lost Updates (WW conflict) – Two transactions update the value of the same object, before either of them have committed

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Data Locking MechanismsShared Locks – acquired when reading data without making modifications; shared with other transactions that only need to read, not write

Exclusive Locks – acquired when modifying data, prevents any other transaction from accessing the data

The amount of data locked can vary

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More on lockingTwo-Phase Locking (2PL) – common protocol used to make it easier for DBMS to schedule serializable transactions

# of locks acquired by transaction grows (phase 1) then shrinks (phase 2)

Deadlocks – when two transactions are stuck waiting on each other; Oracle detects and handles these automatically

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Database Locks in BannerCauses of blocking locks and their

effects

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The effect of locks in BannerDatabase locks are commonLocks can last for seconds, minutes, or hours depending on what the root blocker is doingThe “blocker” and “blockee” could be a batch job, or a user.If the blockee is a user, an extensive lock can result in a poor experience

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Common CausesUsers blocking themselves

SOAHOLD (placing student holds)PEALEAV (employee leave balances/accruals)FZAREQN (custom form for multiyear POs)

Peak processing times (start of term activities, grade roll, payroll deduction runs)

Scheduled jobs (Appworx, a.k.a. UC4)

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Triaging Blocking LocksHow we handle them

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It starts with active monitoringHP SiteScopeselect count(*) from v$session a, v$session b where 10 <= round(a.seconds_in_wait/60,1) and a.blocking_session_status = 'VALID’ and a.wait_class = 'Application’ and a.blocking_session=b.sid and b.username not like 'APPWORX%'

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Our triage processMagic number = 10 minutesIdentify the root blockerDuring business hours, call user firstIf can’t make phone contact, kill sessionExtra care for jobsub processesSelf-service sessions killed immediatelyOutside business hours, kill immediately then communicate immediately

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After the killThe database rolls back the transaction

User may lose work

Forms users screen may go blank and/or they will get network errors

Impact to self-service users will be less due to web session persistence

Communication and follow-up are keyCoHEsion Summit

The Tool The old and the new

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The Old Tool

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The Old Tool (cont.)

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The New Tool

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Session Table

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Contact Info

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Details and Kill Now options

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Session Details

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After the Kill

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Tool Permissions

WebTailor user roles

System Admin – Can Kill Sessions

System Monitor – “Kill” option not visible

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Database procedures-- FILE NAME..: pkg_banner_monitoring_tools.pkg-- OBJECT NAME: UILLINOIS.pkg_banner_monitoring_tools-- USAGE......: Banner monitoring tools, including new blocking lock utility to replace the blocking lock utility from the-- Triage site that was written by Mike Cornell

procedure P_ShowSessionDetails (sid_in IN v$session.sid%TYPE, serial_in IN v$session.serial#%TYPE);

procedure P_ShowSessionsAndBlocks (dispinfo IN VARCHAR2 DEFAULT 'DEFAULT');

procedure P_KillSession (sid_in IN v$session.sid%TYPE, serial_in IN v$session.serial#%TYPE, username_in IN v$session.username%TYPE);

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Noteworthy components

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Database cursor – blocker and blockee information in each rowV$LOCK, V$SESSION, V$PROCESSContact info retrieved from GOBEACC, SPRIDEN, SPRTELE, SPRADDR, GOREMAL

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Noteworthy components

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Row coloring:CASE WHEN rblock.blockee_minutes_in_wait > 10 THEN rowcolor:='#FF0000'; --red WHEN rblock.blockee_minutes_in_wait > 3 THEN rowcolor:='#F4FA58'; --yellow ELSE rowcolor:='#80FF00'; --greenEND CASE;htp.tableRowOpen(cattributes=>'bgcolor="' || rowcolor || '"');

Control display of “Kill” link:if twbkwbis.f_validlink('pkg_banner_monitoring_tools.P_KillSession') then

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Noteworthy components

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Page refresh:twbkwbis.P_OpenDoc ('pkg_banner_monitoring_tools.P_ShowSessionsAndBlocks', refresh_delay => 30, refresh_url => OWA_UTIL.get_cgi_env ('REQUEST_PROTOCOL') || '://' || OWA_UTIL.get_cgi_env ('HTTP_HOST') || ':' || OWA_UTIL.get_cgi_env ('SCRIPT_NAME') || '/pkg_banner_monitoring_tools.P_ShowSessionsAndBlocks' );

Result = https://ui2web1.apps.uillinois.edu/BANPROD1/pkg_banner_monitoring_tools.P_ShowSessionsAndBlocks

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Noteworthy components

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Kill session: oracle.killsession(sid_in,serial_in,username_in,dbname,result); -- check the result CASE WHEN result LIKE '%auditname parameter not provided%' THEN P_ShowSessionsAndBlocks('NOKILL_NODB'); WHEN result LIKE '%This is a privileged ID%' THEN P_ShowSessionsAndBlocks('NOKILL_PRIVID'); WHEN result LIKE '%did not match with username%' THEN P_ShowSessionsAndBlocks('NOKILL_USRMTCH'); WHEN result LIKE '%alter system kill session%' THEN P_ShowSessionsAndBlocks('KILLED'); END CASE;

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Poll

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Thank You!

Shawn Lee, University of Illinoislee13@uillinois.edu

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Session ID #149

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