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

Author: Stuart Cracraft

Date: 16:44:00 09/21/04

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On September 21, 2004 at 18:01:26, Richard Pijl 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.
>>
>>This is represented by the actual code below.
>>
>>After doing this, I expected least the same result or slightly
>>better (than 250/300 on Win-at-Chess). Instead I scored 248/300
>>(consistently) with Two-Tier and 250/300 consistently with One-Tier.
>>
>>I am asking that some of the talented folks look this over
>>and tell me if this is grossly wrong (expectation -or- code.)
>>
>>Or what might be the best methods for evaluating the function of
>>the two methods...
>>
>
>Replacement schemes start making a difference when entries start to get
>overwritten on a regular basis. So, don't expect a big difference on 1 second
>searches. The overhead of a dual probe (without looking at your code) may hurt
>at such short searches.
>What you can do is reduce the hash size to, lets say 10kb and then compare
>scores again.
>Richard.

I always wondered why aging of entries in the hash table using a timestamp
wouldn't be better.

Stuart




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