[Backport 2.32-maintenance] libexpr: Speed up BindingsBuilder::finishSizeIfNecessary#14372
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edolstra merged 1 commit into2.32-maintenancefrom Oct 27, 2025
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Instead of iterating over the newly built bindings we can do a cheaper set_intersection to count duplicates or fall back to a per-element binary search over the "base" bindings. This speeds up `hello` evaluation by around 10ms (0.196s -> 0.187s) and `nixos.closures.ec2.x86_64-linux` by 140ms (2.744s -> 2.609s). This addresses a somewhat steep performance regression from 82315c3 that reduced memory requirements of attribute set merges. With this patch we get back around to 2.31 level of eval performance while keeping the memory usage optimization. Also document the optimization a bit more. (cherry picked from commit ec2fd2d)
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Not sure if we should backport this, unless it's a fix to a major performance regression. |
Contributor
Generally it's a very safe change without any functional differences and the performance uplift will help a lot in nixpkgs CI. I think @wolfgangwalther and @philiptaron will agree that it's substantial enough that it warrants a backport. |
Contributor
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We can judge the impact on Nixpkgs CI within the week, but I'll leave it to the Nix team to decide if backporting is the right call. |
Contributor
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I can't comment on how safe the change is or not or whether it fully fixes the performance regression. But I can say that it would be very much appreciated to fix that regression in Nixpkgs quickly. I think that means I am 👍 on a backport ;) |
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Automatic backport to
2.32-maintenance, triggered by a label in #14362.