The Top 10 DB2 LUW Mistakes

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Marybeth Townsend
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DB2Night Show The Top 10 DB2 LUW Mistakes P.O. Box 200, 5520 AE Eersel, The Netherlands Tel.:+31.497-530190, E-mail: kbrant@kbce.

date either by a new version of DB2, a new release, a Small Programming Enhancement (SPE) or a Programming Temporary Fix (PTF).

1 DB2Night Show The Top 10 DB2 LUW Mistakes P.O. Box 200, 5520 AE Eersel, The Netherlands Tel.: , Disclaimer and Trademarks Please be aware that the actual programming techniques, algorithms and all parameters used in examples given in this presentation are subject to change at some future date either by a new version of DB2, a new release, a Small Programming Enhancement (SPE) or a Programming Temporary Fix (PTF). The information contained in this presentation is provided for informational purposes only. While efforts were made to verify the completeness and accuracy of the information contained in this presentation, it is provided as is, without warranty of any kind, express or implied. In addition, this information is based on IBM s current product plans, strategy and documentation, which are subject to change by IBM without notice. KBCE shall not be responsible for any damages arising out of the use of, or otherwise related to, this presentation or any other provided documentation. The use of this information or the implementation of any of these techniques is a customer responsibility and depends on the customer s ability to evaluate and integrate them into the customer s operational environment. While each item may have been reviewed for accuracy in a specific situation, there is no guarantee that the same or similar results will be obtained elsewhere. Customers attempting to adapt these techniques to their own environments do so at their own risk. DB2 is a trademark of International Business Machine corporation. This presentation uses many terms that are trademarks. Wherever we are aware of trademarks the name has been spelled in capitals. DB2 Academy 2 1

Mistake #1 Running 32 bits DB2 on 32 bits platform Happens more often on Windows than Linux Many systems need MORE memory NOT more CPU In theory 32 bit can address 4 GB but windows is limited to 3GB

2 Mistake #1 Running 32 bits DB2 on 32 bits platform Happens more often on Windows than Linux Many systems need MORE memory NOT more CPU In theory 32 bit can address 4 GB but windows is limited to 3GB Extra memory is useless! Win32 is greedy, reserves about 1GB for itself Win32 memory is fragmented DLL once loaded is difficult / impossible to move Memory map looks like Swiss cheese Difficult to get single memory chunk bigger than 1.2GB Do not use tricks like /PAE switch Solution not so easy, remember that 32 bit backup CANNOT be restored on 64 bit target DB2 DB2 Academy 3 Mistake #2 Important databases are not activated First connection gets the database going Starts Database Processes Allocates all memory needed (all new pools are empty) Allocates Log Files (and do crash recovery if needed) Depending on size of buffer pools and other areas: 0,3 5 secs If extra work (e.g. crash recovery) much longer Last disconnect flush pools / log, closes all files, shutdown DB New connections wait until shutdown complete Explains "random bad response time" in some cases Solution: ACTIVATE DATABASE command (offline backup needs de-activated database) DB2 Academy 4 2

3 Mistake #3 Still running on default parameters Many default parameters in DB2 are WRONG Examples: LOCKTIMEOUT = -1 in DB CFG Buffer Pools too small Review values and set your own standard Many parameters can be automatic (not automatic by default) See what Configuration Advisor wants to change Do not take every change for granted and not all is fixed Solution: Review db2 registry, dbm & db config and bp settings Fix all incorrect and dangerous values (run config advisor) DB2 Academy 5 Mistake #4 Not tuning DB2 for maximum performance Many DB2 Systems are never properly tuned Memory Allocation (automatic is NOT always best) Expensive Disk Array incorrectly configured Make sure SAN LUN mapping is correctly done Align extend size with stripe size Allow DB2 to use multiple IO Servers Prefetch automatic in DDL DB2_PARALLEL_IO=*:n (n= number of internal disks) And more.. Solution: educate yourself and tune! (it pays back!!) Not doing education to save money is like stopping a watch to save time DB2 Academy 6 3

4 Mistake #4 More on IO!! Monitor your IO configuration! Logical Reads / Physical Reads No over-kill on page sizes! KISS again Separate Index from Data from Large Like it used to be!! Tune your Bufferpools! Trust STMM or tune yourself? Have you considered NUMBLOCKS for pre-fetch? Better less bufferpools than too many Performance is a balance between CPU / Memory / IO Memory is cheap and brings down IO! CPU is in general NOT the problem Solution: more memory and well tuned bufferpools! DB2 Academy 7 Mistake #5 Database server is not a Database server Too much other activity on the server: Try to avoid long running "batch" program on same server Stealing CPU, eating memory and causing non database I/O Other programs don't belong here (e.g. mail server, file server) Carefully review services and daemons running Wrong hardware A file server is NOT a database server Wrong network The connection between apps and db server should be ultra high performance (not part of normal network?) Solution: A multi tier solution (App server DB server / Disk Array) with high performance equipment Run batch in non-prime time! DB2 Academy 8 4

Mistake #6 Too many Instances and Databases What is the reason to start a new database or a new instance? Why do you want less databases? Is this a task for Self Tuning Memory Manager (STMM)?

5 Mistake #6 Too many Instances and Databases What is the reason to start a new database or a new instance? Why do you want less databases? Is this a task for Self Tuning Memory Manager (STMM)? STMM is designed for optimal tuning within database STMM is conservative in allocating memory Has to be decreasing a BP is very time consuming STMM adjustment is always an after fact Can you tune without STMM? How much precious memory is lost? How unfair is the battle for resources? Solution: KISS! Keep It Simple System ;-) DB2 Academy 9 Mistake #7 Table(space) spaghetti (RI - schema) How to design your physical layout? Two big reason for split: performance and recovery Performance: Location, DDL parameters and # tables influence performance Recovery Data can be restore restored on database and tablespace level Keep in mind that restore is NOT done on table level!! If conflict in schema or Referential Integrity (RI) then much more difficult scenario (redirected restore, unload etc.) Solution: carefully (re)think your table : tablespace mapping DB2 Academy 10 5

6 Mistake #8 Abnormal shutdown of DB2 Shutdown (re-boot) server DB2 does not do normal DB2 shutdown Operating system ask DB2 for shutdown DB2 will start shutdown like DB2STOP FORCE OS quickly looses patience and KILLS DB2 processes Result: DB2 needs crash recovery during start-up DO not monkey around with DB2 daemons / services If you have done so REBOOT! Do a NORMAL shutdown when applying a fixpack or migrating Solution: Have proper shutdown procedures DB2 Academy 11 Mistake #9 NOT looking after DB2 DB2 needs maintenance runstats / backup / reorg Leave to automatic maintenance or do it yourself? Runstats & Reorg also do activity outside assigned window But wait there is more! DB2DIAG / Prune history / Archive logs DB2DIAG is VERY important, look at it daily! mail s "db2 diag log" info@kbce.com < DB2DIAG H 1d DB2DIAG A \diag_archive Solution: create procedures, use them and document them DB2 Academy 12 6

7 DB2DIAG: even warning can be useful! E21368H971 LEVEL: Warning PID : 4676 TID : 2848 PROC : db2syscs.exe INSTANCE: DB2 NODE : 000 DB : TOOLSDB APPHDL : APPID: *LOCAL.DB AUTHID : ADMINISTRATOR EDUID : 2848 EDUNAME: db2agent (DBP1SDA) 0 FUNCTION: DB2 UDB, Self tuning memory manager, stmmcalcautoscalefactor, probe:10 0 MESSAGE : Current DB configuration exceeds free INSTANCE_MEMORY. Self-tuning memory manager resetting automatic memory consumers to default values. DB2 Academy 13 Mistake #10 Who did what, why and when? Monday morning 8:05 telephone rings "You need to come, CPU is 100% and response time is bad!!" What happened?... "WE DON T KNOW!!!" No performance data from before No "rollback" scenario No tools to quickly detect shift in performance So happy hunting! Start performance tools on a 100% busy machine Solution: Have performance baseline (CPU, IO) by program. Have tools to quickly detect which SQL statements eat the CPU alive. DB2 Academy 14 7

Is your system OK? 1. Running 32 bits DB2 on 32 bits platform 2. DB2 Databases not activated 3. Still running by default parameters 4. Not tuning the system for maximum performance 5.

8 Is your system OK? 1. Running 32 bits DB2 on 32 bits platform 2. DB2 Databases not activated 3. Still running by default parameters 4. Not tuning the system for maximum performance 5. Database server is not a database server 6. Too many Instances and Databases 7. Tablespace mess 8. Abnormal shutdown of DB2 9. Not looking after DB2 10.Who did what, why and when? DB2 Academy 15 Questions? MEI DB2 Academy 16 8

What Developers must know about DB2 for z/os indexes

CRISTIAN MOLARO CRISTIAN@MOLARO.BE What Developers must know about DB2 for z/os indexes Mardi 22 novembre 2016 Tour Europlaza, Paris-La Défense What Developers must know about DB2 for z/os indexes Introduction