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We need to distinguish explicitly between the paths used for the
scanner, and the paths that populate the derivation inputs. The full
paths must be accessible from the result of the refscanner to populate
drv fields correctly.
This was previously hidden by debug changes that masked actual IO
operations with no-ops.
Change-Id: I037af6e6bbe2b573034d695f8779bee1b56bc125
Reviewed-on: https://cl.tvl.fyi/c/depot/+/8022
Reviewed-by: flokli <flokli@flokli.de>
Tested-by: BuildkiteCI
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Switch out the string-scanning algorithm used in the reference scanner.
The construction of aho-corasick automata made up the vast majority of
runtime when evaluating nixpkgs previously. While the actual scanning
with a constructed automaton is relatively fast, we almost never scan
for the same set of strings twice and the cost is not worth it.
An algorithm that better matches our needs is the Wu-Manber multiple
string match algorithm, which works efficiently on *long* and *random*
strings of the *same length*, which describes store paths (up to their
hash component).
This switches the refscanner crate to a Rust implementation[0][1] of
this algorithm.
This has several implications:
1. This crate does not provide a way to scan streams. I'm not sure if
this is an inherent problem with the algorithm (probably not, but
it would need buffering). Either way, related functions and
tests (which were actually unused) have been removed.
2. All strings need to be of the same length. For this reason, we
truncate the known paths after their hash part (they are still
unique, of course).
3. Passing an empty set of matches, or a match that is shorter than
the length of a store path, causes the crate to panic. We safeguard
against this by completely skipping the refscanning if there are no
known paths (i.e. when evaluating the first derivation of an eval),
and by bailing out of scanning a string that is shorter than a
store path.
On the upside, this reduces overall runtime to less 1/5 of what it was
before when evaluating `pkgs.stdenv.drvPath`.
[0]: Frankly, it's a random, research-grade MIT-licensed
crate that I found on Github:
https://github.com/jneem/wu-manber
[1]: We probably want to rewrite or at least fork the above crate, and
add things like a three-byte wide scanner. Evaluating large
portions of nixpkgs can easily lead to more than 65k derivations
being scanned for.
Change-Id: I08926778e1e5d5a87fc9ac26e0437aed8bbd9eb0
Reviewed-on: https://cl.tvl.fyi/c/depot/+/8017
Tested-by: BuildkiteCI
Reviewed-by: flokli <flokli@flokli.de>
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No situation should be allowed in which a path is inserted into
known_paths with different types twice, which we previously enforced
only for some path types.
Change-Id: I8cb47d4b29c0aab3c58694f8b590e131deba7043
Reviewed-on: https://cl.tvl.fyi/c/depot/+/7843
Reviewed-by: flokli <flokli@flokli.de>
Tested-by: BuildkiteCI
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Replacement strings are some weird internal feature of Nix that is
required for calculating derivation hashes. We need to track these
like other paths, as they need to be re-used on builds with
dependencies on values from previous builds.
Change-Id: Ie955b3fb5ae3685cfadfbe4d06ea6b5e219590c7
Reviewed-on: https://cl.tvl.fyi/c/depot/+/7828
Reviewed-by: flokli <flokli@flokli.de>
Tested-by: BuildkiteCI
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When adding things to a C++ Nix store, ensure that the path is tracked
in the tracker.
Since the mechanism for propagating the tracker instance isn't
finalised yet, I've opted to take an Rc<RefCell> parameter for it. How
exactly that ends up there is going to become clear in the next
commits, but for now it's just instantiated in main with
Default::default.
Change-Id: I90f0b44f2d4f292dedc98ff1aa39041d279b61fd
Reviewed-on: https://cl.tvl.fyi/c/depot/+/7833
Tested-by: BuildkiteCI
Reviewed-by: flokli <flokli@flokli.de>
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This gets very complex very quickly otherwise, as all the construction
paths for a reference scanner and all the access patterns for the
KnownPaths structure are not yet fully understood.
Change-Id: Ibadf1f18b476695f3c286fc6896ae557760edf63
Reviewed-on: https://cl.tvl.fyi/c/depot/+/7827
Reviewed-by: flokli <flokli@flokli.de>
Tested-by: BuildkiteCI
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This module implements types used to track the set of known paths in
the context of an evaluation.
These are used to determine the build references of a derivation.
Change-Id: I81e15ae33632784e699128916485751613b231a3
Reviewed-on: https://cl.tvl.fyi/c/depot/+/7816
Tested-by: BuildkiteCI
Reviewed-by: flokli <flokli@flokli.de>
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