When is the MessageContext released?

  I run a query like "select * from t" and set the break like this:

break exec_simple_query

break MemoryContextDelete

  commands

   p context->name

   c

  end

I can see most of the MemoryContext is relased, but never MessageContext,  when will it be released?

I'm hacking the code with the latest commit.  https://github.com/postgres/postgres/commit/414a9d3cf34c7aff1c63533df4c40ebb63bd0840

Thanks!