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2843506 - 100% CPU usage on Time Stamp Counter (TSC)

Symptom

  • The HANA System's CPU utilization is exhausted on at least one host or more.
  • Even after a full restart of the DB , another massive CPU load and/or blocked transactions are observed on the system.
  • From the kernel profiler trace  (1804811 - SAP HANA Database: Kernel Profiler Trace), one particular callstack module is observed:

 

        The main single CPU consumer is: vgettimeofday

      Node Legend:
      <funcName>
      I: <function and descendant CPU time>
      E: function only time
     (Sys: I: <function and descendant time>, E: function only time)

kernel node.jpg


   So in this example, the CPU is consumed by 22% alone for timestamp calls. This is not normal behavior.

   The indexserver trace also shows us that we have a system timer fallback:

   2019-08-19 13:28:24.081575 w Basis Timer.cpp(00718) : Fallback to system call for HR timer


 

  • A high frequency of SQLExecutor threads with this callstack is observed in the indexserver runtime dumps :
       [thr=99546]: SqlExecutor at
       1: 0xffffffffff60017b in [vgettimeofday]+0x177 (<unknown>)

 

  • A check of the clocksource from OS layer on the Linux host reveals it is not set at 'tsc'
    ~]# cat /sys/devices/system/clocksource/clocksource0/current_clocksource

 

Image/data in this KBA is from SAP internal systems, sample data, or demo systems. Any resemblance to real data is purely coincidental.


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Environment

  • SAP HANA Database Platform Edition 1.0 
  • SAP HANA Database Platform Edition 2.0
  • Intel CPUs 

Product

SAP HANA 1.0, platform edition ; SAP HANA, platform edition 2.0

Keywords

vgettimeofday, High CPU, tsc, clocksource , KBA , HAN-DB-PERF , SAP HANA Database Performance , Problem

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