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Add setting to warn about copying/hashing large paths

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This is useful for diagnosing whether an evaluation is copying large
paths to the store. Example:

   $ nix build .#packages.x86_64-linux.default --large-path-warning-threshold 1000000
   warning: copied large path '/home/eelco/Dev/nix-master/' to the store (6271792 bytes)
   warning: copied large path '«github:NixOS/nixpkgs/b550fe4b4776908ac2a861124307045f8e717c8e?narHash=sha256-7kkJQd4rZ%2BvFrzWu8sTRtta5D1kBG0LSRYAfhtmMlSo%3D»/' to the store (155263768 bytes)
   warning: copied large path '«github:libgit2/libgit2/45fd9ed7ae1a9b74b957ef4f337bc3c8b3df01b5?narHash=sha256-oX4Z3S9WtJlwvj0uH9HlYcWv%2Bx1hqp8mhXl7HsLu2f0%3D»/' to the store (22175416 bytes)
   warning: copied large path '/nix/store/z985088mcd6w23qwdlirsinnyzayagki-source' to the store (5885872 bytes)
This commit is contained in:
Eelco Dolstra 2024-05-07 19:25:44 +02:00
parent d8559cad8d
commit dbe1b51580
9 changed files with 54 additions and 15 deletions
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20
src/libutil/serialise.hh
View file

@ -283,6 +283,26 @@ struct LengthSink : Sink
}
};
/**
* A wrapper source that counts the number of bytes read from it.
*/
struct LengthSource : Source
{
Source & next;
LengthSource(Source & next) : next(next)
{ }
uint64_t total = 0;
size_t read(char * data, size_t len) override
{
auto n = next.read(data, len);
total += n;
return n;
}
};
/**
* Convert a function into a sink.
*/