https://issues.apache.org/SpamAssassin/show_bug.cgi?id=6514
Summary: More carefully distinguish between perl clearing and
deallocating memory
Product: Spamassassin
Version: SVN Trunk (Latest Devel Version)
Platform: All
OS/Version: All
Status: NEW
Severity: enhancement
Priority: P2
Component: Libraries
AssignedTo: [email protected]
ReportedBy: [email protected]
SpamAssassin is quite memory hungry for various reasons. Its basic premise
is that a complete mail message is available in memory, and often in several
representations. Due to the way Perl allocates/reuses memory, when a
long-running process (such as spamd or amavisd) is processing more than
one message in a row, its memory footprint often grows, and cannot shrink.
It would be difficult to change that approach, but at least we can help
perl's memory management a little when an application knows something
which perl by itself can not.
Here is a most instructive insight into perl memory management,
explaining a distinction between clearing and deallocating memory:
http://www.perlmonks.org/?node_id=803515
In brief:
my $a = "abc"; $a = ""; # clears but leaves buffer allocated
my $a = "abc"; $a = undef; # clears but leaves buffer allocated
my $a = "abc"; undef $a; # deallocates buffer
{ my $a = "abc"; ... }; # getting out of scope does not deallocate
and similarly for arrays and hashes:
my @a = (1,2,3); @a = (); # clears but leaves array allocated
my @a = (1,2,3); undef @a; # deallocates array
Whether clearing or deallocating is more appropriate depends on
what is a future expected use of such a variable, and how big it is.
Clearing is fast, deallocating makes memory available for other uses
but burdens memory management more.
I'm opening this ticket just as a general reminder and a placeholder
for comments. I may tweak some detail in this regard when I stumble
across it.
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