UBUNTU 12.04 LTS | Unable to change service plan

[AlkatraZ]

PRODUCT, VERSION, MICROUPDATE, OPERATING SYSTEM, ARCHITECTURE
Ubuntu 12.04.1 LTS x 64, PLESK 11.0.9 Update #24 (on #25 same problem)

PROBLEM DESCRIPTION
Unable to change the service plan.
Home -> Subscriptions -> current subscription -> Changing Plan
I choose my desired plan (custom plan), then I press OK, page freezes.
If I go to the properties of the plan, the synchronization status "Unsynced"
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A similar problem on another server (Ubuntu 12.04.1 LTS x 64)

STEPS TO REPRODUCE
I can give you access to my test server, where the problem is clearly visible.

ACTUAL RESULT
Unable to change the service plan.

EXPECTED RESULT

ANY ADDITIONAL INFORMATION
When on the same server was installed openSUSE, the problem was not there.

 

[IgorG]

Any related error messages from Plesk logs?
http://kb.parallels.com/111283

 

[AlkatraZ]

UPD
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I checked and found out that the above problem occurs if I want to change the plan for the subscription, where a lot of files (10000 - 20000 forum attachments, eg. JPG GIF ZIP etc.).
In this case, the page of plans change is freezes .
After that, you can not change the plan, even those subscriptions with few files.

Before that I was on a server openSUSE, there was no such problem.
I have a powerful server (Core i7, 16Gb RAM) and it does not cause a problem.
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In the attached file is CP error log: /var/log/sw-cp-server/error_log

 

[AlkatraZ]

Problem solved!
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The reason was not optimal MySQL settings in Ubuntu (by default).
After I installed mysqltuner, has tested and corrected the settings, as recommended, the problem was solved.
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In the attached file is optimized (for RAM 16Gb) my.cnf.