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While tinkering with a notebook that loads a large chunk of data in memory, I noticed that if I run it multiple times, the past chunks reside in memory. I understand that the reason (or one of) for which this happens is that the past output mechanism (%) keeps a reference to them, so they cannot be garbage collected.

Is there a way to explicitly make Mathematica forget some data?

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You can set $HistoryLength = 0 for instance. – b.gatessucks Nov 20 '12 at 12:03
related… – chris Nov 20 '12 at 13:17
Also related (or arguably duplicate)… – Jacob Akkerboom Mar 17 '13 at 18:59
up vote 4 down vote accepted


 $HistoryLength = k

to keep the last k lines of input and output.

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