[mythtv-commits] Ticket #2538: Fix recorded* table cleanup and MySQL3 compatibility

[MythTV]

#2538: Fix recorded* table cleanup and MySQL3 compatibility
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 Reporter:  sphery <mtdean at thirdcontact.com>  |       Owner:  ijr    
     Type:  patch                             |      Status:  new    
 Priority:  minor                             |   Milestone:  unknown
Component:  mythtv                            |     Version:  0.20   
 Severity:  medium                            |  
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 In [10918] cleanup of the recordedprogram, recordedrating, and
 recordedcredits tables was moved into mythfilldatabase's "daily
 housekeeping" section.  Previously, obsoleted data was deleted from these
 tables on a recording-by-recording basis when records were deleted from
 the recorded table; however, there were several ways this approach could
 result in orphaned entries.  Therefore, when the cleanup task was moved to
 mythfilldatabase, it was made to delete any entries for which no recording
 exists in the recorded table.

 Unfortunately, the approach uses a MySQL 4.0+ syntax (multiple table
 UPDATEs and DELETEs--in this case through LEFT JOINs--are not supported
 until MySQL 4.0).  Also--at least on my 4.0.18 database--the query
 silently failed to work (silently since we don't check the result of the
 exec()) due to the error:
 {{{
 mysql> DELETE p FROM recordedprogram p LEFT JOIN recorded r
 > ON p.chanid = r.chanid AND p.starttime = r.progstart
 > WHERE r.chanid IS NULL;
 ERROR 1066: Not unique table/alias: 'p'
 }}}

 because the value of the table alias was not yet determined (it works with
 "DELETE recordedprogram ...").  Therefore, my database contained
 aproximately 150 orphaned entries in each of recordedprogram and
 recordedrating and 1859 entries in recordedcredits, which resulted in
 approximately 150 distinct chanid/starttime's.

 The attached patch fixes this issue and uses a MySQL 3.x-compatible
 approach.  Since the values relate to the recorded table through two
 columns (chanid and starttime), building up a NOT IN query
 programmatically wasn't an option.  However, since MySQL 3.x supports LEFT
 JOINs in SELECT statements, I selected all the orphaned rows and iterated
 over the results deleting each record.  In spite of the fact that I had
 over 2100 rows that resulted in about 450 DELETE statements, the cleanup
 took negligible resources.  Once the initial cleanup is completed, daily
 cleanup should result in deletion of much more reasonable number of rows.
 Also, the initial cleanup will occur almost immediately upon starting the
 backend after upgrade (as described below)--when the user is unlikely to
 be recording a show.

 In addition to the changes described above, the patch moves the cleanup
 function back out of mythfilldatabase and into the housekeeper (as the
 first step in moving cleanup functionality out of mythfilldatabase for the
 EIT-only users).  Per an IRC discussion with Chris Pinkham, I added a
 !DailyCleanup tag to housekeeping and consolidated the two other master-
 backend-only daily cleanup tasks (!CleanupOldJobsInQueue and
 !CleanupAllOldInUsePrograms) into the !DailyCleanup.  Since the
 !DailyCleanup tag won't yet exist on a user's machine, it will ensure the
 intial cleanup is performed when the housekeeping thread is started upon
 backend startup.

-- 
Ticket URL: <http://svn.mythtv.org/trac/ticket/2538>
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