image-delete fires multiple queries to delete its child entries

[Venkatesh Sampath]

While deleting an image all its child entries are also deleted.

Child entries types are image_locations, image_properties, image_members and image_tags

Currently, for deleting the child entries the following is done:
1. Fire a select query to fetch the child entries.
2. Enumerate through the entries and fire soft-delete (update query) on each child entry seperately.

If the number of child entries grows higher, then the amount of queries fired to delete them grows equally higher essentially increasing the response time for image delete.

This impelementation can be changed to fire one db query for all the child entries corresponding to a particular child entry type.

eg., instead of invoking model.soft_delete(), we can use model_query(CHILD_ENTRY_TYPE).filter(some_condition).soft_delete().

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: master
Review: https://review.openstack.org/37214

[Zhi Yan Liu (lzy-dev)]

Hello venkateshsampath since I have commit a change (#41311) which base on you this commit (#37214), that caused Hudson reassign this item to me automatically. I have tried to correct it and reassign this to you but seems I can do that successful. I'm sorry for this.

[OpenStack Infra (hudson-openstack)]

Reviewed: https://review.openstack.org/37214
Committed: http://github.com/openstack/glance/commit/c7e9786aa777eb6a44a9b9350da587546c347c7a
Submitter: Jenkins
Branch: master

commit c7e9786aa777eb6a44a9b9350da587546c347c7a
Author: Venkatesh Sampath <email address hidden>
Date: Tue Jul 16 16:27:09 2013 +0530

    image-delete fires multiple queries to delete its child entries

    1. Changed individual query calls for soft-deleting the image's
       child entries to one db query call for all child entries of a
       given type.
    2. Added a fix to simple db's 'image_destroy' api to clear
       the location entries.

    Fixes bug 1201758

    Change-Id: Ib673de5460d59ea3af74553048ffcf74dccbdc36

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