Db2 may experience a hang shortly after an object is created and
committed while an agent is trying to allocate new extents for
the new object.
While allocating extents for this object, the agent will check
if the object state includes SQLB_OBJ_CreateInProg.
If this state is set, and the object creation has already been
committed, the agent will attempt to clear the
SQLB_OBJ_CreateInProg state.
Doing so requires refreshing the TCB which may require a TCB
load depending on if the TCB has previously been loaded into
memory or not.
If this agent has other pages fixed prior to trying to load the
TCB, this agent may become involved in a circular wait with
other agents.
The agent allocating extents to the object will have a stack
similar to the following:
getConflictComplex
getConflict
sqlo_latch_ns
sqldLoadTCBObjDesc
sqldFixTCBObj
sqldRefreshObj
sqlbFixAndSearchOneSMPPage
sqlbSearchSomeSMPs
sqlbAllocateExtent
sqlbDMScheckObjAlloc
sqlbExtendObject
sqliGetPages
sqliSearchMapsAndGetPage
sqliGetPageBufferPool
sqlischa
sqlischa
sqliaddkP8sqeAgent
sqldKeyInsert
sqldRowInsert
This agent will be holding page latches and waiting on the TCB
load latch:
Waiting on latch type: (SQLO_LT_SQLD_TCB__loadInProgress) -
Address: (0x7ff0639344a0), Line: 9511, File: sqldtcb.C
Holding Latch type: (SQLO_LT_SQLI_INX_PAGE_CACHE__ipcLatch) -
Address: (0x7ff0639346b8), Line: 1108, File: sqligtpg.C
HoldCount: 1
Holding Latch type:
(SQLO_LT_SQLB_POOL_ADDRESS_INFO__pool_address_latch) - Address:
(0x7ff03c096fe0), Line: 176, File: sqlegss.h HoldCount: 1
Holding Latch type: (SQLO_LT_SQLB_POOL_CB__readLotch) - Address:
(0x7fd4b40d6d40), Line: 2577, File: sqlbSMP.C HoldCount: 1
Holding Latch type: (SQLO_LT_SQLP_SAVEPOINTS__spLatch) -
Address: (0x7ff055e0ed38), Line: 72, File: sqlpSavepoint.h
HoldCount: 1
Holding Latch type: (SQLO_LT_SQLB_POOL_CB__ptfLotch) - Address:
(0x7fd4af551fa0), Line: 2577, File: sqlbSMP.C HoldCount: 1
Holding Latch type: (SQLO_LT_sqeSuspendIOCB__m_suspendIOCBLatch)
- Address: (0x20d5cef00), Line: 2570, File: sqlbSMP.C HoldCount:
1
Holding latch type: (SQLO_LT_SQLB_BPD__bpdLatch_SX) - Address:
(0x7ff02950d788), mode: S, Line: 1099, File: sqlbslat.h
Holding latch type: (SQLO_LT_SQLB_BPD__bpdLatch_SX) - Address:
(0x7ff029527448), mode: X, Line: 1099, File: sqlbslat.h
Holding latch type: (SQLO_LT_SQLB_BPD__bpdLatch_SX) - Address:
(0x7ff02950d888), mode: X, Line: 1099, File: sqlbslat.h
Holding latch type: (SQLO_LT_SQLB_BPD__bpdLatch_SX) - Address:
(0x7ff0294f5ac8), mode: X, Line: 2223, File: sqlbgbc.C
Holding latch type: (SQLO_LT_SQLB_BPD__bpdLatch_SX) - Address:
(0x7ff0294eda88), mode: X, Line: 2223, File: sqlbgbc.C
The rest of this example shows how two other agents may be
holding page latches and a TCB load latch such that a circular
wait occurs. These specific stacks are not necessarily required
for this problem to occur but are one such example that will
cause a circular wait. This agent is holding the TCB load latch
that the aforementioned agent is waiting on:
getConflictComplex
getConflict
sqloSXULatch::get
sqlbUpgradePageLatchForRefreshAndPLock
sqlbgbGetPagePLock
sqlbfix
sqliRefreshInfoPage
sqldRefreshIndexChain
sqldFixTCBP
sqldLockTableFixTCB
sqldGetInsertTable
sqldBuildForADC
sqldAttemptADC
sqldRowInsert
Waiting on latch type: (SQLO_LT_SQLB_BPD__bpdLatch_SX) -
Address: (0x7ff0294edc88), Line: 3660, File: sqlbslat.h
Holding Latch type: (SQLO_LT_SQLD_TCB__loadInProgress) -
Address: (0x7ff0639344a0), Line: 607, File: sqldtm_inlines.h
HoldCount: 1
Holding Latch type: (SQLO_LT_SQLP_SAVEPOINTS__spLatch) -
Address: (0x7ff0469fdd38), Line: 72, File: sqlpSavepoint.h
HoldCount: 1
Holding Latch type: (SQLO_LT_SQLD_TCB_LOTCH__tcbValidityLotch) -
Address: (0x7ff065d6d360), Line: 11192, File: sqldtcb.C
HoldCount: 1
Holding Latch type:
(SQLO_LT_SQLD_TCB_LOTCH__tcbIndexValidityLotch) - Address:
(0x7ff063934540), Line: 10934, File: sqldtcb.C HoldCount: 1
Finally, the above agent is waiting on a page latch held by the
following agent, which itself is waiting on a page latch held by
the first agent that is waiting on the TCB load latch, and
completing the circular wait:
getConflictComplex
getConflict
sqlbfix
sqlifix
sqliFixPageWithChildPtr
sqlischa
sqlischa
sqliaddk
sqldKeyInsert
sqldRowInsert
Waiting on latch type: (SQLO_LT_SQLB_BPD__bpdLatch_SX) -
Address: (0x7ff029527448), Line: 511, File: sqlbslat.h
Holding Latch type: (SQLO_LT_SQLP_SAVEPOINTS__spLatch) -
Address: (0x7ff055054d38), Line: 72, File: sqlpSavepoint.h
HoldCount: 1
Holding latch type: (SQLO_LT_SQLB_BPD__bpdLatch_SX) - Address:
(0x7ff0294edc88), mode: S, Line: 1099, File: sqlbslat.h |
