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2762492 - Writer Node not responding, stack has 'hos_dualmutex::LockAndPromote', 's_VersioningBlockmap::LockRFRB' ,... etc -- SAP IQ

Symptom

Under rare circumstances, the server may become unresponsive in an MPX environment under aggressive DML operation. Stacktraces taken minutes apart will be identical and will indicate that three separate threads are blocked inside functions: hos_dualmutex::LockAndPromote, s_VersioningBlockmap::LockRFRB, s_bufman::FindBlockMap1. This has been fixed.

In particular,
 
- One thread is holding the _blockmapsHTMutex (inside s_blockmap::Unlock) while trying to get the blockmap _Mutex;
  - A second thread is holding the blockmap _Mutex (inside s_blockmap::RegisterPhysicalBlockId) while trying to get the rollback lock; and
  - A third thread is holding the rollback lock (inside s_VersioningBlockmap::Allocate) while trying to get the _blockmapsHTMutex,
hence, the deadlock.


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Environment

SAP IQ 16

Keywords

deadlock, hang, unresponsive, 814876, CR#814876, , KBA , BC-SYB-IQ , Sybase IQ , Problem

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