Messages in this thread | | | From | "Stephen C. Tweedie" <> | Date | Fri, 30 Apr 1999 01:08:32 +0100 (BST) | Subject | Re: 2.2.6_andrea2.bz2 |
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Hi,
On Tue, 27 Apr 1999 02:38:02 +0200 (CEST), Andrea Arcangeli <andrea@e-mind.com> said:
> Agreed. I just said Chuck that I would have extracted the rbtree patch > against 2.2.6. I _completly_ agree and right now I am also _very_ worried > by performances of RB in the buffer cache. The rb-cache per-inode is > almost sure a win according to me,
I don't see that as such a sure thing.
With a page cache hash, we can dynamically increase the hash table size with memory size to keep a bound on the expected number of pages per hash bucket. That, plus the natural low complexity of hashing, is good for predictable performance.
Once you have something like Oracle or an LDAP server serving out multi-megabyte data files, the equivalent btree is going to get awefully deep awefully quickly, and there's no simple way to expand the width of the tree dynamically to minimise that cost.
In other words, I can throw memory at hashing to make it faster, but trees have a fixed cost which necessarily grows with their size.
--Stephen
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