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.

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
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9. DB2DART – Formatting data
Example: db2dart <db> /DD /TSI 2 /OI 6
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10. DB2DART – Repairing data
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11. DB2DART – My 3 Key DB2DARTs
DARTs
1. Storage Reclamation and High Water Mark
2. Index Corruption
3. Extracting Data
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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
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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
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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
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23. db2dart /DHWM – Drop table ID 5
LIST TABLESPACES SHOW DETAIL
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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
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26. db2dart /LHWM – after REORG
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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
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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