[isabelle-dev] NEWS: significantly reduced ML heap usage

Makarius makarius at sketis.net
Tue May 30 12:14:34 CEST 2023

*** General ***

* ML heap usage and stored heap size has been significantly reduced,
especially for applications with a lot of definitions in a 'locale' or
'class' context. The shrink factor is usually in the range 1.1 .. 2.0,
but a factor 3 .. 10 has been seen in unusual situations. This often
allows big applications to return to the "small" 64_32 memory model with
its hard limit of 16 GiB, and thus reduce the heap size by another
factor 1.8.

This refers to current f3d19c8445ec: many changesets are leading towards this 
great improvement. The key point is actually rather small:

changeset:   78048:f16067da45ef
user:        wenzelm
date:        Mon May 15 14:13:58 2023 +0200
files:       src/Pure/Isar/proof_context.ML src/Pure/assumption.ML 
avoid capture of inner/outer context and thus reduce heaps sizes by 20..40% 
(see also dd04a8b654fc, e49bf4ebf330, 9c19e15c8548, 71467e35fc3c);

That factor 1.2 .. 1.4 was merely for HOL and HOL-Analysis. Better factors are 
seen here:

   HOL-Algebra  3.6
   HOL-Probability 1.6

   Category3  5.2
   MonoidalCategory   7.6


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