Storage optimization: Difference between revisions

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The Nix store sometimes contains entries which are no longer useful.<ref group="cf.">[https://nixos.org/nix/manual/#sec-garbage-collection Nix Manual, 11. Garbage Collection]</ref> They can be deleted with {{ic|nix-collect-garbage -d}} <ref group="cf.">{{man|nix-collect-garbage|sec=1}}</ref> or {{ic|nix-store --gc}}.<ref group="cf.">{{man|nix-store|sec=1}}, under {{ic|OPERATION --GC}}</ref>

Note that if a result file still exists in the file system, all the dependencies used to build it will be kept. To see which result files prevent garbage collection, run:

Note that if a result file still exists in the file system, and your Nix configuration has both <code>keep-outputs = true</code> and <code>keep-derivations = true</code>, all the dependencies used to build it will be kept. To see which result files prevent garbage collection, run:

<syntaxhighlight lang="console">$ nix-store --gc --print-roots

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</syntaxhighlight>

Then you'll have a persistent environment which won't be garbage collected. This is useful when you don't want to spend time waiting for redownloads every time you enter the shell.

Then you'll have a persistent environment which won't be garbage collected as long as you have configured <code>keep-outputs = true</code>. This is useful when you don't want to spend time waiting for redownloads every time you enter the shell.

A little problem exists though. GC roots are numbered sequentially, so if you change <code>shell.nix</code> to contain '''fewer''' derivations, such that the name of the last GC root starts with <code>shell.drv-7</code>, then <code>shell.drv-{8,9,10,11,12}*</code> will be dangling and unused. To overcome this problem you should remove GC roots dir periodically (or just before running <code>nix-shell</code>).

@@ Line 17: / Line 17: @@
 The Nix store sometimes contains entries which are no longer useful.<ref group="cf.">[https://nixos.org/nix/manual/#sec-garbage-collection Nix Manual, 11. Garbage Collection]</ref> They can be deleted with {{ic|nix-collect-garbage -d}} <ref group="cf.">{{man|nix-collect-garbage|sec=1}}</ref> or {{ic|nix-store --gc}}.<ref group="cf.">{{man|nix-store|sec=1}}, under {{ic|OPERATION --GC}}</ref>
-Note that if a result file still exists in the file system, all the dependencies used to build it will be kept. To see which result files prevent garbage collection, run:
+Note that if a result file still exists in the file system, and your Nix configuration has both <code>keep-outputs = true</code> and <code>keep-derivations = true</code>, all the dependencies used to build it will be kept. To see which result files prevent garbage collection, run:
 <syntaxhighlight lang="console">$ nix-store --gc --print-roots
@@ Line 87: / Line 87: @@
 </syntaxhighlight>
-Then you'll have a persistent environment which won't be garbage collected. This is useful when you don't want to spend time waiting for redownloads every time you enter the shell.
+Then you'll have a persistent environment which won't be garbage collected as long as you have configured <code>keep-outputs = true</code>. This is useful when you don't want to spend time waiting for redownloads every time you enter the shell.
 A little problem exists though. GC roots are numbered sequentially, so if you change <code>shell.nix</code> to contain '''fewer''' derivations, such that the name of the last GC root starts with <code>shell.drv-7</code>, then <code>shell.drv-{8,9,10,11,12}*</code> will be dangling and unused. To overcome this problem you should remove GC roots dir periodically (or just before running <code>nix-shell</code>).