Quels objets groupés par classes occupent de la mémoire

jmap -histo <pid>

Exemple de résultat :

 num     #instances         #bytes  class name (module)
-------------------------------------------------------
   1:       1362240      282208168  [B (java.base@11.0.5)
   2:        951832      105719672  [C (java.base@11.0.5)
   3:       1062742       50457440  [Ljava.lang.String; (java.base@11.0.5)
   4:         31119       34863792  [I (java.base@11.0.5)
   5:       1070615       34259680  org.apache.cocoon.xml.SaxBuffer$StartElement
   6:       1296689       31120536  java.lang.String (java.base@11.0.5)
   7:        214401       28913920  [Ljava.lang.Object; (java.base@11.0.5)
   8:       1070740       25697760  org.xml.sax.helpers.AttributesImpl (java.xml@11.0.5)
   9:       1070615       25694760  org.apache.cocoon.xml.SaxBuffer$EndElement
  10:        578713       18518816  java.util.HashMap$Node (java.base@11.0.5)
  11:        916100       14657600  org.apache.cocoon.xml.SaxBuffer$Characters

Pour voir l'évolution :

jmap -histo 1234 > jmap-histo1.txt
# bcp plus tard
jmap -histo 1234 > jmap-histo2.txt
./compare-jmap-histo jmap-histo1.txt jmap-histo2.txt

avec le script

#!/usr/bin/perl
 
foreach (`cat $ARGV[0]`) {
	my ($instances, $sizes, $name) = /^\s*\d+:\s+(\d+)\s+(\d+)\s+(.*)/ or next;
	$prev{$name} = { sizes => $sizes, instances => $instances } if !$prev{$name}
}
foreach (`cat $ARGV[1]`) {
	my ($instances, $sizes, $name) = /^\s*\d+:\s+(\d+)\s+(\d+)\s+(.*)/ or next;
	my $prev = delete $prev{$name} or print("unknown prev $name\n"), next;
	printf "%4dM =>%4dM\t\t%7d => %7d\t%s\n", $prev->{sizes} / 1e6, $sizes / 1e6, $prev->{instances}, $instances, $name;
}