Russell Sherwood Sunday, April 22, 2018
Note: It's amazing the pictures you get searching for Hash!
I've been asked this question by a number of people recently so an explanation of Hash files and their interactions with Engines is probably overdue.
Hash Files (Also known as Transposition Tables) are a tool utilised by Engines to facilitate the use of multiple processors. In very simple terms when we run an engine with multiple cores, rather than all the cores working on one position, there are actually single cores working on multiple nodes. These nodes start to make up a map of all of the moves which emanate from the start position.
In practice, the larger these tables are the better and a "rule of thumb" is to set them to around 50% of the RAM on the computer.
An advanced use is the saving of Hashtables. If deep searching is your thing then this allows you to save your analysis and reload it at a later date and return very quickly to the same depth.
Almost all major engines allow this use of HashTables. Stockfish 9 is the exception, although almost every Stockfish variant does have this functionality! So how do we do this?
(I'm using Houdini and Chessbase as an example, the method is more or less the same for all others)
1) Create a Folder where you are going to store the Hash File. Remeber that each of these files will be probably be Gigabytes in size so you need plenty of spare space on your drive.
2) Decide on the naming format you will use for these files. It could be the ICCF Game Number or whatever you want.
3) Double Click on the Engine Name in the Engine Window
4) Click "Advanced" in the Load Engine Window
5) Click "Engine Parameters"
6) Enter the File and Location for the Hash file in the "Hash file" Window - For example it could be C:\Hash\Test1
7) Select "Never Clear Hash"
8) Click OK
9) Run your Analysis and then click the Stop Icon
10) When you want to save Follow Steps 3-4-5 then Click "Save Hash to File"
11) When it has saved you will be able to Click OK, OK, OK to return to the front screen.
12) When you want to reload this file you simply follow steps 3-4-5, change the file to the name you want to load and click " Load Hash From File"
13) When the Load is finished, click OK, OK, OK and you are good to go.
When you have made your move you do not need to automatically create a new file but if you either (a) Don't follow the principle variation or (b) Move further away from the original position the effectiveness of the process reduces dramatically!