Answers.Body: <p>Yes, Stockfish will go deeper if the hash is large enough to make a difference. The default value is 16 MB which is not a lot. After increasing the hash you likely see that the second time the search depth reached after 500 ms is higher than the first time you let Stockfish calculate.</p>
  <pre><code>setoption name Hash value 256
  </code></pre>
  
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Answers.Text: Thank you for your answer. By now, I also observed that when I called the Stockfish engine multiple times on the same position, the analysis depth increased - meaning Stockfish remembered earlier analysis results and built on those to improve the analysis.
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Answers.Body: <p>One UCI session you mean? To make reproducible experiments or test above, you can compare/contrast multiple calls, by using the UCI purge hash.</p>
  <p>&quot;setoption name Clear Hash&quot;</p>
  
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Body: <p>Let's say I call Stockfish via</p>
  <pre><code>&gt; position fen rnbqkbnr/pppppppp/8/8/8/8/PPPPPPPP/RNBQKBNR w KQkq - 0 1
  &gt;'go movetime 500';
  </code></pre>
  <p>Now, after Stockfish has finished the analysis, what happens if I call stockfish again with the same position?</p>
  <pre><code>&gt; position fen rnbqkbnr/pppppppp/8/8/8/8/PPPPPPPP/RNBQKBNR w KQkq - 0 1
  &gt; go movetime 500
  </code></pre>
  <p>Will Stockfish build on the already performed analysis and simply go deeper? Or will it start the analysis anew?</p>
  
Tags: <engines>
Title: Does chess engine Stockfish remember already performed calculations within one session?
ThreadText: # Does chess engine Stockfish remember already performed calculations within one session?
  
  (Asked by: username_0 on 2023-12-20)
  
  Let's say I call Stockfish via
  
  ```
  > position fen rnbqkbnr/pppppppp/8/8/8/8/PPPPPPPP/RNBQKBNR w KQkq - 0 1
  >'go movetime 500';
  
  ```
  
  Now, after Stockfish has finished the analysis, what happens if I call stockfish again with the same position?
  
  ```
  > position fen rnbqkbnr/pppppppp/8/8/8/8/PPPPPPPP/RNBQKBNR w KQkq - 0 1
  > go movetime 500
  
  ```
  
  Will Stockfish build on the already performed analysis and simply go deeper? Or will it start the analysis anew?
  
  **Tags:** engines
  
  
  ---
  
  ## 2 answers
  
  ### Answer by username_1 on 2023-12-20. Score: 5 | Accepted answer
  
  Yes, Stockfish will go deeper if the hash is large enough to make a difference. The default value is 16 MB which is not a lot. After increasing the hash you likely see that the second time the search depth reached after 500 ms is higher than the first time you let Stockfish calculate.
  
  ```
  setoption name Hash value 256
  
  ```
  
  > **Comments:**
  > **username_0**: Thank you for your answer. By now, I also observed that when I called the Stockfish engine multiple times on the same position, the analysis depth increased - meaning Stockfish remembered earlier analysis results and built on those to improve the analysis.  
  
  ---
  
  ### Answer by username_2 on 2023-12-22. Score: 2
  
  One UCI session you mean? To make reproducible experiments or test above, you can compare/contrast multiple calls, by using the UCI purge hash.
  
  "setoption name Clear Hash"
  
  
  ---
  
  