Comment 16 for bug 1731349

Reviewed: https://review.openstack.org/529715
Committed: https://git.openstack.org/cgit/openstack/heat/commit/?id=e5707618f3a5cf22e2f4260ed1aa64b598d3a941
Submitter: Zuul
Branch: master

commit e5707618f3a5cf22e2f4260ed1aa64b598d3a941
Author: Zane Bitter <email address hidden>
Date: Mon Jan 8 17:23:12 2018 -0500

    Avoid always loading nested stack on update

    Previously, when calling StackResource._validate_nested_resources() (which
    we do whenever we create or update a nested stack), we would load the
    nested stack into memory to validate the number of resources in the nested
    stack, unless the max_resources_per_stack config option was set to -1. This
    meant we would load the nested stack into memory in the same engine as the
    parent on every update.

    To reduce the memory high-water mark, fetch the information we need over
    RPC from another engine instead.

    To ensure this is only called once, move the call into the validate code.
    (Previously it was called again in the create/update itself.)

    Change-Id: I78d12ecc8240c697e26893ae2d7172b60883fb93
    Partial-Bug: #1731349