DDevelopment & Design

mount.ntfs high cpu ubuntu

My computer suffers from sudden and continous hard drive load strokes. Sometimes it lasts for a few minutes and hence work is impossible because everything goes very slow.I’m trying to locate the cause because it makes me nervous :)Today I found one of…

My computer suffers from sudden and continous hard drive load strokes. Sometimes it lasts for a few minutes and hence work is impossible because everything goes very slow.
I’m trying to locate the cause because it makes me nervous :)

Today I found one of the causes. It’s updatedb.mlocate script which is responsible for scanning hard drives and build locate (a location of files) database. But due to some NTFS driver limitations that poor thing thinks that NTFS share is always new and needs to be rescan at every scheduled scan.

How to make sure that you have the same problem? When hard drive starts to choke check all IO processes with

sudo iotop

and look for updatedb.mlocate or mount.ntfs processes with high IO load. If this is the case try to fix it.
The solution is to point NTFS shares as non-scannable. To do this edit

/etc/updatedb.conf

and add your NTFS mount paths to PRUNEPATHS list. Although NTFS is listed in PRUNEFS entry that dummy mlocate script still would scan NTFS shares.

All that I found on Ubuntu forum.

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DDevelopment & Design

Simple trick to DRY your Grails controller

Grails controllers are not very DRY. It's easy to find duplicated code fragments in default generated controller. Take a look at code sample below. It is duplicated four times in show, edit, update and delete actions:

class BookController {
def show() {
def bookInstance = Book.get(params.id)
if (!bookInstance) {
flash.message = message(code: 'default.not.found.message', args: [message(code: 'book.label', default: 'Book'), params.id])
redirect(action: "list")
return
        }
        [bookInstance: bookInstance]
    }
}

Why is it duplicated?

There is a reason for that duplication, though. If you move this snippet to a method, it can redirect to "list" action, but it can't prevent controller from further execution. After you call redirect, response status changes to 302, but after method exits, controller still runs subsequent code.

Solution

At TouK we've implemented a simple trick to resolve that situation:

  1. wrap everything with a simple withStoppingOnRender method,
  2. whenever you want to render or redirect AND stop controller execution - throw EndRenderingException.

We call it Big Return - return from a method and return from a controller at once. Here is how it works:

class BookController {
def show(Long id) {
withStoppingOnRender {
Book bookInstance = Book.get(id)
validateInstanceExists(bookInstance)
            [bookInstance: bookInstance]
        }
    }

protected Object withStoppingOnRender(Closure closure) {
try {
return closure.call()
        } catch (EndRenderingException e) {}
    }

private void validateInstanceExists(Book instance) {
if (!instance) {
flash.message = message(code: 'default.not.found.message', args: [message(code: 'book.label', default: 'Book'), params.id])
redirect(action: "list")
throw new EndRenderingException()
        }
    }
}

class EndRenderingException extends RuntimeException {}

Example usage

For simple CRUD controllers, you can use this solution and create some BaseController class for your controllers. We use withStoppingOnRender in every controller so code doesn't look like a spaghetti, we follow DRY principle and code is self-documented. Win-win-win! Here is a more complex example:

class DealerController {
@Transactional
def update() {
withStoppingOnRender {
Dealer dealerInstance = Dealer.get(params.id)
validateInstanceExists(dealerInstance)
validateAccountInExternalService(dealerInstance)
checkIfInstanceWasConcurrentlyModified(dealerInstance, params.version)
            dealerInstance.properties = params
saveUpdatedInstance(dealerInstance)
redirectToAfterUpdate(dealerInstance)
        }
    }
}