IZ20211: INSTANCE TRAP/PANIC IF SORT TRIES TO UNFIX A TEMP-PAGE THAT HAS ALREADY BEEN UNFIXED, DEFENSIVE CODE TO PREVENT PANIC.

DB2 Version 9.5 Fix Pack 3b for Linux, UNIX, and Windows
DB2 Version 9.5 Fix Pack 4  for Linux, UNIX, and Windows
DB2 Version 9.5 Fix Pack 3a for Linux, UNIX, and Windows
DB2 Version 9.5 Fix Pack 3 for Linux, UNIX, and Windows
DB2 Version 9.5 Fix Pack 4a for Linux, UNIX, and Windows
DB2 Version 9.5 Fix Pack 5 for Linux, UNIX, and Windows
DB2 Version 9.5 Fix Pack 6a for Linux, UNIX, and Windows
DB2 Version 9.5 Fix Pack 7 for Linux, UNIX, and Windows
DB2 Version 9.5 Fix Pack 8 for Linux, UNIX, and Windows
DB2 Version 9.5 Fix Pack 9 for Linux, UNIX, and Windows
DB2 Version 9.5 Fix Pack 10 for Linux, UNIX, and Windows

APAR status

• Closed as program error.

Error description

• The Instance will trap/panic due to an as-yet-unknown problem
  where the Sort facility, during the merge phase, attempts to
  unfix a bufferpool page (belonging to a temporary table) that
  has already been unfixed.
  The problem is very rare, and the root cause is still unknown.
  
  This APAR will add defensive code that checks if the page is
  already unfixed before unfixing it, and if so, it will force the
  application using the Sort to fail with a -901, instead of
  causing the instance to panic/trap.
  
  A stack trace containing functions sqlbufix and sqlsmerg is
  common what this problem occurs:
  
  __1cTsqlbLatchPinnedPage6FpnLSQdDLB_FIX_CB__i_(0xffffffff7e7b8f8
  8,0x4da650760,0x10000,0x397c,0xffff7c00,0xffff7fff) + 0x338
  __1cIsqlbufix6FpnLSQdDLB_FIX_CB_cc_i_(0x4,0x4da650760,0x0,0x2,0x
  242299ec0,0x2) + 0x180
   __1cMsqlsmergerec6FpnUsqle_agent_privatecb_pnKSQdDLS_SLDES_pnKS
  QdDLS_MBUFS_L_i_(0xffffffff7331b040,0x604f1efa0,0x2,0xffffffff73
  210080,0x20100020,0xffffffff7efbc920) + 0x608
  __1cIsqlsfetc6FpnUsqle_agent_privatecb_pnISQdDLD_CCB_ipnKSQdDLD_
  DPRED_ppnKSQdDLD_VALUE_pnISQdDLZ_RID_pc_i_(0xffffffff7331b040,0x
  0,0x1,0xffffffff7183be88,0x1d,0xffffffffffffffff) + 0xbbc
  __1cUsqlriFetchSortedTemp6FpnIsqlrr_cb_pnJsqlri_tao_l_i_(0xfffff
  fff73310ea0,0xffffffff7183bce8,0x3,0xffffffff7183bce8,0x10000,0x
  80) + 0x30
  __1cKsqlriFetch6FpnIsqlrr_cb_pnJsqlri_tao_l_i_(0xffffffff73310ea
  0,0xffffffff7183bce8,0x3,0x7f7b8,0x0,0x1) + 0x5c
  __1cHsqlrita6FpnIsqlrr_cb__i_(0x0,0xffffffff73310ea0,0x0,0xfffff
  fff7183bce8,0xffffffff7efbc888,0x1578) + 0x6cc
  __1cPsqlriSectInvoke6FpnIsqlrr_cb_pnMsqlri_opparm__i_(0xffffffff
  73310ea0,0xffffffff7cf42f58,0x1578,0xffffffff7183c228,0xffffffff
  7331b040,0x0) + 0x29c
  ...snip...
  

Local fix

Problem summary

• ERROR DESCRIPTION:
  The Instance will trap/panic due to an as-yet-unknown problem
  where the Sort facility, during the merge phase, attempts to
  unfix a bufferpool page (belonging to a temporary table) that
  has already been unfixed.
  The problem is very rare, and the root cause is still unknown.
  
  This APAR will add defensive code that checks if the page is
  already unfixed before unfixing it, and if so, it will force the
  application using the Sort to fail with a -901, instead of
  causing the instance to panic/trap.
  
  A stack trace containing functions sqlbufix and sqlsmerg is
  common what this problem occurs:
  
  __1cTsqlbLatchPinnedPage6FpnLSQdDLB_FIX_CB__i_(0xffffffff7e7b8f8
  8,0x4da650760,0x10000,0x397c,0xffff7c00,0xffff7fff) + 0x338
  __1cIsqlbufix6FpnLSQdDLB_FIX_CB_cc_i_(0x4,0x4da650760,0x0,0x2,0x
  242299ec0,0x2) + 0x180
   __1cMsqlsmergerec6FpnUsqle_agent_privatecb_pnKSQdDLS_SLDES_pnKS
  QdDLS_MBUFS_L_i_(0xffffffff7331b040,0x604f1efa0,0x2,0xffffffff73
  210080,0x20100020,0xffffffff7efbc920) + 0x608
  __1cIsqlsfetc6FpnUsqle_agent_privatecb_pnISQdDLD_CCB_ipnKSQdDLD
  DPRED_ppnKSQdDLD_VALUE_pnISQdDLZ_RID_pc_i_(0xffffffff7331b040,0x
  0,0x1,0xffffffff7183be88,0x1d,0xffffffffffffffff) + 0xbbc
  __1cUsqlriFetchSortedTemp6FpnIsqlrr_cb_pnJsqlri_tao_l_i_(0xfffff
  fff73310ea0,0xffffffff7183bce8,0x3,0xffffffff7183bce8,0x10000,0x
  80) + 0x30
  __1cKsqlriFetch6FpnIsqlrr_cb_pnJsqlri_tao_l_i_(0xffffffff73310ea
  0,0xffffffff7183bce8,0x3,0x7f7b8,0x0,0x1) + 0x5c
  __1cHsqlrita6FpnIsqlrr_cb__i_(0x0,0xffffffff73310ea0,0x0,0xfffff
  fff7183bce8,0xffffffff7efbc888,0x1578) + 0x6cc
  __1cPsqlriSectInvoke6FpnIsqlrr_cb_pnMsqlri_opparm__i_(0xffffffff
  73310ea0,0xffffffff7cf42f58,0x1578,0xffffffff7183c228,0xffffffff
  7331b040,0x0) + 0x29c
  ...snip...
  

Problem conclusion

• First fixed in DB2 UDB Version 9.1 FixPak 6 and  9.5, FixPak 3.
  

Temporary fix

Comments

APAR Information

• APAR is sysrouted FROM one or more of the following:

  IZ20209

• APAR is sysrouted TO one or more of the following:

Modules/Macros

• engn_sqs
  

Fix information

• Fixed component name

  DB2 UDB ESE SOL

• Fixed component ID

  5765F4102

Applicable component levels

• R950 PSY

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