From abd858d3dcd8dbcb2ee2d17ff5b03dbce46821e7 Mon Sep 17 00:00:00 2001
From: Jack Kelly <jack.kelly@bellroy.com>
Date: Tue, 19 Dec 2023 07:54:40 +1000
Subject: [PATCH 1/2] Document the `store_uri` parameter by way of example

---
 doc/manual/src/configuration.md | 24 ++++++++++++++++++++++++
 1 file changed, 24 insertions(+)

diff --git a/doc/manual/src/configuration.md b/doc/manual/src/configuration.md
index 02210449..4954040c 100644
--- a/doc/manual/src/configuration.md
+++ b/doc/manual/src/configuration.md
@@ -74,6 +74,30 @@ following:
         }
     }
 
+Populating a Cache
+------------------
+
+A common use for Hydra is to pre-build and cache derivations which
+take a long time to build. While it is possible to direcly access the
+Hydra server's store over SSH, a more scalable option is to upload
+built derivations to a remote store like an [S3-compatible object
+store](https://nixos.org/manual/nix/stable/command-ref/new-cli/nix3-help-stores.html#s3-binary-cache-store). Setting
+the `store_uri` parameter will cause Hydra to sign and upload
+derivations as they are built:
+
+```
+store_uri = s3://cache-bucket-name?compression=zstd&parallel-compression=true&write-nar-listing=1&ls-compression=br&log-compression=br&secret-key=/path/to/cache/private/key
+```
+
+This example uses [Zstandard](https://github.com/facebook/zstd)
+compression on derivations to reduce CPU usage on the server, but
+[Brotli](https://brotli.org/) compression for derivation listings and
+build logs because it has better browser support.
+
+See [`nix help
+stores`](https://nixos.org/manual/nix/stable/command-ref/new-cli/nix3-help-stores.html)
+for a description of the store URI format.
+
 Statsd Configuration
 --------------------
 

From 75f26f1fc4f114b7f930c57ba37212ea67990de1 Mon Sep 17 00:00:00 2001
From: John Ericson <John.Ericson@Obsidian.Systems>
Date: Sat, 23 Dec 2023 19:10:58 -0500
Subject: [PATCH 2/2] Clean up `std::optional` dereferencing in the queue
 runner

Instead of doing this partial operation a number of times, assert (with
a comment, get a reference to the thing inside, and use that just once.
(This refactor was done twice, "just once" for each time.)
---
 src/hydra-queue-runner/queue-monitor.cc | 26 ++++++++++++++-----------
 1 file changed, 15 insertions(+), 11 deletions(-)

diff --git a/src/hydra-queue-runner/queue-monitor.cc b/src/hydra-queue-runner/queue-monitor.cc
index 6c339af6..09a2871e 100644
--- a/src/hydra-queue-runner/queue-monitor.cc
+++ b/src/hydra-queue-runner/queue-monitor.cc
@@ -495,12 +495,14 @@ Step::ptr State::createStep(ref<Store> destStore,
 
         size_t avail = 0;
         for (auto & i : missing) {
-            auto path = i.second.path(*localStore, step->drv->name, i.first);
-            if (/* localStore != destStore && */ localStore->isValidPath(*path))
+            auto pathOpt = i.second.path(*localStore, step->drv->name, i.first);
+            assert(pathOpt); // CA derivations not yet supported
+            auto & path = *pathOpt;
+            if (/* localStore != destStore && */ localStore->isValidPath(path))
                 avail++;
             else if (useSubstitutes) {
                 SubstitutablePathInfos infos;
-                localStore->querySubstitutablePathInfos({{*path, {}}}, infos);
+                localStore->querySubstitutablePathInfos({{path, {}}}, infos);
                 if (infos.size() == 1)
                     avail++;
             }
@@ -509,25 +511,27 @@ Step::ptr State::createStep(ref<Store> destStore,
         if (missing.size() == avail) {
             valid = true;
             for (auto & i : missing) {
-                auto path = i.second.path(*localStore, step->drv->name, i.first);
+                auto pathOpt = i.second.path(*localStore, step->drv->name, i.first);
+                assert(pathOpt); // CA derivations not yet supported
+                auto & path = *pathOpt;
 
                 try {
                     time_t startTime = time(0);
 
-                    if (localStore->isValidPath(*path))
+                    if (localStore->isValidPath(path))
                         printInfo("copying output ‘%1%’ of ‘%2%’ from local store",
-                            localStore->printStorePath(*path),
+                            localStore->printStorePath(path),
                             localStore->printStorePath(drvPath));
                     else {
                         printInfo("substituting output ‘%1%’ of ‘%2%’",
-                            localStore->printStorePath(*path),
+                            localStore->printStorePath(path),
                             localStore->printStorePath(drvPath));
-                        localStore->ensurePath(*path);
+                        localStore->ensurePath(path);
                         // FIXME: should copy directly from substituter to destStore.
                     }
 
                     copyClosure(*localStore, *destStore,
-                        StorePathSet { *path },
+                        StorePathSet { path },
                         NoRepair, CheckSigs, NoSubstitute);
 
                     time_t stopTime = time(0);
@@ -535,13 +539,13 @@ Step::ptr State::createStep(ref<Store> destStore,
                     {
                         auto mc = startDbUpdate();
                         pqxx::work txn(conn);
-                        createSubstitutionStep(txn, startTime, stopTime, build, drvPath, "out", *path);
+                        createSubstitutionStep(txn, startTime, stopTime, build, drvPath, "out", path);
                         txn.commit();
                     }
 
                 } catch (Error & e) {
                     printError("while copying/substituting output ‘%s’ of ‘%s’: %s",
-                        localStore->printStorePath(*path),
+                        localStore->printStorePath(path),
                         localStore->printStorePath(drvPath),
                         e.what());
                     valid = false;