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Use XZ compression in binary caches

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XZ compresses significantly better than bzip2.  Here are the
compression ratios and execution times (using 4 cores in parallel) on
my /var/run/current-system (3.1 GiB):

  bzip2: total compressed size 849.56 MiB, 30.8% [2m08]
  xz -6: total compressed size 641.84 MiB, 23.4% [6m53]
  xz -7: total compressed size 621.82 MiB, 22.6% [7m19]
  xz -8: total compressed size 599.33 MiB, 21.8% [7m18]
  xz -9: total compressed size 588.18 MiB, 21.4% [7m40]

Note that compression takes much longer.  More importantly, however,
decompression is much faster:

  bzip2: 1m47.274s
  xz -6: 0m55.446s
  xz -7: 0m54.119s
  xz -8: 0m52.388s
  xz -9: 0m51.842s

The only downside to using -9 is that decompression takes a fair
amount (~65 MB) of memory.
This commit is contained in:
Eelco Dolstra 2012-06-29 14:26:31 -04:00
parent 49cd7387ad
commit 4911a10a4e
6 changed files with 24 additions and 19 deletions
Download patch file Download diff file Expand all files Collapse all files

3
corepkgs/config.nix.in
View file

@ -6,7 +6,8 @@ in {
perl = "@perl@";
shell = "@shell@";
coreutils = "@coreutils@";
bzip2 = fromEnv "NIX_BZIP2" "@bzip2@";
bzip2 = "@bzip2@";
xz = "@xz@";
tar = "@tar@";
tr = "@tr@";
nixBinDir = fromEnv "NIX_BIN_DIR" "@bindir@";

9
corepkgs/nar.nix
View file

@ -8,14 +8,15 @@ let
echo "packing ‘$storePath’..."
mkdir $out
dst=$out/tmp.nar.bz2
dst=$out/tmp.nar.xz
set -o pipefail
nix-store --dump "$storePath" | ${bzip2} > $dst
nix-store --dump "$storePath" | ${xz} -9 > $dst
nix-hash --flat --type $hashAlgo --base32 $dst > $out/narbz2-hash
hash=$(nix-hash --flat --type $hashAlgo --base32 $dst)
echo -n $hash > $out/nar-compressed-hash
mv $out/tmp.nar.bz2 $out/$(cat $out/narbz2-hash).nar.bz2
mv $dst $out/$hash.nar.xz
'';
in