Problem with ufs not releasing vm_pages on busy volume. (soft updates related)

[Q]

On 02/08/2006, at 8:10 PM, Q wrote:

> I have a problem that seems to be related to something ufs related  
> not releasing some vm_pages on busy filesystems. I have two servers  
> running PostgreSQL, one running 6.0-RELEASE, the other 6.1-RELEASE.  
> Both are under the same (fairly heavy) load, performing the same  
> operations in bursts every five minutes. The filesystems in  
> question are 450-500Gig, each server using a different brand of  
> RAID card, they both have soft-updates enabled.
>
> The problem is that both servers are seeing an accumulation of  
> about 100Mb of active pages per day (looking at  
> vm.stats.vm.v_active_count) that never get released. The only way  
> to release these pages is to unmount the filesystem and remount it.  
> Failing to do this results in the server eventually locking up.
>
> If someone could provide me with some direction on how to go about  
> tracking down what might be causing this to happen it would be much  
> appreciated.

I have narrowed the cause of this issue down further to something to  
do with soft updates. If I turn off soft updates for the filesystem  
hosting the database the system no longer accumulates active vm_pages  
constantly. Instead for accumulating 100Mb a day of active vm pages  
until all memory is consumed, it will hover around 50-60Mb with soft  
updates disabled.

If someone familiar with the softupdates code is willing to help me  
pinpoint the cause of this problem it would be much appreciated.

-- 
Seeya...Q

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                           _____  /  Quinton Dolan - qdolan at gmail.com
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