[mythtv-commits] Ticket #4760: Use a script for the database backup

[MythTV]

#4760: Use a script for the database backup
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 Reporter:  sphery <mtdean at thirdcontact.com>  |       Owner:  ijr    
     Type:  patch                             |      Status:  new    
 Priority:  minor                             |   Milestone:  unknown
Component:  mythtv                            |     Version:  head   
 Severity:  medium                            |     Mlocked:  0      
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 The attached patch, mythtv-database_backup_using_script.patch , modifies
 the new automatic database backup functionality to invoke a script
 (potentially a distro-specific script) to create the database backup.
 It's primary purpose is to allow packagers to customize the database
 backup procedure and to remove the code in myth calling the externally-
 provided binaries, mysqldump and gzip.  It also has the additional
 advantage of allowing users to perform database backups whenever desired
 (i.e. in startup/shutdown scripts, in a cron job, ...) in such a way that
 the automatically-created database backups are no different from the
 manually-created backups.

 The script path can be specified with the "undocumented" setting
 "DatabaseBackupScript" (default value gContext->GetShareDir() +
 "database_mythconverg_backup.sh").  A matching script
 (gContext->GetShareDir() + "database_mythconverg_restore.sh") can be used
 by the user to restore the database from a backup created by
 database_mythconverg_backup.sh.  If either script is customized by the
 packager, the other script should be tested to verify it works with the
 other.  This way, any distribution-specific backup/restore
 parameters/techniques can be hidden within the scripts, yet the MythTV
 HOWTO can provide generic guidance on backing up and restoring the
 database.

 To prevent the user from having to configure the database within MythTV
 and within the database backup script, a temporary database information
 file is created with name=value pairs specifying dbHostName, dbPort,
 dbUserName, dbPassword, dbName, dbSchemaVer, dbBackupDirectory, and
 dbBackupFilename.  The information file is written with only read by owner
 filesystem permissions and is deleted immediately after execution of the
 backup script.

 The database information file provides the dbBackupDirectory to ensure
 that the script can place the backup in the appropriate directory, i.e. as
 specified in the DB Backups storage group.  The dbBackupFilename
 "suggested" filename is also provided for use by the script.  Since it is
 impossible to force the script to use these values, Myth will check for
 the existence of a file in the dbBackupDirectory whose name begins with
 dbBackupFilename, perhaps with additional extensions--such as ".gz".  If
 any files matching the pattern are found, the filename will be returned to
 be used for the GUI messages; if the script uses some other directory or
 filename, the returned filename will be "", thus preventing GUI messages
 specifying the name of the backup file.  To ensure this works, the script
 must provide a proper exit code.

 The backup script is executed with a single command-line argument
 providing the name of the temporary database information file.  The
 restore script will provide "--help" output to help the user determine the
 appropriate command-line arguments to pass the script.

 Example scripts will be provided in the new programs/scripts directory (an
 initial backup script is in the separate patch, mythtv-
 database_backup_scripts.patch ) and will be installed to the sharedir.
 Packagers who customize the scripts are encouraged to create restore
 scripts using similar command-line arguments to those specified in the
 programs/scripts/database_mythconverg_restore.sh script to make usage of
 scripts easier.  If you would like the scripts placed in a different
 location within the source distribution or at install, please let me know.

 Currently, only the database_mythconverg_backup.sh script is provided.  I
 began it as a shell script thinking it would be relatively quick and
 simple, but the script grew ever more complex as I tried to make a
 relatively-secure script that could also be used for "manual" backups.
 The script has already grown large enough that it may make sense to
 rewrite it in Perl.  Please let me know whether a sh-based or Perl-based
 script would be preferable.

 I plan to add code to allow rotation of backups and to allow the user to
 specify default values/configuration in a separate configuration file
 (especially useful for manual execution).  The
 database_mythconverg_restore.sh script will provide full getopts support
 as well as attempt to parse configuration files to determine database
 configuration information.  However, not knowing whether the devs would
 prefer a sh-based approach or a complete rewrite to Perl, I decided to
 upload what I had for review rather than write a bunch more code only to
 have to reimplement it later in another language.  Once the appropriate
 script language is decided, I can finish both scripts rather quickly
 (though I won't have a chance to do much work on them until next weekend--
 around Mar 1).

 Most all of the ideas in here came from Daniel K., Rob S., and Stuart M.
 on IRC.  I'll take responsibility for all the errors, oversights, and bad
 ideas, though.

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Ticket URL: <http://svn.mythtv.org/trac/ticket/4760>
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