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Subject: Re: Hash table statistics

Author: Robert Hyatt

Date: 11:58:37 04/08/04

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On April 08, 2004 at 14:00:50, Eric Oldre wrote:

>When people talk about there move ordering hitting 90%, what exactly are they
>measuring? is it that on 90% of the nodes the first move tried is the best?

For me, it means that on any node where I fail high, 90% of the time (actually a
bit higher for me, more like 92-93% most of the time) I will fail high on the
first move I search...


>
>what i've been doing is averaging the percentage of moves that i go through
>before i find the best move.
>
>example: if there are 20 moves from a position, and the 2nd move evaluated is
>best, i'd say i had 5%. (or 95%). if the first move is the best, then i have 0%
>(or 100%)
>
>i store the statistics separately depending on whether it's a pv or beta node.
>
>for beta nodes i'm getting a move that causes the cutoff very fast, on average
>after around 2-3 % of the moves.
>
>for PV nodes, i't a bit worse, i don't have the numbers with me, bug it seems if
>i remember right, about 20%. (or 80%)
>
>these seems to make since to me since if the parent node made a big blunder, it
>shouldn't take long to find something that will cause a cut off, but it the
>parent node was a good move, then
>
>so my question is, am i using the "standard" way of measuring move ordering? and
>if not, what is the standard way. so that i can compare apples to apples when
>talking about move ordering.

I don't know if there is a "standard way" at all.  I have been reporting using
"my way" for a long while and it is a simple but easy to understand idea.  IE in
SMP search, it doesn't matter whether a PV or non-PV move has bad move ordering,
all that matters is that you parallel search at a node where all branches need
to be searched.  The higher "my" percentage, the more likely you are to make a
good parallel search split decision...

>
>Thanks!
>
>Eric Oldre
>
>On April 08, 2004 at 11:50:31, Robert Hyatt wrote:
>
>>On April 08, 2004 at 09:08:19, Andrew Wagner wrote:
>>
>>>Hi all,
>>>
>>>I'm using a simple hashing scheme: a single replace-always tranposition table.
>>>I've made sure all the hash keys are correct by comparing it to a key created
>>>from scratch. But I'm not sure it's working as efficiently as it could be. So,
>>>my question is: what statistics can I generate that will tell me how it's doing?
>>>And what values should I be getting for those statisics, on average?
>>>
>>>Also, a slightly different topic: someone told me that with hash tables, and
>>>without null-move, my move ordering (first-move fail-highs / total fail-highs)
>>>should be averaging >95%. Does that sound right to the rest of you? Thanks!
>>>Andrew
>>
>>
>>More like > 90%, with _some_ hitting >95%...



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