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From: Ivan Voras <ivoras@freebsd.org>
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Subject: lseek() scalability and PostgreSQL
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Interesting tidbit from PostgreSQL optimization:

http://rhaas.blogspot.com/2011/11/linux-lseek-scalability.html

"""
PostgreSQL calls lseek quite frequently (to determine the file length, 
not to actually move the file pointer), and due to the performance 
enhancements in 9.2devel, it's now much easier to hit the contention 
problems that can be caused by frequently acquiring and releasing the 
inode mutex.  But it looks like this should be fixed in Linux 3.2, which 
is now at rc1, and therefore on track to be released well before 
PostgreSQL 9.2.
"""

It looks like this might cause some of the things I've observed on 
many-core servers.