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* New command `nix-store --optimise' to reduce Nix store disk space

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usage by finding identical files in the store and hard-linking them
  to each other.  It typically reduces the size of the store by
  something like 25-35%.  This is what the optimise-store.pl script
  did, but the new command is faster and more correct (it's safe wrt
  garbage collection and concurrent builds).
This commit is contained in:
Eelco Dolstra 2007-10-09 22:14:27 +00:00
parent 27a0662828
commit a8629de827
5 changed files with 188 additions and 99 deletions
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91
scripts/optimise-store.pl
View file

@ -1,91 +0,0 @@
#! /usr/bin/perl -w
use strict;
use File::Basename;
my @paths = ("/nix/store");
print "hashing...\n";
my $hashList = "/tmp/nix-optimise-hash-list";
system("find @paths -type f -print0 | xargs -0 md5sum -- > $hashList") == 0
or die "cannot hash store files";
print "sorting by hash...\n";
system("sort $hashList > $hashList.sorted") == 0
or die "cannot sort list";
sub atomicLink {
my $target = shift;
my $new = shift;
my $tmpNew = "${new}_optimise.$$";
# Make the directory writable temporarily.
my $dir = dirname $new;
my @st = stat $dir or die;
chmod ($st[2] | 0200, $dir) or die "cannot make `$dir' writable: $!";
link $target, $tmpNew or die "cannot create hard link `$tmpNew': $!";
rename $tmpNew, $new or die "cannot rename `$tmpNew' to `$new': $!";
chmod ($st[2], $dir) or die "cannot restore permission on `$dir': $!";
utime ($st[8], $st[9], $dir) or die "cannot restore timestamp on `$dir': $!";
}
print "hard-linking...\n";
open LIST, "<$hashList.sorted" or die;
my $prevFile;
my $prevHash;
my $prevInode;
my $prevExec;
my $totalSpace = 0;
my $savedSpace = 0;
while (<LIST>) {
/^([0-9a-f]*)\s+(.*)$/ or die;
my $curFile = $2;
my $curHash = $1;
my @st = stat $curFile or die;
next if ($st[2] & 0222) != 0; # skip writable files
my $fileSize = $st[7];
$totalSpace += $fileSize;
my $isExec = ($st[2] & 0111) == 0111;
if (defined $prevHash && $curHash eq $prevHash
&& $prevExec == $isExec)
{
if ($st[1] != $prevInode) {
print "$curFile = $prevFile\n";
atomicLink $prevFile, $curFile;
$savedSpace += $fileSize;
}
} else {
$prevFile = $curFile;
$prevHash = $curHash;
$prevInode = $st[1];
$prevExec = ($st[2] & 0111) == 0111;
}
}
print "total space = $totalSpace\n";
print "saved space = $savedSpace\n";
my $savings = ($savedSpace / $totalSpace) * 100.0;
print "savings = $savings %\n";
close LIST;