Reuse the deleted image-member before create a new one
A specification for reusing the deleted image-member before create a new one. Use only one record to maintain the member-ship between a pair of image and tenant. When create a new image-member, at first check all existing image-member records including the deleted image-member, then update it if it exists, otherwise, create a new one. APIImpact Change-Id: Ie4851ea67d75f346efceb47099a7b8a64f1b5512 Implements: bp reuse-the-deleted-image-member
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Long Quan Sha
Nikhil Komawar
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This work is licensed under a Creative Commons Attribution 3.0 Unported
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License.
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http://creativecommons.org/licenses/by/3.0/legalcode
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======================================================
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Reuse the deleted image-member before create a new one
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======================================================
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https://blueprints.launchpad.net/glance/+spec/reuse-the-deleted-image-member
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Check the deleted image-member before create a new one, then update it if it
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exists, otherwise, create a new one.
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Problem description
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===================
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If glance backend database is not MySQL or postgreSQL,the unique constraint
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of image-member only includes image-id and member. In this case, if an
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image-member is deleted, then create it again with the same parameters, glance
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initiates a query to see if there is already an existing one, but the
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result does not include the record which was marked as deleted, glance will
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try to create a new one with the same parameters, then it will fail with
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duplicate error.
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Proposed change
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===============
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Use only one record to maintain the member-ship between a pair of image and
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tenant. When create a new image-member, at first check all existing
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image-member records including the deleted image-member, then update it if it
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exists, otherwise, create a new one.
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Alternatives
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------------
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Unify the unique constraint for image-member like we did for MySQL and
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postgreSQL in 022_image_member_index.py, it has migrated unique constraint of
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image-member for MySQL and postgreSQL, now its unique constraint includes
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image-id, member and deleted_at. Currently the column "deleted_at" is
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nullable. For other databases like DB2, its unique constraint is more
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restricted than MySQL. The columns under unique constrains should be
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"NOT NULL", otherwise, an error occurs. Thus, we can not create the same unique
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constraint for this kinds of database.
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We would alter "deleted_at" column to "not nullable" in migration. That means
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we have to insert a default timestamp value for the new created image-member,
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an active member with a no-blank timestamp for "deleted_at" would confuse
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user.
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Another solution is migrating the unique constraint from (image-id, member,
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deleted_at) to (image-id, member,created_at) for MySQL and postgreSQL, from
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(image-id, member) to (image-id, member,created_at) for other databases.
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created_at is not nullable, so the new constraint will be applicable to all
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databases. This solution needs data migration for different database.
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Data model impact
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-----------------
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None
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REST API impact
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---------------
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None
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Security impact
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---------------
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None
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Notifications impact
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--------------------
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None
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Other end user impact
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---------------------
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None
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Performance Impact
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------------------
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When create a new image-member, it will search all image-member records
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including the deleted items. But if we enable this patch, it will very rare to
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see many deleted image-member, as the membership will be kept by only one
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record. The only case is, multiple deleted image-members were created before
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applying this patch, we could make a migration script in another patch to
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remove them.
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Other deployer impact
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---------------------
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Configuration options will change:
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None
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Developer impact
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----------------
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None
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Implementation
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==============
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Assignee(s)
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-----------
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Primary assignee:
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Long Quan Sha
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Reviewers
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---------
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Core reviewer(s):
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nikhil-komawar
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Ian Cordasco
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Other reviewer(s):
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Kamil Rykowski
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Abhishek Kekane
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Work Items
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----------
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* Reuse the deleted image-member when create a new one
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Dependencies
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============
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None
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Testing
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=======
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* Verify the deleted image-member is updated when create a new one
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Documentation Impact
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====================
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None
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References
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==========
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Proposed patch:
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https://review.openstack.org/190895
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unique constraint for PostgreSQL, the same as MySQL:
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http://www.postgresql.org/docs/8.1/static/ddl-constraints.html
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unique constraint for DB2:
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https://www-01.ibm.com/support/knowledgecenter/SSEPGG_9.7.0/com.ibm.db2.luw.admin.dbobj.doc/doc/c0020151.html
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