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Subject: Re: Two-Tier Hashtable vs. One-Tier

Author: martin fierz

Date: 15:02:50 09/22/04

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On September 22, 2004 at 13:07:22, Michael Henderson wrote:

>On September 22, 2004 at 05:10:56, martin fierz wrote:
>
>>On September 21, 2004 at 17:36:47, Stuart Cracraft wrote:
>>
>>>Hi -- this past weekend I switched from single-tier replace
>>>always to two-tier place 1st tier in 2nd if incoming position
>>>is searched to a >= depth than currently stored at hash entry
>>>and store incoming position in 1st tier, otherwise always replace
>>>2nd tier if depth is.
>>[snip]
>>
>>i use only one hashtable in my program. whenever i tried using 2 tables, my
>>results were worse. i tried this many times, because everybody here says it's
>>better to use 2 tables. i never got it working, and decided to stick with 1
>>table, as it is much simpler overall.
>>
>>IIRC dieter buerssner also mentioned that for him 1 table worked just as well as
>>2 tables.
>>
>>as others have said, if you want to benchmark this you'll have to use longer
>>searches - and to do that you should use a different test than WAC, i suggest
>>using ECMGCP, that is much tougher and more suited for longer searches. you
>>could also artificially create lots of replacements by making the hashtable(s)
>>really small - but i'm not sure that that will give you a relevant result...
>>
>>cheers
>>  martin
>
>What replacement strategy do you use for the 1 table?
>
>Michael

IIRC i have 4 entries per index, and i always replace the one with the lowest
depth; even if the new entry has a lower depth than any of the 4 existing
entries. IIRC because 4 is a #define in my program, i can change that to
anything i like.

it's possible that my 2-table approach was flawed of course. i just never got it
working better than the simple approach above. KISS...

cheers
  martin



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