DB2DART - DB2Night Show October 2011
1 like2,519 views
DB2DART is a tool that allows DBAs to inspect, format, and repair DB2 databases and objects. It can be used to handle storage reclamation issues by lowering high water marks, detect and repair index corruption, extract data from corrupt tables, and remove backup pending states. DB2DART provides granular analysis at the database, tablespace, and table level and its repair capabilities save DBAs from having to call support or restore from backups in many cases.
DB2DART - DB2Night Show October 2011
- 1. DB2DART DART Iqbal Goralwalla DB2Night Show October 14, 2011 The Information Management Specialists
- 2. About Triton • Formed in 1996 • IBM Premier Business Partner • Largest independent DB2 Consultancy in the UK • Strong team of highly experienced and certified DB2 specialists • Work with customers across a range of sectors providing them with DB2 consultancy and support for both DB2 LUW and DB2 z/OS • Preferred DB2 services supplier to IBM UK and others The Information Management Specialists
- 3. About Me • Head of Midrange (DB2 on LUW) at Triton Consulting • Principal Consultant on DB2 LUW • Experience of DB2 LUW since DB2 Common Server • IBM Champion for Data Management • Tendency to talk too much The Information Management Specialists
- 4. DB2DART • DB2DART – An Overview • My 3 Key DB2DARTs • My bonus DB2DART • Anything on DB2DART and DPF? • What about INSPECT? • GOTCHAS The Information Management Specialists
- 5. DB2DART – An Overview db2top • One of the less used db2pd performance reporting db2exfmt tools db2diag • Historically used with db2support IBM support db2trc • DBAs can use the tool – db2dart increases productivity Why am I here? The Information Management Specialists
- 6. DB2DART – An Overview • Database Analysis and Reporting Tool • “Offline” tool for checking the architectural correctness of a database Checks validity of meta-data structures, page headers, row headers, etc. • Critical for investigating problems involving data corruption • Runs against the data on disk Not aware of what’s in the buffer pool May show false errors if users are connected to the database The Information Management Specialists
- 7. DB2DART – An Overview • Granularity Database: db2dart <db> /DB Tablespace: db2dart <db> /TS Table: db2dart <db> /T /TSI /OI • Options for inspecting, formatting, and repairing data • Run db2dart /H to see all of the supported options The Information Management Specialists
- 8. DB2DART – Inspecting data Examples: db2dart <db> /DB db2dart <db> /TS /TSI 2 db2dart <db> /T /TSI 2 /OI 6 The Information Management Specialists
- 9. DB2DART – Formatting data Example: db2dart <db> /DD /TSI 2 /OI 6 The Information Management Specialists
- 10. DB2DART – Repairing data The Information Management Specialists
- 11. DB2DART – My 3 Key DB2DARTs DARTs 1. Storage Reclamation and High Water Mark 2. Index Corruption 3. Extracting Data The Information Management Specialists
- 12. Storage Reclamation – the DBA dilemma Why is the space not being Deleted thousands of released? rows Dropped a BIG table Reorged the table The Information Management Specialists
- 13. Storage Reclamation – HWM for DMS tablespaces • High Water Mark (HWM) is the highest numbered page that is currently allocated in a DMS tablespace • HWM can be much higher than the number of pages currently in use due to: Dropped tables or delete activity Offline table reorg using same tablespace Index reorg using “allow read or write access” • Makes it difficult to release unused disk space for reuse • HWM can be seen using LIST TABLESPACES SHOW DETAIL or GET SNAPSHOT FOR TABLESPACES The Information Management Specialists
- 14. Storage Reclamation – HWM for DMS tablespaces • LIST TABLESPACES SHOW DETAIL The Information Management Specialists
- 15. HWM – Dropped table (1) DMS TABLESPACE DMS TABLESPACE T1 T1 5 pages 5 pages Drop table T2 T2 Free 3 pages 3 pages T1 T1 2 pages 2 pages Table Space HWM Used pages = 10 Used pages = 8 does NOT change HWM = 10 HWM = 10 The Information Management Specialists
- 16. HWM – Dropped table (2) DMS TABLESPACE DMS TABLESPACE T1 Free 5 pages 5 pages Drop table T1 T2 T2 3 pages 3 pages T1 Free 2 pages 2 pages Table Space HWM Used pages = 10 Used pages = 3 DOES change HWM = 10 HWM = 8 The Information Management Specialists
- 17. HWM – Offline Table Reorg (1) REORG TABLE T1 DMS TABLESPACE INTERMEDIATE STATE DMS TABLESPACE T1 T1 Free 5 pages 7 pages T1 Free T1 4 pages Shadow 6 pages Copy Used pages = 5 Used pages = 4 HWM = 5 Table Space HWM HWM = 11 INCREASES The Information Management Specialists
- 18. HWM – Offline Table Reorg (2) REORG TABLE T1 DMS TABLESPACE INTERMEDIATE STATE DMS TABLESPACE T1 Free Shadow T1 7 pages Copy 4 pages Free T1 T1 7 pages 4 pages Used pages = 4 Used pages = 4 HWM = 11 Table Space HWM HWM = 4 DECREASES The Information Management Specialists
- 19. HWM headaches • Space not released even though free extents available • Redirected RESTORE needs space equal to or greater than the HWM All extents in DMS table spaces up to the HWM copied to the backup image. Tablespaces containers cannot be reduced below HWM • ALTER TABLESPACE <drop container/reduce containers size> only affects extents above the HWM The Information Management Specialists
- 20. Storage Reclamation – the DBA dilemma (DB2 9.1/9.5) Shall I call IBM DB2DART Support? Not when I’m around! The Information Management Specialists
- 21. Storage Reclamation – DB2DART 1 DART • db2dart /DHWM – display table space and high- water mark information A map of the extents in the table space, showing objects owning them The ID and type of the object holding the high-water mark extent Amount of free extents and in-use extents below the high-water mark TIP: If online, use db2pdcfg –flushbp first (V9.1FP5, V9.5FP1) The Information Management Specialists
- 22. db2dart /DHWM LIST TABLESPACES SHOW DETAIL The Information Management Specialists
- 23. db2dart /DHWM – Drop table ID 5 LIST TABLESPACES SHOW DETAIL The Information Management Specialists
- 24. Storage Reclamation – DB2DART • db2dart /LHWM – Assists in lowering the high-water mark Table space ID and desired high-water mark are required May not be possible to actually lower it to the desired level Use "0" for the desired high-water mark to go as low as possible Result is a list of operations to execute (EXPORT/LOAD, REORG, etc.) Estimate of resulting in use and free extents below the high-water mark is displayed for each step The Information Management Specialists
- 25. db2dart /LHWM The Information Management Specialists
- 26. db2dart /LHWM – after REORG The Information Management Specialists
- 27. Storage Reclamation – DB2DART • db2dart /RHWM – Removes empty SMP extents holding up the high-water mark DB2 9.5 – ALTER TABLESPACE <tbsp> REDUCE/DROP ► Drops/reduces containers to the table space’s high- water mark ► First removes empty SMP extents ► No need for db2dart /RHWM The Information Management Specialists
- 28. Storage Reclamation – DB2DART enhancements • V9.1 FP4 – db2dart /DHWM and /LHWM can be run against active/inconsistent database IZ04647 http://www- 01.ibm.com/support/docview.wss?uid=swg1IZ04647 • V9.1 FP5 – db2dart /DHWM is not correct when an empty SMP extent is holding the HWM IZ07663 http://www- 01.ibm.com/support/docview.wss?uid=swg1IZ07663 The Information Management Specialists
- 29. Storage Reclamation – DB2 9.7 • For a DMS or Automatic Storage table space created in DB2 9.7, you can use reclaimable storage to return unused storage to the system for reuse. • For Automatic Storage table spaces, the REDUCE MAX option of ALTER TABLESPACE can be used to release all unused spaced • For DMS, two steps are required to release the unused extents The High Water can be reduced to match the number of used extents with the LOWER HIGH WATER MARK option The REDUCE, RESIZE or DROP options then be used • Reclaiming storage is an online operation The Information Management Specialists
- 30. Index Corruption • Possible causes Hardware or software failure Killing an executing process (e.g., LOAD) After migration from one system to another • Symptoms Bad page errors SQL0980C during a backup database command SQL0902C – database marked bad The Information Management Specialists
- 31. Index Corruption – the DBA dilemma Restore from backup? Shall I call IBM Support? DB2DART Not when I’m around! The Information Management Specialists
- 32. Index Corruption – DB2DART 2 DART • Find out which indexes are problematic db2dart <db> /DD /TSI <pool id> /OI <object id> db2dart <db> /DI /TSI <pool id> /OI <object id> • Mark indexes as invalid db2dart <db> /MI /TSI <pool id> /OI <object id> • Indexes recreated based on INDEXREC (database configuration parameter) ► RESTART ► ACCCESS ► Monitor using db2diag.log The Information Management Specialists
- 33. Index Corruption – DB2DART • Indexes recreated: First access of invalid index RESTART DATABASE LOAD – Build phase Classic offline table reorg • To prevent access to problematic index LOCK TABLE IN EXCLUSIVE MODE The Information Management Specialists
- 34. Index Corruption – DB2DART – Partitioned tables/indexes • db2dart /MI requires table space ID and index object ID. For partitioned indexes, use INDPARTITIONOBJECTID and INDPARTITIONTBSPACEID from SYSCAT.INDEXPARTITIONS. The Information Management Specialists
- 35. Extracting Data • Table space or database is corrupt or inaccessible • Access to “bad/damaged” data causes an instance crash • Need to salvage data Cannot use SQL to select data Cannot use Export Restore from backup image ► Does one exist? ► Circular logging? The Information Management Specialists
- 36. Extracting Data – the DBA dilemma Shall I call IBM DB2DART Support? Not when I’m around! The Information Management Specialists
- 37. Extracting Data – DB2 DART 3 • db2dart <db> /DDEL • Dumped in delimited ASCII format • Prompted for table name (or ID), table space ID, starting page, number of pages, and output file name • LONG VARCHAR or LOB data will not be dumped The Information Management Specialists
- 38. Extracting Data – DB2DART • May require multiple invocations Dump up to “bad/damaged” page using /DDEL option ► Aborts on reaching corruption Dump “bad/damaged” page using /DD option ► Incorrupt data can be viewed Dump rest of pages after “bad/damaged” page using /DDEL option and appropriate start page • Some data loss inevitable The Information Management Specialists
- 39. Backup Pending State (aka “Forced backup”) • LOAD with COPY NO (default) • Logging strategy changed (circular to archival) • LOGARCHIVE enabled • LOGFILSIZ changed while using raw device for logging The Information Management Specialists
- 40. Backup Pending State – the DBA dilemma Do I really need DB2DART to do a backup? Not when I’m around! The Information Management Specialists
- 41. Backup Pending State – bonus DB2DART DART • db2dart <db> /CHST /WHAT DBBP OFF The Information Management Specialists
- 42. DB2DART – Does it work with DPF? • Yes! • Run db2dart on desired partition or on all partitions • Use db2_all to run db2dart on all partitions in a single invocation • Default destination of report file is in diagnostic directory The Information Management Specialists
- 43. DB2DART – IBM service options • /ETS – extends the table limit in a 4 KB table space (DMS only), if possible • /MT – marks table with drop-pending state Needs password – supplied by IBM • /IP – initializes the data page of a table as empty Needs password – supplied by IBM The Information Management Specialists
- 44. What about INSPECT? • Online “equivalent” of DB2DART • Integrated into runtime engine resulting in performance gains Makes use of prefetchers and buffer pools • Runs on all logical nodes in a partitioned system Can be directed to run on specific nodes • Can estimate row compression results for table, dictionary based on sample The Information Management Specialists
- 45. What about INSPECT? • Granular: inspection can be on database, tablespace, or a table • Results (unformatted) are written to the specified file (placed in diagnostic directory path). Use db2inspf to format results The Information Management Specialists
- 46. DB2DART vs. INSPECT • INSPECT does not provide any of the formatting or repair options that db2dart provides • Unlike DB2DART, INSPECT of a tablespace will only process objects that reside in that tablespace. It will not inspect: Corresponding index objects residing in a different tablespace LOB objects residing in a different tablespace Note: running DB2DART on an INDEX tablespace would not seek out the parent data The Information Management Specialists
- 47. DB2DART – Gotchas • Security – user with authority to run the db2dart tool or with access to the db2dart output can gain access to information that they might not be authorized for • LOAD – ALLOW READ ACCESS option not supported if indexes marked invalid The Information Management Specialists
- 48. Summary & Conclusions • DB2DART is a very powerful tool • Can be used by DBAs to deal with: Storage Reclamation Index Corruption Extracting Data Database backup pending state • Increases productivity The Information Management Specialists