[EP-tech] Re: mysqldump problem with cachetables

Malcolm Bodger M.Bodger at westminster.ac.uk
Mon Apr 22 14:26:49 BST 2013


Many thanks Tim, Paolo and Mark,

I do run it as an overnight backup, but sometimes it fails because of the missing cache tables, clearly removed during the dump. The machine is a virtual machine which are all backed up via snapshots overnight, but I plan to use the dumpfile to create our new Eprints server. It did actually work last night, but I'm still suprised to have, currently, 1075 cache tables. Anyway, thanks again.

Regards,
Malcolm.

________________________________________
From: eprints-tech-bounces at ecs.soton.ac.uk [eprints-tech-bounces at ecs.soton.ac.uk] on behalf of Tim Brody [tdb2 at ecs.soton.ac.uk]
Sent: 22 April 2013 09:16
To: eprints-tech at ecs.soton.ac.uk
Subject: [EP-tech] Re: mysqldump problem with cachetables

mysqldump does a "SHOW TABLES" then goes through each table to dump it. Of
course, a table can be dropped in the mean-time which will confuse it.

So either you have to modify mysqldump to obtain a global lock (not so good
for users) or force it to skip-over lost cache tables.

The better long-term solution is to use InnoDB tables and a file-system
level backup, but that can come with its own problems.

--
All the best,
Tim.

On Mon, 22 Apr 2013 13:40:50 +1000, Mark Gregson <mark.gregson at qut.edu.au>
wrote:
> If you are running myisam table engine, you could try myisamchk
> (http://dev.mysql.com/doc/refman/5.0/en/myisamchk.html) to check for
> underlying table problems.
>
> Is it possible that EPrints is cleaning up (dropping) cache tables while
> mysqldump is running?
>
> Mark
>
> Mark Gregson | Applications and Development Team Leader
> Library eServices | Queensland University of Technology
> Level 3 | R Block | Kelvin Grove Campus | GPO Box 2434 | Brisbane 4001
> Phone: +61 7 3138 3782 | Web: http://eprints.qut.edu.au/
> ABN: 83 791 724 622
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>
>
>
> -----Original Message-----
> From: eprints-tech-bounces at ecs.soton.ac.uk
> [mailto:eprints-tech-bounces at ecs.soton.ac.uk] On Behalf Of Malcolm Bodger
> Sent: Saturday, 20 April 2013 12:19 AM
> To: paolo.tealdi at polito.it
> Cc: <eprints-tech at ecs.soton.ac.uk>
> Subject: [EP-tech] Re: mysqldump problem with cachetables
>
> Hi Paolo,
>
> I'm running mysqldump with the force option and I have 15 lines of error
> mesages, like this one:
>
> Error: Couldn't read status information for table cache1813265 ()
> mysqldump: Couldn't execute 'show create table `cache1813265`': Table
> 'eprints.cache1813265' doesn't exist (1146)
>
> Can I ignore these errors?
>
> Thanks.
> Regards,
> Malcolm.
> ________________________________________
> From: Malcolm Bodger
> Sent: 19 April 2013 15:07
> To: paolo.tealdi at polito.it
> Cc: <eprints-tech at ecs.soton.ac.uk>
> Subject: RE: [EP-tech]  mysqldump problem with cachetables
>
> Hi Paolo,
>
> Thanks for this information, it's very helpful, and I'll go with the
> 'force' option.
>
> Regards,
> Malcolm.
> ________________________________________
> From: Paolo Tealdi [paolo.tealdi at polito.it]
> Sent: 19 April 2013 14:23
> To: Malcolm Bodger
> Cc: <eprints-tech at ecs.soton.ac.uk>
> Subject: Re: [EP-tech]  mysqldump problem with cachetables
>
> Il 19/04/2013 15:01, Malcolm Bodger ha scritto:
>> Hi Paolo,
>>
>> I run the cleanup_cachemaps, but it only removed one orphaned table,
>> leaving me with 942.
>> Would you know why I have so many cache tables?
>>
>> Thanks.
>> Regards,
>> Malcolm.
>>
>
> Hi Malcom,
> This is normal.
> When you make a web search on your eprints web interface, the system
saves
> the result records in a cache table, avoiding to repeat a (possibly) cpu
> intensive operation (for example to present the next search page).
> The server saves the recordset result in a table named "cache$number" and
> adds a line also in "cachemap" table.
> The epadmin command i wrote matches the records in "cache" table with the
> cache"number" table,  cleaning orphaned table (NOT all cache table on the
> orphaned one).
> The server has a setting for the max number of cache table active, when
you
> go beyond that number, automatically the server drops the oldest table
> "table$number" and deletes its related record in "cachemap" table.
> The error you find in the mysqldump is due to this automatic cache
cleaning
> by eprints: mysqldump tries to dump a table that eprints has already
> deleted.
> I think it's not a problem if you put --force in the mysqldump
parameters.
>
>
> Best regards,
> Paolo Tealdi
>
>
> --
> Ing. Paolo Tealdi         Area IT - Politecnico Torino
> Telefono/Phone : +39-011-0906714 , FAX : +39-011-0906799
Indirizzo/Address
> : C.so Duca degli Abruzzi,  24 - 10129 Torino - ITALY Skype :
tealdi.paolo
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--
All the best,
Tim.
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