IN-MEMORY population and auto I/O slot resize

In my last blog post on IN-MEMORY when investigating the amount of work done on behalf of  IN-MEMORY population/[trickle] re-population i have done some observation concerning auto I/O slot resize.So here is more detail in a very short post(Sadly no time for a deeper investigation 😦 ).

In this test we will be comparing direct path read done on a big table : one by the in-memory slave process in the context of in-memory population vs direct path read issued by user action reading the table.


  • Test database (Linux)
  • BIG_TABLE size 2GB
  • Using event 10365 to turn on debug information for adaptive direct reads
  • Using systemtap script to check for I/O slot usage and re-sizing

Reading a table using direct path read :

select count(*) from big_table2

Extract of 10365 trace event :

Capture trace events

Extract of systemtap script:

Capture sans inmemory stap

Observation :

Adaptive direct path read is using only the default two I/O slot at a time for reading the hole table.There is no resize at this time.(for more info on how to control I/O slot resize check this )

INMEMORY population  using direct path read (w0nn process):

Extract of 10365 trace event :

Capture inmemory trace

Extract of systemtap script:

Capture stap inmemory

Observation :

The output of the 10365 trace event seem wrong ! Although it report that the number of I/O slot used by the session is 2 the systemtap script show that more slot are used. Also this time more I/O slot are used at the beginning compared to the previous case witch used the default value of 2 I/O slot to begin with.

That’s it 😀

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