On Sunday, November 18, 2012 03:07:01 AM Jeff Davis wrote:
> Process A (process that clears a VM bit for a data page):
>   1. Acquires exclusive lock on data buffer
>   2. Acquires exclusive lock on VM buffer
>   3. clears VM bit
>   4. Releases VM buffer lock
>   5. Releases data buffer lock

Well, but right this is a rather big difference. If vm pages get 
unconditionally locked all the time we will have a huge source of new 
contention as they are shared between so many heap pages.

Andres Freund           http://www.2ndQuadrant.com/
PostgreSQL Development, 24x7 Support, Training & Services

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