Merge "Add DB2 full online backups for DB2"
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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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Sections of this template were taken directly from the Nova spec
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template at:
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https://github.com/openstack/nova-specs/blob/master/specs/juno-template.rst
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..
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This template should be in ReSTructured text. The filename in the git
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repository should match the launchpad URL, for example a URL of
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https://blueprints.launchpad.net/trove/+spec/awesome-thing should be named
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awesome-thing.rst.
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Please do not delete any of the sections in this template. If you
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have nothing to say for a whole section, just write: None
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Note: This comment may be removed if desired, however the license notice
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above should remain.
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====================================
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DB2 Full Online Backup and Restore
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====================================
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Currently in Trove, we support full offline backups for DB2 which is the
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default backup mechanism for DB2. This enables users to take full backups of
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DB2 databases when no applications are connected to or using these databases.
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While useful for cases where this downtime is okay, it is not very useful in
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a production type environment were applications are expected to be online all
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the time. DB2 provides a way to do online backups and this spec outlines how
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we can implement a full online backup mechanism in Trove.
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Launchpad Blueprint:
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https://blueprints.launchpad.net/trove/+spec/db2-online-backup
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Problem Description
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===================
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There are two types of backups we can perform using DB2 - offline and online.
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Offline backups require users and applications to be disconnected from the
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databases thereby requiring a certain down time. Online backups on the other
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hand, can be performed while users are still connected to databases. Trove
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currently supports full offline backups for DB2. In this spec, we explain
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how to enable full online backups for DB2 in Trove.
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Proposed Change
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===============
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As mentioned above, the difference between offline and online backup is that
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in the former case all applications must disconnect from the database while
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in the latter, applications can still be connected to databases while backup
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is being taken. In order to enable online backups, archive logging needs to
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be enabled. This allows applications to use the database even while backups
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are being taken. Any updates made to the database is recorded in the logs.
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Logging is a mechanism where every updates to a database is recorded to
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transaction logs (also called active logs) as the data is being modified.
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There are 2 types of logging mechanism - circular and archive logging. By
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default, circular logging is enabled which means that after the last active
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log is filled, the first active log is overwritten. With circular logging
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as the default logging mechanism, only offline backups can be taken.
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Using archive logging, the logs are stored in sequence and as logs get full,
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they are archived. Archive logging allows users to restore databases by roll
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forwarding to a particular point in time or a point before failure. Hence,
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users can restore a database from a backup image and roll forward to a
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particular point using logs thus getting it to a consistent state. For an
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introduction to archive logging, please refer [1] and for an overview of how
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transactional logging works in DB2, please refer [2].
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To enable full online backup for Trove, the following steps need to be taken:
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1. Create a directory to store the backups and archive logs -
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/home/db2inst1/db2inst1/backup/ArchiveLogs
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2. When a database is created, if online backups is configured for DB2(through
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the backup_strategy config property), then configure the following database
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configuration parameter: 'LOGARCHMETH1' to point to a location where the
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archive logs can be stored using the command:
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db2 update database configuration for <db> using LOGARCHMETH1
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'DISK:/home/db2inst1/backup/ArchiveLogs'
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Setting this database configuration parameter enables archive logging and
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stores the archive logs in a location different from the primary/active
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logs.Once this change is made, a full offline backup needs to be taken
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before any connections can be made to the database (this is because the
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database goes into a 'BACKUP_PENDING' state when this configuration
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change is made).
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db2 backup database <db> to /home/db2inst1/db2inst1/backup
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This backup can be deleted from the backup directory after this operation.
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3. The online backup strategy for DB2 will comprise of the following actions:
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- Check if archive logging is enabled for each database
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- Check if there is enough space to store backups (which will include
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database and archived logs). The get_dbsize_info function that DB2
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provides can be used to get the size of the database directory. We can
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query the SYSIBMADM.LOG_UTILIZATION table to get the log space used for
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each database.
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- Do an online backup of the database and include the archive logs along
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with the backup image itself:
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db2 backup database <db> ONLINE to
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/home/db2inst1/db2inst1/backup INCLUDE LOGS
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4. Once the backup is complete, compress/encrypt the backup inside the volume
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storage.
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5. The compressed/encrypted file can then be stored in Swift under the
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database_backups container.
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6. Once the backups are stored in Swift, we can go ahead and delete the backup
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files and archive logs from the backup directory.
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Restoring a database includes restoring from an online backup image and
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rolling forward the logs to the end of the backup to make sure the database is
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in a consistent state.
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1. Create a directory where the backup files and archive logs can be stored
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2. Retrieve the backup from storage to the proper location
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3. Use the following commands to restore the database and ensure it is in a
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consistent state:
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- db2 RESTORE DATABASE <db> FROM <backup_dir> LOGTARGET <log_dir>
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The above command restores the database from the specified online backup
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directory and extracts the archive log files into the log_dir
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- db2 ROLLFORWARD DATABASE <db> TO END OF BACKLOG AND COMPLETE
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This command will roll forward the restored database to a consistent state
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by applying the archive logs. To see more details on the ROLLFORWARD
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command, please refer [3].
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Configuration
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-------------
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The default configuration values of the following will need to change to
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correspond to the respective DB2 locations.
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* backup_strategy
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* backup_namespace
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* restore_namespace
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Database
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--------
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None
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Public API
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----------
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None
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Public API Security
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-------------------
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None
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Python API
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----------
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None
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CLI (python-troveclient)
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------------------------
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None
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Internal API
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------------
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None
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Guest Agent
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-----------
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The DB2 guestagent will be modified to add support for full online backup
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and restore functionality. In addition, new strategies will also be added
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to support these new features.
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The following guestagent files will be modified:
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- trove/guestagent/datastore/experimental/db2/service.py
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- trove/guestagent/datastore/experimental/db2/system.py
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and the following new strategy files will be modified to add a new class
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for online backups:
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- trove/guestagent/strategies/backup/experimental/db2_impl.py
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- trove/guestagent/strategies/restore/experimental/db2_impl.py
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New classes will be added for online backup strategy and the existing
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class needs to be renamed from DB2Backup -> DB2OfflineBackup
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Alternatives
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------------
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None
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Dashboard Impact (UX)
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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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Mariam John (johnma)
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Milestones
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----------
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Newton
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Work Items
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----------
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There will only be one work item for this feature. This includes implementing
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the strategies for DB2 online backup and restore and make the necessary
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guestagent changes. This will also include test-cases necessary to test the
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new functionalities.
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Upgrade Implications
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====================
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None
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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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* Add new test cases to test online backup and restore functionality for DB2:
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- Add new unit tests to test the newly implemented functionality
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- Add a new DB2 helper class to the existing integration-test framework.
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Documentation Impact
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====================
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The datastore documentation should be updated to reflect the enabled features.
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References
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==========
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.. [1] https://www.ibm.com/support/knowledgecenter/SSEPGG_10.5.0/com.ibm.db2.luw.admin.ha.doc/doc/c0051344.html
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.. [2] http://www.ibm.com/developerworks/data/library/techarticle/0301kline/0301kline.html
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.. [3] https://www.ibm.com/support/knowledgecenter/SSEPGG_10.5.0/com.ibm.db2.luw.admin.cmd.doc/doc/r0001978.html
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Appendix
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========
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None
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