Messages in this thread | | | Date | Fri, 23 Feb 2001 03:49:05 +0100 (MET) | From | Andries.Brouwer@cwi ... | Subject | Re: [rfc] Near-constant time directory index for Ext2 |
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Just looking at R5 I knew it wasn't going to do well in this application because it's similar to a number of hash functions I tried with the same idea in mind: to place similar names together in the same leaf block. That turned out to be not very important compared to achieving a relatively high fullness of leaf blocks. The problem with R5 when used with my htree is, it doesn't give very uniform dispersal.
The bottom line: dx_hack_hash is still the reigning champion.
Now that you provide source for r5 and dx_hack_hash, let me feed my collections to them. r5: catastrophic dx_hack_hash: not bad, but the linear hash is better.
E.g.: Actual file names:
Linear hash, m=11, sz=2048, min 262, max 283, av 272.17, stddev 12.25 dx_hack_hash: sz=2048, min 220, max 330, av 272.17, stddev 280.43 r5: sz=2048, min 205, max 382, av 272.17, stddev 805.18
Linear hash, m=11, sz=65536, min 0, max 24, av 8.51, stddev 8.70 dx_hack_hash: sz=65536, min 0, max 23, av 8.51, stddev 8.51 r5: sz=65536, min 0, max 26, av 8.51, stddev 8.89
Generated consecutive names:
Linear hash, m=11, sz=2048, min 262, max 283, av 272.17, stddev 12.25 dx_hack_hash: sz=2048, min 191, max 346, av 272.17, stddev 636.11 r5: sz=2048, min 0, max 3587, av 272.17, stddev 755222.91
Linear hash, m=11, sz=65536, min 2, max 14, av 8.51, stddev 2.79 dx_hack_hash: sz=65536, min 0, max 26, av 8.51, stddev 12.24 r5: sz=65536, min 0, max 120, av 8.51, stddev 738.08
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