A performance degradation in Db2 V11.1 M4FP4 can be observed
when joining VARCHAR columns in BLU queries on AIX.
Compared Db2 V11.1 M4FP4 to Db2 V11.1 M3FP3, the degradation
reduced query performance up to 20-30%.
If you analysis such queries using tprof, you can find
ibm_cde::services::ManagedStringBase::assign very close to the
top.
A sample tprof output of a query affected by this issue:
...
Total Ticks For All Processes
(/db2/m3_1109/lib64/libdb2blu.a[shr_64.o]) = 18097
Subroutine Ticks % Source
Address Bytes
========== ===== ====== ======
======= =====
.ibm_cde::query::ConcatEvaluator::computeListOfNotCodeableInputs
(bool&,ibm_cde::types::BitString&,ibm_cde::query::WorkUnit&)
2561 9.82 ConcatEvaluator.cpp 4c80848 3520
.ibm_cde::services::ManagedStringBase::assign(const unsigned
char*,const unsigned long) 1791 6.87
ColumnDictionaryVersionBase.cpp 1125638 200
.ibm_cde::types::VarLenString::initCompareFunc() 941 3.61
VarLenString.cpp bbceb8 2b0
.ibm_cde::types::VarLenString::formString(const
char*,ibm_cde::types::DataType,unsigned short) 923 3.54
ColumnDictionaryVersionBase.cpp 110a4a8 2d0
.ibm_cde::data::ColumnDictionaryVersion::decode(ibm_cde::data::QCode,ibm_cde::types::ValUncoded&)
const 895 3.43 ColumnDictionaryVersionBase.cpp 1168908
360
... |
