forked from lix-project/lix
11800e6198
Getting substitute information using the binary cache substituter has non-trivial latency overhead. A package or NixOS system configuration can have hundreds of dependencies, and in the worst case (when the local info cache is empty) we have to do a separate HTTP request for each of these. If the ping time to the server is t, getting N info files will take tN seconds; e.g., with a ping time of 0.1s to nixos.org, sequentially downloading 1000 info files (a typical NixOS config) will take at least 100 seconds. To fix this problem, the binary cache substituter can now perform requests in parallel. This required changing the substituter interface to support a function querySubstitutablePathInfos() that queries multiple paths at the same time, and rewriting queryMissing() to take advantage of parallelism. (Due to local caching, parallelising queryMissing() is sufficient for most use cases, since it's almost always called before building a derivation and thus fills the local info cache.) For example, parallelism speeds up querying all 1056 paths in a particular NixOS system configuration from 116s to 2.6s. It works so well because the eccentricity of the top-level derivation in the dependency graph is only 9. So we only need 10 round-trips (when using an unlimited number of parallel connections) to get everything. Currently we do a maximum of 150 parallel connections to the server. Thus it's important that the binary cache server (e.g. nixos.org) has a high connection limit. Alternatively we could use HTTP pipelining, but WWW::Curl doesn't support it and libcurl has a hard-coded limit of 5 requests per pipeline. |
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| .. | ||
| build.cc | ||
| derivations.cc | ||
| derivations.hh | ||
| gc.cc | ||
| globals.cc | ||
| globals.hh | ||
| local-store.cc | ||
| local-store.hh | ||
| Makefile.am | ||
| misc.cc | ||
| misc.hh | ||
| optimise-store.cc | ||
| pathlocks.cc | ||
| pathlocks.hh | ||
| references.cc | ||
| references.hh | ||
| remote-store.cc | ||
| remote-store.hh | ||
| schema.sql | ||
| store-api.cc | ||
| store-api.hh | ||
| worker-protocol.hh | ||