Previously, if the queue monitor thread encounters a build that Hydra has previously built, it downloaded the output paths from the binary cache, just to determine the build products and metrics. This is very inefficient. In particular, when doing something like merging nixpkgs:staging into nixpkgs:master, the queue monitor thread will be locked up for a long time fetching files from S3, causing the build farm to be mostly idle.
Of course this is entirely unnecessary, since the build products/metrics are already in the Hydra database. So now we just look up a previous build with the same output path, and copy the products/metrics.
WDGARQ76X6RLSFPJTW52BZYFKBC7DPSTABI7HHIKNYHBYXSUNTHQC ACBS7C6QGXAMPLQ336WAQMMGLZXBDNNYPE26ZBPUQ24GL4BF643AC BAFICF73XUYNAYT6T6X7GQIFHG6CLGPYYNFBMC6ON6SVPNOXO6RAC H7SZRHUBSEDJ3PQ3VOV4ZEEFUWTBPGZN53G6W26HHXPJDO7MSHJAC MHVIT4JYWUYD4UCGB2AHLXWLX6B5SYE22BREERNGANT7RGGDUFOAC VQISTKOPNAEUS2K2F73CMNNLGZATWUYIURD5CSVNBNF7Q5ZF4PXQC HJOEIMLRDVQ2KZI5HGL2HKGBM3AHP7YIKGKDAGFUNKRUXVRB24NAC DKJFD6JNNK5LJMRGQABMJZKMFZLGY3ADKJWF6J4BBHEUPY3NB67QC }}BuildOutput State::getBuildOutputCached(Connection & conn, nix::ref<nix::Store> destStore, const nix::Derivation & drv){{pqxx::work txn(conn);for (auto & output : drv.outputs) {auto r = txn.parameterized("select id, buildStatus, releaseName, closureSize, size from Builds b ""join BuildOutputs o on b.id = o.build ""where finished = 1 and (buildStatus = 0 or buildStatus = 6) and path = $1")(output.second.path).exec();if (r.empty()) continue;BuildID id = r[0][0].as<BuildID>();printMsg(lvlInfo, format("re-using products of build %d") % id);BuildOutput res;res.failed = r[0][1].as<int>() == bsFailedWithOutput;res.releaseName = r[0][2].is_null() ? "" : r[0][2].as<std::string>();res.closureSize = r[0][3].is_null() ? 0 : r[0][3].as<unsigned long long>();res.size = r[0][4].is_null() ? 0 : r[0][4].as<unsigned long long>();auto products = txn.parameterized("select type, subtype, fileSize, sha1hash, sha256hash, path, name, defaultPath from BuildProducts where build = $1 order by productnr")(id).exec();for (auto row : products) {BuildProduct product;product.type = row[0].as<std::string>();product.subtype = row[1].as<std::string>();if (row[2].is_null())product.isRegular = false;else {product.isRegular = true;product.fileSize = row[2].as<off_t>();}if (!row[3].is_null())product.sha1hash = parseHash(htSHA1, row[3].as<std::string>());if (!row[4].is_null())product.sha256hash = parseHash(htSHA256, row[4].as<std::string>());if (!row[5].is_null())product.path = row[5].as<std::string>();product.name = row[6].as<std::string>();if (!row[7].is_null())product.defaultPath = row[7].as<std::string>();res.products.emplace_back(product);}auto metrics = txn.parameterized("select name, unit, value from BuildMetrics where build = $1")(id).exec();for (auto row : metrics) {BuildMetric metric;metric.name = row[0].as<std::string>();metric.unit = row[1].is_null() ? "" : row[1].as<std::string>();metric.value = row[2].as<double>();res.metrics.emplace(metric.name, metric);}return res;