Messages in this thread | | | Date | Thu, 22 Feb 2001 00:26:48 +0100 | From | Jamie Lokier <> | Subject | Re: [rfc] Near-constant time directory index for Ext2 |
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Martin Mares wrote: > Hello! > > > True. Note too, though, that on a filesystem (which we are, after all, > > talking about), if you assume a large linear space you have to create a > > file, which means you need to multiply the cost of all random-access > > operations with O(log n). > > One could avoid this, but it would mean designing the whole filesystem in a > completely different way -- merge all directories to a single gigantic > hash table and use (directory ID,file name) as a key, but we were originally > talking about extending ext2, so such massive changes are out of question > and your log n access argument is right.
A gigantic hash table has serious problems with non-locality of reference. Basically any regular access pattern you started with is destroyed. This is a problem with pageable RAM, let alone disks with millisecond seek times.
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