trouble shooting and maintenance pertemuan 13

Trouble Shooting and MaintenancePertemuan 13

Matakuliah : T0413Tahun : 2009

Bina Nusantara University 3

Problem Diagnosis

Review the DB2 online manuals

(Information Center)

Problem!

db2 ? <code>

Check the DB2 Express-C forum

Review Admin notification log

or the db2diag.log

Search for APARs, or known problems

Review system with Operating System

commands


db2 help: ?

db2 ? SQL0104Ndb2 ? SQL104Ndb2 ? SQL-0104db2 ? SQL-104db2 ? SQL-104N


Finding More Information About Error Codes• To find out more information about an error code received,

in the Command Editor input area, enter the code prefixed by a question mark and click the Execute button

Prefix error code by a question mark in the Input area

More information about the error code appears in the Output area


The DB2 Information Center

• The DB2 Information Center contains the DB2 online manuals. It also includes the manuals of products related to DB2.

• It has a search field

• It can be installed locally, or accessed through the internet

• The internet version is the most up-to-date one. The URLs are:– V9:

http://publib.boulder.ibm.com/infocenter/db2luw/v9/index.jsp– V9.5:

http://publib.boulder.ibm.com/infocenter/db2luw/v9r5/index.jsp

• Most of the answers to your questions can be found from the DB2 Information Center!


Log with diagnosis information at the point failure On Linux/UNIX platforms, the administration notification log is a text file called instance.nfy

On Windows, all administration notification messages are written to the Event Log, or you can see in in the DB2 Journal

The DBM configuration parameter notifylevel specifies the level of information to be recorded:

ƒ 0 -- No administration notification messages captured (not recommended)ƒ 1 -- Fatal or unrecoverable errorsƒ 2 -- Immediate action requiredƒ 3 -- Important information, no immediate action required (default)ƒ 4 -- Informational messages

DB2 Administration Notification Log


Information included in the db2diag.log The timestamp when the error occurred. Use it to find the error quickly The application name and DB2 function involved in the problem. A diagnostic message explaining the reason for the error. Any available supporting data, such as SQLCA data structures and

pointers to the location of any extra dump or trap files.

If you can recreate the problem: Remove/rename the db2diag.log Recreate the problem. A new db2diag.log file will be generated

db2diag.log


Example of a db2diag.log entryTimestamp when the problem occurred

Level: Be concerned when you see“Severe” or “Error” here.

Application name

Error message information. Use any of these for searching in “Google”


WIN XP/2003 (default) C:\Documents and Settings\All Users\Application Data\IBM\DB2\DB2COPY1\<instance name>

ƒ WIN VISTAƒ ProgramData\IBM\DB2\

Linux/UNIX (default) INSTHOME/sqllib/db2dump (INSTHOME is the home directory of the instance owner)

You can change the location of the db2diag.log using diagpath in the dbm cfgƒ db2 update dbm cfg using diagpath <path>

The verbosity of diagnostic text is determined by diaglevel in the dbm cfgƒ range is 0 to 4 (default is 3)ƒ most verbose is 4

Locating the db2diag.log


Free community assistancewww.ibm.com/developerworks/forums/dw_forum.jsp?forum=805&cat=19

Mainly in English

The IBM DB2 Express-C team monitors the forum, though it is the community who assists the most

You can also access it from the DB2 Express-C web site:www.ibm.com/db2/express

(and click the button to go to the forum)

The DB2 Express-C Forum

http://www.ibm.com/developerworks/forums/dw_forum.jsp?forum=805&cat=19

http://www.ibm.com/db2/express


REORG, RUNSTATS, REBIND

RUNSTATS

REBIND

REORG

Maintenance Utilities


Database Operational View in Control Center


Table Reorganization (REORG)• Over time, tables and indexes get fragmented (much like a file

system)• A REORG reclaims wasted space and re-organizes data to make

retrieval more efficient• Tables that are modified the most will benefit the most from REORGs• REORG has an Online and Offline option

– Offline REORG is faster and more efficient, but does not permit access to the table

– Online REORG allows access to the table, but can consume a lot of system resources; it works best for small tables

REORG TABLE <tablename>

Example: REORG TABLE employee


Statistics (RUNSTATS)• Keeps database statistics up-to-date

– e.g. number of rows in a table, index size, data value ranges, etc.

• Statistics are used by DB2 whenever queries are executed– DB2 Query Optimizer is a cost-based optimizer– Analyzes these statistics to produce data access plan

• The frequency of statistics gathering should be determined by how often the data in the table changes

RUNSTATS ON TABLE <schema.tablename>

Example: RUNSTATS ON TABLE myschema.employee


RUNSTATS and REORG from the Control Center

Control Center > (expand) All Databases folder > (expand) Database > (select) Tables Folder > (right-click) Table > Reorganize/Run Statistics


Bind/Rebind Packages Applies to embedded SQL applications, SQL stored procedures Static SQL application depicted

C file(.c)

bind file(.bnd)

package

library.exe

embeddedC program

(.sqc)

Access plans for static SQL are determined at

BIND time


REBIND

db2rbind database_alias -l <logfile>

Example:

db2rbind sample -l mylog.txt


Maintenance Choices• Automated Maintenance

– Have DB2 automatically look after maintenance for you (REORG, RUNSTATS, BACKUP)

• Manual Maintenance– You perform maintenance activities when the need

arises

• Create Scripts to Perform Maintenance– Schedule regular execution of scripts


Automated Maintenance• Based on a user-defined maintenance window

– DB2 will perform maintenance on this window ONLY if needed.

– Two maintenance windows:• ONLINE: For online maintenance activities such as

RUNSTATS and online BACKUP. These can be defined at any time because the database remains fully accessible

• OFFLINE: For offline maintenance activities such as offline BACKUP and REORG. Database may become inaccessible and any connected applications may be affected.

– Database keeps track of operations performed and schedules any needed maintenance in the next appropriate maintenance window


Scheduled Maintenance Using Task Center• More time-consuming than automatic maintenance, but

more customization possibilities– E.g. different tables might have different backup needs

• Task Center is the central location for all scheduled activities for the DB2 administration tools– It is the main interface where all tasks can be created,

edited, and scheduled


Performance

• Configure parameters– Use the Configuration Advisor – The bufferpool is the most important parameter to

configure• This is like cache for databases• Do not over allocate physical memory to the

bufferpool

• Design good indexes – Use the Design Advisor – Indexes can reduce sorts


Performance• Choose the right locking strategy

– Depending on your application logic choose the appropriate isolation level. UR provides the most concurrency.

• Reduce deadlocks by minimizing:– Repeatable Read isolation– Lock Escalation– Lock Conversion– Bad Access plans (table scans)– Catalog Modification– Referential Constraint Enforcement


Performance• Minimize network traffic

– Use stored procedures– Limit the fetch size using clauses like:

• Optimize for X rows: Use this clause to determine the best communications buffer size.

• fetch first x rows only: Limit on the number of rows retrieved

Eg: SELECT EMPNAME, SALARY FROM EMPLOYEE

ORDER BY SALARY DESC

FETCH FIRST 100 ROWS ONLY

OPTIMIZE FOR 20 ROWS


Performance

• Dynamic vs. Static SQL– Static SQL performs better than dynamic SQL– If must use dynamic SQL, ensure to use parameter

markers

• Code your SQL appropriately– Don’t ask for more than you need

• For example, asking for all the columns is not good, like in: Select * from …

– Analyze bad performing SQL with Visual Explain


Visual Explain

Execute & Access Plan

Statement to analyze

Access Plan


Visual Explain