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 Post subject: How slow is slow delete?
PostPosted: Sun Jun 20, 2010 9:29 am 
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Location: Little Rock
Recently I discovered my cable provider shifted the majority of my channels from analog to QAM256. After sorting that mess out and getting my channels back, I went through the recorded programs in MythWeb and chose "Delete + Rerecord" for every show worth of static I'd recorded off of nonexistent channels.

I did that at about midnight last night. Today at 10:20am the majority of the programs are still showing up in MythWeb and in View Recorded programs. Rather than choosing all of the old programs again I started with one show that had 7 bad episodes. I chose delete and rerecord on all 7 then refreshed the MythWeb page. All 7 episodes were back.

I searched for the programs in /myth/pretty and all were there. I listed the linked files in /myth/tv and they were also there.

A few minutes later mythweb started knocking off the programs one by one. Within 20-30 minutes all 7 recordings were gone. The files in /myth/tv were deleted but the "pretty" entries still existed.

Apparently this behavior is as expected with the slow delete option checked. However, why were none of the programs deleted in the 10 hours since I first deleted them last night?

I checked the backend log for overnight and right after deleting each of the 7 files I re-selected this morning, and there's nothing related to the delete. No error of any kind mentioning permissions or that the file can't be found; there is simply nothing mentioning the program name or file name or the word error.

Also, does slow delete really cause the behavior where you delete a file, it reappears in the program listing, and then disappears when it finally deletes? It drives my wife crazy because she thinks the program is not being deleted and keeps trying. It would be nice if it stayed gone from the listings until the system got around to deleting it.


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 Post subject:
PostPosted: Sun Jun 20, 2010 9:50 am 
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Update: the short answer is yes, it is that slow.

My BE isn't doing anything now so I turned off the slow delete option. I started going through the programs again and re-deleting them in MythWeb. Each time I deleted the programs and refreshed the page the deleted program would briefly appear again, but then in less than 10 seconds it would be gone and not return. Then, while I paused to look at something else, 6 shows I deleted last night disappeared from Mythweb (I hadn't re-selected them this morning).

I guess the moral of the story is patience, grasshopper, they will delete.

I still think the program names should stay gone from the recorded programs list when you've chosen to delete them. Having them re-appear and disappear isn't very user friendly.


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 Post subject:
PostPosted: Sun Jun 20, 2010 7:52 pm 
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Location: Bendigo, Victoria, Australia
What version of Knoppmyth / LinHES are you running?
I use "slow delete" on my R5.5 machine and when I tell it to delete programs they disappear from the UI immediately. They are still on the filesystem until they are slow deleted but gone from Mythfrontend and Mythweb.

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 Post subject:
PostPosted: Mon Jun 21, 2010 5:47 am 
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I'm on LinHes 6.02 (I think) with MythTV 0.22 (for sure).


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 Post subject:
PostPosted: Mon Jun 21, 2010 4:55 pm 
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Location: middleton wi usa atsc
turpie wrote:
I use "slow delete" on my R5.5 machine and when I tell it to delete programs they disappear from the UI immediately. They are still on the filesystem until they are slow deleted but gone from Mythfrontend and Mythweb.

I am using R6.03 upgraded from 6.02 and I get the same result as turpie


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 Post subject:
PostPosted: Mon Jun 21, 2010 5:42 pm 
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What filesystem are you using? I would think this could play a big part.

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 Post subject:
PostPosted: Mon Jun 21, 2010 5:47 pm 
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Location: middleton wi usa atsc
ext3


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 Post subject:
PostPosted: Mon Jun 21, 2010 5:50 pm 
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OP here, I'm using XFS.


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 Post subject:
PostPosted: Mon Jun 21, 2010 6:41 pm 
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DoomedTX wrote:
OP here, I'm using XFS.


And although I'm now learning that untweaked XFS is possibly the worst performer when it comes to deletes, I've been using XFS for years and only just recently experienced the problem where deleted programs pop up again in the UI and then disappear again. I'm thinking there's got to be something related to the DB that causes this behavior. Opinions?


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 Post subject:
PostPosted: Tue Jun 22, 2010 2:11 am 
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Location: London, UK
Hi DoomedTX,

Just wanting to know - how do you mean that
Quote:
untweaked XFS is possibly the worst performer when it comes to deletes

I've been using XFS for years too - it strength was meant to be in deleating large files.

Regards Tophee

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 Post subject:
PostPosted: Tue Jun 22, 2010 5:37 am 
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tophee wrote:
Hi DoomedTX,

Just wanting to know - how do you mean that
Quote:
untweaked XFS is possibly the worst performer when it comes to deletes

I've been using XFS for years too - it strength was meant to be in deleating large files.

Regards Tophee


Well, according to the Google search results for "xfs slow delete," by default XFS is much slower than ext3 or ReiserFS at deleting files of any size. It's better able to deal with the large files associated with Myth recordings, hence the reason it was recommended to me and I switched, but it is slower at it.

When I'm a bit closer to the computer (I'm at the tail end of a 6-month tour in Colombia) I might try some tweaks to xfs to speed it up, but I'm still wondering if that's really the root cause since 1) I've never experienced this with XFS before and 2) deleted programs should never reappear in the UI even if the file hasn't been deleted yet.


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 Post subject:
PostPosted: Tue Jun 22, 2010 6:05 am 
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I've always used XFS and never had the problems you are describing (touches wood...)

Martian

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 Post subject:
PostPosted: Tue Jun 22, 2010 9:15 am 
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Location: London, UK
I've not noticed any major problems in speed of deleting things, but I've not really paid much attention to it. But as I've 1.4Tb of recording space, generally it takes a long while to fill up with recordings.

I may be imagining it but I thought XFS is bad at deleting lots of small files, but good at large.

I'd be interested in seeing what improvements your tweeks would make and I agree deleted programs should disappear, never to reappear once deleted.

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 Post subject:
PostPosted: Tue Jun 22, 2010 9:32 am 
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I moved from ext3 and having to use the slow delete option to xfs with the slow delete option turned off years ago and haven't experienced what you are describing. With ext3 playback would shudder when recordings would expire until I started using the slow delete option and then moved to xfs. Have you tried turning off the slow delete option?


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 Post subject:
PostPosted: Tue Jun 22, 2010 4:28 pm 
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Location: Little Rock
brfransen wrote:
I moved from ext3 and having to use the slow delete option to xfs with the slow delete option turned off years ago and haven't experienced what you are describing. With ext3 playback would shudder when recordings would expire until I started using the slow delete option and then moved to xfs. Have you tried turning off the slow delete option?


Yep, as I mentioned in post 2, I tried deleting files with slow delete off. They still reappeared and then disappeared from the list. I think xfs is a red herring and the real answer lies somewhere else. Unfortunately my mysqld.log file was 0 bytes so no help there. Nothing relevant in the mythfrontend or backend logs. I wonder where else I can look.


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