From 4911a10a4e51102a21a5d123a852c75d2ec92dbc Mon Sep 17 00:00:00 2001
From: Eelco Dolstra <eelco.dolstra@logicblox.com>
Date: Fri, 29 Jun 2012 14:26:31 -0400
Subject: Use XZ compression in binary caches

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.
---
 corepkgs/config.nix.in | 3 ++-
 corepkgs/nar.nix       | 9 +++++----
 2 files changed, 7 insertions(+), 5 deletions(-)

(limited to 'corepkgs')

diff --git a/corepkgs/config.nix.in b/corepkgs/config.nix.in
index b324d732a1..1be4bd0904 100644
--- a/corepkgs/config.nix.in
+++ b/corepkgs/config.nix.in
@@ -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@";
diff --git a/corepkgs/nar.nix b/corepkgs/nar.nix
index 4747dc31de..c5155dcc91 100644
--- a/corepkgs/nar.nix
+++ b/corepkgs/nar.nix
@@ -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
-- 
cgit 1.4.1