Hello all,
Sorry if this is a naive question.
I was going through Greg Smith's slides on buffer
cache(http://www.westnet.com/~gsmith/content/postgresql/InsideBufferCache.pdf).
When going through the page replacement algorithm that we use i.e.
clocksweep algorithm, I felt a potential problem in our current
system.
Specifically, when a new entry is allocated in the buffer, it's
USAGE_COUNT is set to 1. On each sweep of the algorithm, the
USAGE_COUNT is decremented and an entry whose USAGE_COUNT becomes
zero is replaced.
I feel that this could lead to a bias towards replacement of
relatively younger pages in the cache over older pages. An entry
which has just entered the cache with USAGE_COUNT=1 could be replaced
soon, but it may be needed frequently in the near future, which would
result in it being repeatedly brought into the cache, leading to
replacement overheads.
I think this is the well known face off between LRU and MRU algorithms.
How do we work around this problem?
Regards,
Atri
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Regards,
Atri
l'apprenant