Memory bandwidth vs latency response curve

Memory bound applications are sensitive to memory latency and bandwidth that’s why it’s important to measure and monitor them.Even if this two concepts are often described  independently they are inherently interrelated.

According to Bruce Jacob in ” The memory system: you can’t avoid it, you can’t ignore it, you can’t fake it” the bandwidth vs latency response curve for a system has three regions.

  • Constant region: The latency response is fairly constant for the first 40% of the sustained bandwidth.
  • Linear region:  In between 40% to 80% of the sustained bandwidth, the latency response increases almost linearly with the bandwidth demand of the system due to contention overhead by numerous memory requests.
  • Exponential region:  Between 80% to 100% of the sustained bandwidth,  the memory latency is dominated by the contention latency which can be as much as twice the idle latency or more.
  • Maximum sustained bandwidth :  Is 65% to 75% of the theoretical maximum bandwidth.
 Armed with Intel Memory Latency Checker (MLC) let’s check our current system !

Continue reading

Geeky PL/SQL tracer/profiler : Another step

This is my second post under the theme of how to extend our capabilities to trace and profile PL/SQL code.This time motivated by a comment from Luca Canali on my previous post  :

So based on my previous work on geeky PL/SQL tracer let’s see how we can obtain a geeky PL/SQL on-CPU Flame Graph !

Continue reading

Geeky PL/SQL tracer/profiler : First step

This blog post is about how to extend our capabilities to trace and profile PL/SQL code.It’s primarily motivated by few tweets from Franck Pachot and of course because it’s FUN !

Capture 02

Capture 01

So in the first part of this series we are going to answer to this questions : Can we map those underling function to the source PL/SQL object and line number ? Can we obtain a full trace ? Of course yes otherwise there will be no blog post :p

Continue reading

Getting Latch holder info out of the state objects in SGA memory

Updated 12/05/2017

It will be great to have a tool that will extract latch holder information directly from state objects  stored inside the SGA. This way we will reduce the overhead when troubleshooting latch contention an beside that it’s also cool !!

This may sound difficult ! How to proceed ? and the answer is …. Memory reference tracing !

Continue reading

Adaptive Dynamic Sampling : DYNAMIC_SAMPLING_RESULT & STALE_PERCENT

Since oracle 12.2.0.1 Adaptive Dynamic Sampling  result are stored inside SPD as a special directive type “DYNAMIC_SAMPLING_RESULT”. This will allow the result of ADS to be persisted on disk,thus it will survive memory flush and database restart.For more detailed info please check Mauro Pagano blog Post Something new about SQL Plan Directives and 12.2

We may ask at this moment is there some sanity check that will trigger the refresh of this ADS result stored as sql plan directive when the table data is marked stale (STALE_PERCENT) ?

Continue reading