Re: Delaylog

Re: Delaylog

[Arkadiusz Miskiewicz]

On Tuesday 14 of September 2010, Fabricio Archanjo wrote:
> Hey all,
> 
>    I just trying delaylog in my server that has a mysql database. When
> i monted my /var/lib/mysql with delaylog option, it showed me:
> "Enabling EXPERIMENTAL delayed logging feature - use at your own
> risk". Ok, i know it's experimental, but what kind of problem could i
> have using delaylog?

... and what problems in case of system hang or power loss when compared to 
nodelaylog mode?

-- 
Arkadiusz Miśkiewicz        PLD/Linux Team
arekm / maven.pl            http://ftp.pld-linux.org/

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Re: Delaylog

[Fabricio Archanjo]

nicee..
Thanks  Arkadiusz,
I thought there was another thing which i did'n know..

On Tue, Sep 14, 2010 at 4:06 PM, Arkadiusz Miskiewicz <arekm@maven.pl> wrote:
> On Tuesday 14 of September 2010, Fabricio Archanjo wrote:
>> Hey all,
>>
>>    I just trying delaylog in my server that has a mysql database. When
>> i monted my /var/lib/mysql with delaylog option, it showed me:
>> "Enabling EXPERIMENTAL delayed logging feature - use at your own
>> risk". Ok, i know it's experimental, but what kind of problem could i
>> have using delaylog?
>
> ... and what problems in case of system hang or power loss when compared to
> nodelaylog mode?
>
> --
> Arkadiusz Miśkiewicz        PLD/Linux Team
> arekm / maven.pl            http://ftp.pld-linux.org/
>
> _______________________________________________
> xfs mailing list
> xfs@oss.sgi.com
> http://oss.sgi.com/mailman/listinfo/xfs
>

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Re: Delaylog

[Stan Hoeppner]

Arkadiusz Miskiewicz put forth on 9/14/2010 2:06 PM:
> On Tuesday 14 of September 2010, Fabricio Archanjo wrote:
>> Hey all,
>>
>>    I just trying delaylog in my server that has a mysql database. When
>> i monted my /var/lib/mysql with delaylog option, it showed me:
>> "Enabling EXPERIMENTAL delayed logging feature - use at your own
>> risk". Ok, i know it's experimental, but what kind of problem could i
>> have using delaylog?
> 
> ... and what problems in case of system hang or power loss when compared to 
> nodelaylog mode?

This was covered in prior posts IIRC.  Delaylog holds more write
transactions in memory in an effort to decrease the amount of disk I/O
and optimize write patterns.  The more blocks waiting in the in memory
log, the more data will be lost due to power outage, controller/disk
failure, storage HBA/network failure (iSCSI/FC), kernel panics, etc.

Same failure modes as before, but with potentially greater loss of
data--unless there is an undiscovered bug that can wreck the entire
filesystem.  ;)  Which I believe is the reason for the "experimental"
boilerplate.

-- 
Stan

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Re: Delaylog

[Fabricio Archanjo]

When i changed to delaylog option my database performance increased,
so how i have 2 databases one master another slave, i can keep it. If
i have problem on my filesystem, i'll need to changed the slave to
master and recover my master.


Thanks all.

On Tue, Sep 14, 2010 at 5:03 PM, Stan Hoeppner <stan@hardwarefreak.com> wrote:
> Arkadiusz Miskiewicz put forth on 9/14/2010 2:06 PM:
>> On Tuesday 14 of September 2010, Fabricio Archanjo wrote:
>>> Hey all,
>>>
>>>    I just trying delaylog in my server that has a mysql database. When
>>> i monted my /var/lib/mysql with delaylog option, it showed me:
>>> "Enabling EXPERIMENTAL delayed logging feature - use at your own
>>> risk". Ok, i know it's experimental, but what kind of problem could i
>>> have using delaylog?
>>
>> ... and what problems in case of system hang or power loss when compared to
>> nodelaylog mode?
>
> This was covered in prior posts IIRC.  Delaylog holds more write
> transactions in memory in an effort to decrease the amount of disk I/O
> and optimize write patterns.  The more blocks waiting in the in memory
> log, the more data will be lost due to power outage, controller/disk
> failure, storage HBA/network failure (iSCSI/FC), kernel panics, etc.
>
> Same failure modes as before, but with potentially greater loss of
> data--unless there is an undiscovered bug that can wreck the entire
> filesystem.  ;)  Which I believe is the reason for the "experimental"
> boilerplate.
>
> --
> Stan
>
> _______________________________________________
> xfs mailing list
> xfs@oss.sgi.com
> http://oss.sgi.com/mailman/listinfo/xfs
>

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Re: Delaylog

[Christoph Hellwig]

On Tue, Sep 14, 2010 at 09:06:24PM +0200, Arkadiusz Miskiewicz wrote:
> On Tuesday 14 of September 2010, Fabricio Archanjo wrote:
> > Hey all,
> > 
> >    I just trying delaylog in my server that has a mysql database. When
> > i monted my /var/lib/mysql with delaylog option, it showed me:
> > "Enabling EXPERIMENTAL delayed logging feature - use at your own
> > risk". Ok, i know it's experimental, but what kind of problem could i
> > have using delaylog?

Basically you could hit a race or lockup in the code under high stress
or unusual workloads.  So far we just had one possible lockup under very
high dbench load.

> ... and what problems in case of system hang or power loss when compared to 
> nodelaylog mode?

The same as with the old log code - if you crash recently written data
might be lost.  Unless a really severe bugs shows up (in either the old
or new code) that only includes data since the last fsync/sync.  The
quantitative difference is that a lot more metadata is now cached in
core, so on a crash you can lose more recently written but not synced
metadata.

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