diff --git a/src/hydra-queue-runner/Makefile.am b/src/hydra-queue-runner/Makefile.am
index 2525c936..00aa254d 100644
--- a/src/hydra-queue-runner/Makefile.am
+++ b/src/hydra-queue-runner/Makefile.am
@@ -1,6 +1,6 @@
 bin_PROGRAMS = hydra-queue-runner
 
-hydra_queue_runner_SOURCES = hydra-queue-runner.cc build-result.cc
+hydra_queue_runner_SOURCES = hydra-queue-runner.cc build-result.cc build-remote.cc
 hydra_queue_runner_LDADD = $(NIX_LIBS) -lpqxx
 
 AM_CXXFLAGS = $(NIX_CFLAGS) -Wall
diff --git a/src/hydra-queue-runner/build-remote.cc b/src/hydra-queue-runner/build-remote.cc
new file mode 100644
index 00000000..cbce20f3
--- /dev/null
+++ b/src/hydra-queue-runner/build-remote.cc
@@ -0,0 +1,170 @@
+#include <algorithm>
+
+#include <sys/types.h>
+#include <sys/stat.h>
+#include <fcntl.h>
+
+#include "build-remote.hh"
+
+#include "util.hh"
+#include "misc.hh"
+#include "serve-protocol.hh"
+#include "worker-protocol.hh"
+
+using namespace nix;
+
+
+struct Child
+{
+    Pid pid;
+    AutoCloseFD to, from;
+};
+
+
+static void openConnection(const string & sshName, const string & sshKey,
+    int stderrFD, Child & child)
+{
+    Pipe to, from;
+    to.create();
+    from.create();
+
+    child.pid = startProcess([&]() {
+
+        if (dup2(to.readSide, STDIN_FILENO) == -1)
+            throw SysError("cannot dup input pipe to stdin");
+
+        if (dup2(from.writeSide, STDOUT_FILENO) == -1)
+            throw SysError("cannot dup output pipe to stdout");
+
+        if (dup2(stderrFD, STDERR_FILENO) == -1)
+            throw SysError("cannot dup stderr");
+
+        Strings argv({"ssh", "-x", "-a", sshName, "--", "nix-store", "--serve", "--write"});
+
+        execvp("ssh", (char * *) stringsToCharPtrs(argv).data()); // FIXME: remove cast
+
+        throw SysError("cannot start ssh");
+    });
+
+    to.readSide.close();
+    from.writeSide.close();
+
+    child.to = to.writeSide.borrow();
+    child.from = from.readSide.borrow();
+}
+
+
+static void copyClosureTo(std::shared_ptr<StoreAPI> store,
+    FdSource & from, FdSink & to, const PathSet & paths,
+    bool useSubstitutes = false)
+{
+    PathSet closure;
+    for (auto & path : paths)
+        computeFSClosure(*store, path, closure);
+
+    Paths sorted = topoSortPaths(*store, closure);
+
+    /* Send the "query valid paths" command with the "lock" option
+       enabled. This prevents a race where the remote host
+       garbage-collect paths that are already there. Optionally, ask
+       the remote host to substitute missing paths. */
+    writeInt(cmdQueryValidPaths, to);
+    writeInt(1, to); // == lock paths
+    writeInt(useSubstitutes, to);
+    writeStrings(sorted, to);
+    to.flush();
+
+    /* Get back the set of paths that are already valid on the remote
+       host. */
+    auto present = readStorePaths<PathSet>(from);
+
+    PathSet missing;
+    std::set_difference(closure.begin(), closure.end(), present.begin(), present.end(),
+        std::inserter(missing, missing.end()));
+
+    printMsg(lvlError, format("sending %1% missing paths") % missing.size());
+    if (missing.empty()) return;
+
+    throw Error("NOT IMPL 1");
+}
+
+
+static void copyClosureFrom(std::shared_ptr<StoreAPI> store,
+    FdSource & from, FdSink & to, const PathSet & paths)
+{
+    writeInt(cmdExportPaths, to);
+    writeInt(0, to); // == don't sign
+    writeStrings(paths, to);
+    to.flush();
+    store->importPaths(false, from);
+}
+
+
+void buildRemote(std::shared_ptr<StoreAPI> store,
+    const string & sshName, const string & sshKey,
+    const Path & drvPath, const Derivation & drv,
+    const nix::Path & logDir, RemoteResult & result)
+{
+    string base = baseNameOf(drvPath);
+    Path logFile = logDir + "/" + string(base, 0, 2) + "/" + string(base, 2);
+
+    createDirs(dirOf(logFile));
+
+    AutoCloseFD logFD(open(logFile.c_str(), O_CREAT | O_TRUNC | O_WRONLY, 0666));
+    if (logFD == -1) throw SysError(format("creating log file ‘%1%’") % logFile);
+
+    Child child;
+    openConnection(sshName, sshKey, logFD, child);
+
+    logFD.close();
+
+    FdSource from(child.from);
+    FdSink to(child.to);
+
+    /* Handshake. */
+    writeInt(SERVE_MAGIC_1, to);
+    writeInt(SERVE_PROTOCOL_VERSION, to);
+    to.flush();
+
+    unsigned int magic = readInt(from);
+    if (magic != SERVE_MAGIC_2)
+        throw Error(format("protocol mismatch with ‘nix-store --serve’ on ‘%1%’") % sshName);
+    unsigned int version = readInt(from);
+    if (GET_PROTOCOL_MAJOR(version) != 0x200)
+        throw Error(format("unsupported ‘nix-store --serve’ protocol version on ‘%1%’") % sshName);
+
+    /* Copy the input closure. */
+    printMsg(lvlError, format("sending closure of ‘%1%’ to ‘%2%’") % drvPath % sshName);
+    copyClosureTo(store, from, to, PathSet({drvPath}));
+
+    /* Do the build. */
+    printMsg(lvlError, format("building ‘%1%’ on ‘%2%’") % drvPath % sshName);
+    writeInt(cmdBuildPaths, to);
+    writeStrings(PathSet({drvPath}), to);
+    writeInt(3600, to); // == maxSilentTime, FIXME
+    writeInt(7200, to); // == buildTimeout, FIXME
+    to.flush();
+    result.startTime = time(0);
+    int res = readInt(from);
+    result.stopTime = time(0);
+    if (res) {
+        result.errorMsg = (format("%1% on ‘%2%’") % readString(from) % sshName).str();
+        if (res == 100) result.status = RemoteResult::rrPermanentFailure;
+        else if (res == 101) result.status = RemoteResult::rrTimedOut;
+        else result.status = RemoteResult::rrMiscFailure;
+        return;
+    }
+
+    /* Copy the output paths. */
+    printMsg(lvlError, format("copying outputs of ‘%1%’ from ‘%2%’") % drvPath % sshName);
+    PathSet outputs;
+    for (auto & output : drv.outputs)
+        outputs.insert(output.second.path);
+    copyClosureFrom(store, from, to, outputs);
+
+    /* Shut down the connection. */
+    child.to.close();
+    child.pid.wait(true);
+
+    result.status = RemoteResult::rrSuccess;
+}
diff --git a/src/hydra-queue-runner/build-remote.hh b/src/hydra-queue-runner/build-remote.hh
new file mode 100644
index 00000000..6406bc58
--- /dev/null
+++ b/src/hydra-queue-runner/build-remote.hh
@@ -0,0 +1,21 @@
+#pragma once
+
+#include "store-api.hh"
+#include "derivations.hh"
+
+struct RemoteResult
+{
+    enum {
+        rrSuccess = 0,
+        rrPermanentFailure = 1,
+        rrTimedOut = 2,
+        rrMiscFailure = 3
+    } status = rrMiscFailure;
+    std::string errorMsg;
+    time_t startTime = 0, stopTime = 0;
+};
+
+void buildRemote(std::shared_ptr<nix::StoreAPI> store,
+    const std::string & sshName, const std::string & sshKey,
+    const nix::Path & drvPath, const nix::Derivation & drv,
+    const nix::Path & logDir, RemoteResult & result);
diff --git a/src/hydra-queue-runner/hydra-queue-runner.cc b/src/hydra-queue-runner/hydra-queue-runner.cc
index ada15e67..5fe9be2b 100644
--- a/src/hydra-queue-runner/hydra-queue-runner.cc
+++ b/src/hydra-queue-runner/hydra-queue-runner.cc
@@ -8,6 +8,7 @@
 #include <pqxx/pqxx>
 
 #include "build-result.hh"
+#include "build-remote.hh"
 #include "sync.hh"
 #include "pool.hh"
 
@@ -134,6 +135,10 @@ struct Step
 
     Sync<State> state;
 
+    std::atomic_bool destroyed;
+
+    Step() : destroyed(false) { }
+
     ~Step()
     {
         printMsg(lvlError, format("destroying step %1%") % drvPath);
@@ -141,11 +146,49 @@ struct Step
 };
 
 
+struct Machine
+{
+    typedef std::shared_ptr<Machine> ptr;
+
+    std::string sshName, sshKey;
+    std::set<std::string> systemTypes, supportedFeatures, mandatoryFeatures;
+    unsigned int maxJobs = 1;
+    float speedFactor = 1.0;
+
+    Sync<unsigned int> currentJobs;
+
+    Machine()
+    {
+        auto currentJobs_(currentJobs.lock());
+        *currentJobs_ = 0;
+    }
+};
+
+
+/* A RAII helper that manages the currentJobs field of Machine
+   objects. */
+struct MachineReservation
+{
+    typedef std::shared_ptr<MachineReservation> ptr;
+    Machine::ptr machine;
+    MachineReservation(Machine::ptr machine) : machine(machine)
+    {
+        auto currentJobs_(machine->currentJobs.lock());
+        (*currentJobs_)++;
+    }
+    ~MachineReservation()
+    {
+        auto currentJobs_(machine->currentJobs.lock());
+        if (*currentJobs_ > 0) (*currentJobs_)--;
+    }
+};
+
+
 class State
 {
 private:
 
-    std::thread queueMonitorThread;
+    Path hydraData, logDir;
 
     /* CV for waking up the queue. */
     std::condition_variable queueMonitorWakeup;
@@ -168,20 +211,35 @@ private:
 
     std::condition_variable_any runnableWakeup;
 
+    /* CV for waking up the dispatcher. */
+    std::condition_variable dispatcherWakeup;
+    std::mutex dispatcherMutex;
+
     /* PostgreSQL connection pool. */
     Pool<Connection> dbPool;
 
+    /* The build machines. */
+    typedef std::list<Machine::ptr> Machines;
+    Sync<Machines> machines;
+
+    /* The currently active builder threads. FIXME: We could re-use
+       these, but since they're fairly long-running, it's probably not
+       worth it. */
+    // std::vector<std::thread> builderThreads;
+
 public:
     State();
 
     ~State();
 
+    void loadMachines();
+
     void markActiveBuildStepsAsAborted(time_t stopTime);
 
     int createBuildStep(pqxx::work & txn, time_t startTime, Build::ptr build, Step::ptr step,
         BuildStepStatus status, const std::string & errorMsg = "", BuildID propagatedFrom = 0);
 
-    void finishBuildStep(pqxx::work & txn, time_t stopTime, BuildID buildId, int stepNr,
+    void finishBuildStep(pqxx::work & txn, time_t startTime, time_t stopTime, BuildID buildId, int stepNr,
         BuildStepStatus status, const string & errorMsg = "", BuildID propagatedFrom = 0);
 
     void updateBuild(pqxx::work & txn, Build::ptr build, BuildStatus status);
@@ -200,9 +258,17 @@ public:
 
     void makeRunnable(Step::ptr step);
 
-    void builderThreadEntry(int slot);
+    /* The thread that selects and starts runnable builds. */
+    void dispatcher();
 
-    void doBuildStep(std::shared_ptr<StoreAPI> store, Step::ptr step);
+    void wakeDispatcher();
+
+    MachineReservation::ptr findMachine(Step::ptr step);
+
+    void builder(Step::ptr step, MachineReservation::ptr reservation);
+
+    void doBuildStep(std::shared_ptr<StoreAPI> store, Step::ptr step,
+        Machine::ptr machine);
 
     void markSucceededBuild(pqxx::work & txn, Build::ptr build,
         const BuildResult & res, bool isCachedBuild, time_t startTime, time_t stopTime);
@@ -213,6 +279,10 @@ public:
 
 State::State()
 {
+    hydraData = getEnv("HYDRA_DATA");
+    if (hydraData == "") throw Error("$HYDRA_DATA must be set");
+
+    logDir = canonPath(hydraData + "/build-logs");
 }
 
 
@@ -227,6 +297,49 @@ State::~State()
 }
 
 
+void State::loadMachines()
+{
+    Path machinesFile = getEnv("NIX_REMOTE_SYSTEMS", "/etc/nix/machines");
+
+    Machines newMachines;
+
+    if (pathExists(machinesFile)) {
+
+        for (auto line : tokenizeString<Strings>(readFile(machinesFile), "\n")) {
+            line = trim(string(line, 0, line.find('#')));
+            auto tokens = tokenizeString<std::vector<std::string>>(line);
+            if (tokens.size() < 3) continue;
+            tokens.resize(7);
+
+            auto machine = std::make_shared<Machine>();
+            machine->sshName = tokens[0];
+            machine->systemTypes = tokenizeString<StringSet>(tokens[1], ",");
+            machine->sshKey = tokens[2];
+            if (tokens[3] != "")
+                string2Int(tokens[3], machine->maxJobs);
+            else
+                machine->maxJobs = 1;
+            machine->speedFactor = atof(tokens[4].c_str());
+            machine->supportedFeatures = tokenizeString<StringSet>(tokens[5], ",");
+            machine->mandatoryFeatures = tokenizeString<StringSet>(tokens[6], ",");
+            newMachines.push_back(machine);
+        }
+
+    } else {
+        auto machine = std::make_shared<Machine>();
+        machine->sshName = "localhost";
+        machine->systemTypes = StringSet({settings.thisSystem});
+        if (settings.thisSystem == "x86_64-linux")
+            machine->systemTypes.insert("i686-linux");
+        machine->maxJobs = settings.maxBuildJobs;
+        newMachines.push_back(machine);
+    }
+
+    auto machines_(machines.lock());
+    *machines_ = newMachines;
+}
+
+
 void State::markActiveBuildStepsAsAborted(time_t stopTime)
 {
     auto conn(dbPool.get());
@@ -262,15 +375,17 @@ int State::createBuildStep(pqxx::work & txn, time_t startTime, Build::ptr build,
 }
 
 
-void State::finishBuildStep(pqxx::work & txn, time_t stopTime, BuildID buildId, int stepNr,
+void State::finishBuildStep(pqxx::work & txn, time_t startTime, time_t stopTime, BuildID buildId, int stepNr,
     BuildStepStatus status, const std::string & errorMsg, BuildID propagatedFrom)
 {
+    assert(startTime);
+    assert(stopTime);
     txn.parameterized
-        ("update BuildSteps set busy = 0, status = $1, propagatedFrom = $4, errorMsg = $5, stopTime = $6 where build = $2 and stepnr = $3")
+        ("update BuildSteps set busy = 0, status = $1, propagatedFrom = $4, errorMsg = $5, startTime = $6, stopTime = $7 where build = $2 and stepnr = $3")
         ((int) status)(buildId)(stepNr)
         (propagatedFrom, propagatedFrom != 0)
         (errorMsg, errorMsg != "")
-        (stopTime, stopTime != 0).exec();
+        (startTime)(stopTime).exec();
 }
 
 
@@ -346,6 +461,7 @@ void State::getQueuedBuilds(std::shared_ptr<StoreAPI> store)
 
         if (!store->isValidPath(build->drvPath)) {
             /* Derivation has been GC'ed prematurely. */
+            printMsg(lvlInfo, format("aborting GC'ed build %1%") % build->id);
             pqxx::work txn(*conn);
             txn.parameterized
                 ("update Builds set finished = 1, buildStatus = $2, startTime = $3, stopTime = $3, errorMsg = $4 where id = $1")
@@ -366,6 +482,8 @@ void State::getQueuedBuilds(std::shared_ptr<StoreAPI> store)
             Derivation drv = readDerivation(build->drvPath);
             BuildResult res = getBuildResult(store, drv);
 
+            printMsg(lvlInfo, format("cached build %1%") % build->id);
+
             pqxx::work txn(*conn);
             time_t now = time(0);
             markSucceededBuild(txn, build, res, true, now, now);
@@ -385,6 +503,9 @@ void State::getQueuedBuilds(std::shared_ptr<StoreAPI> store)
             build->toplevel = step;
         }
 
+        printMsg(lvlInfo, format("added build %1% (top-level step %2%, %3% new runnable steps)")
+            % build->id % step->drvPath % newRunnable.size());
+
         /* Prior to this, the build is not visible to
            getDependentBuilds().  Now it is, so the build can be
            failed if a dependency fails. (It can't succeed right away
@@ -462,6 +583,9 @@ Step::ptr State::createStep(std::shared_ptr<StoreAPI> store, const Path & drvPat
 
 void State::destroyStep(Step::ptr step, bool proceed)
 {
+    if (step->destroyed) return;
+    step->destroyed = true;
+
     printMsg(lvlInfo, format("destroying build step ‘%1%’") % step->drvPath);
 
     {
@@ -547,6 +671,8 @@ std::set<Build::ptr> State::getDependentBuilds(Step::ptr step)
 
 void State::makeRunnable(Step::ptr step)
 {
+    printMsg(lvlInfo, format("step ‘%1%’ is now runnable") % step->drvPath);
+
     {
         auto step_(step->state.lock());
         assert(step_->deps.empty());
@@ -557,38 +683,109 @@ void State::makeRunnable(Step::ptr step)
         runnable_->push_back(step);
     }
 
-    runnableWakeup.notify_one();
+    wakeDispatcher();
 }
 
 
-void State::builderThreadEntry(int slot)
+void State::dispatcher()
 {
-    auto store = openStore(); // FIXME: pool
+    while (!exitRequested) {
+        printMsg(lvlError, "dispatcher woken up");
 
-    while (true)  {
-        /* Sleep until a runnable build step becomes available. */
-        Step::ptr step;
         {
             auto runnable_(runnable.lock());
-            while (runnable_->empty() && !exitRequested)
-                runnable_.wait(runnableWakeup);
-            if (exitRequested) break;
-            auto weak = *runnable_->begin();
-            runnable_->pop_front();
-            step = weak.lock();
-            if (!step) continue;
+            printMsg(lvlError, format("%1% runnable builds") % runnable_->size());
+
+            /* FIXME: we're holding the runnable lock too long
+               here. This could be more efficient. */
+
+            for (auto i = runnable_->begin(); i != runnable_->end(); ) {
+                auto step = i->lock();
+
+                /* Delete dead steps. */
+                if (!step) {
+                    i = runnable_->erase(i);
+                    continue;
+                }
+
+                auto reservation = findMachine(step);
+                if (!reservation) {
+                    printMsg(lvlError, format("cannot execute step ‘%1%’ right now") % step->drvPath);
+                    ++i;
+                    continue;
+                }
+
+                printMsg(lvlInfo, format("WOOHOO: starting step ‘%1%’ on machine ‘%2%’")
+                    % step->drvPath % reservation->machine->sshName);
+                i = runnable_->erase(i);
+
+                auto builderThread = std::thread(&State::builder, this, step, reservation);
+                builderThread.detach(); // FIXME?
+            }
         }
 
-        /* Build it. */
-        printMsg(lvlError, format("slot %1%: got build step ‘%2%’") % slot % step->drvPath);
-        doBuildStep(store, step);
+        /* Sleep until we're woken up (either because a runnable build
+           is added, or because a build finishes). */
+        {
+            std::unique_lock<std::mutex> lock(dispatcherMutex);
+            dispatcherWakeup.wait(lock);
+        }
     }
 
-    printMsg(lvlError, "builder thread exits");
+    printMsg(lvlError, "dispatcher exits");
 }
 
 
-void State::doBuildStep(std::shared_ptr<StoreAPI> store, Step::ptr step)
+void State::wakeDispatcher()
+{
+    { std::lock_guard<std::mutex> lock(dispatcherMutex); } // barrier
+    dispatcherWakeup.notify_all();
+}
+
+
+MachineReservation::ptr State::findMachine(Step::ptr step)
+{
+    auto machines_(machines.lock());
+
+    for (auto & machine : *machines_) {
+        if (!has(machine->systemTypes, step->drv.platform)) continue;
+        // FIXME: check features
+        {
+            auto currentJobs_(machine->currentJobs.lock());
+            if (*currentJobs_ >= machine->maxJobs) continue;
+        }
+        return std::make_shared<MachineReservation>(machine);
+    }
+
+    /* FIXME: distinguish between permanent failures (a matching
+       machine doesn't exist) and temporary failures (a matching
+       machine is not available). */
+
+    return 0;
+}
+
+
+void State::builder(Step::ptr step, MachineReservation::ptr reservation)
+{
+    try {
+        auto store = openStore(); // FIXME: pool
+        doBuildStep(store, step, reservation->machine);
+    } catch (std::exception & e) {
+        printMsg(lvlError, format("build thread for ‘%1%’: %2%") % step->drvPath % e.what());
+        // FIXME: put step back in runnable and retry
+    }
+
+    /* Release the machine and wake up the dispatcher. */
+    assert(reservation.unique());
+    reservation = 0;
+    wakeDispatcher();
+
+    printMsg(lvlError, "builder exits");
+}
+
+
+void State::doBuildStep(std::shared_ptr<StoreAPI> store, Step::ptr step,
+    Machine::ptr machine)
 {
     /* There can be any number of builds in the database that depend
        on this derivation. Arbitrarily pick one (though preferring a
@@ -625,27 +822,28 @@ void State::doBuildStep(std::shared_ptr<StoreAPI> store, Step::ptr step)
     /* Create a build step record indicating that we started
        building. */
     auto conn(dbPool.get());
-    time_t startTime = time(0);
+    RemoteResult result;
+    result.startTime = time(0);
     int stepNr;
     {
         pqxx::work txn(*conn);
-        stepNr = createBuildStep(txn, startTime, build, step, bssBusy);
+        stepNr = createBuildStep(txn, result.startTime, build, step, bssBusy);
         txn.commit();
     }
 
-    bool success = false;
-    std::string errorMsg;
     try {
-        store->buildPaths(PathSet({step->drvPath}));
-        success = true;
+        buildRemote(store, machine->sshName, machine->sshKey, step->drvPath, step->drv, logDir, result);
     } catch (Error & e) {
-        errorMsg = e.msg();
+        result.status = RemoteResult::rrMiscFailure;
+        result.errorMsg = e.msg();
+        printMsg(lvlError, format("ERROR: %1%") % e.msg());
+        abort();
     }
 
-    time_t stopTime = time(0);
+    if (!result.stopTime) result.stopTime = time(0);
 
     BuildResult res;
-    if (success) res = getBuildResult(store, step->drv);
+    if (result.status == RemoteResult::rrSuccess) res = getBuildResult(store, step->drv);
 
     // FIXME: handle failed-with-output
 
@@ -676,33 +874,34 @@ void State::doBuildStep(std::shared_ptr<StoreAPI> store, Step::ptr step)
     {
         pqxx::work txn(*conn);
 
-        if (success) {
+        if (result.status == RemoteResult::rrSuccess) {
 
-            finishBuildStep(txn, stopTime, build->id, stepNr, bssSuccess);
+            finishBuildStep(txn, result.startTime, result.stopTime, build->id, stepNr, bssSuccess);
 
             /* Mark all builds of which this derivation is the top
                level as succeeded. */
             for (auto build2 : direct)
-                markSucceededBuild(txn, build2, res, false, startTime, stopTime);
+                markSucceededBuild(txn, build2, res, false, result.startTime, result.stopTime);
 
         } else {
             /* Create failed build steps for every build that depends
                on this. */
-            finishBuildStep(txn, stopTime, build->id, stepNr, bssFailed, errorMsg);
+            finishBuildStep(txn, result.startTime, result.stopTime, build->id, stepNr, bssFailed, result.errorMsg);
 
             for (auto build2 : dependents) {
                 if (build == build2) continue;
-                createBuildStep(txn, stopTime, build2, step, bssFailed, errorMsg, build->id);
+                createBuildStep(txn, result.stopTime, build2, step, bssFailed, result.errorMsg, build->id);
             }
 
             /* Mark all builds that depend on this derivation as failed. */
             for (auto build2 : dependents) {
+                printMsg(lvlError, format("marking build %1% as failed") % build2->id);
                 txn.parameterized
                     ("update Builds set finished = 1, isCachedBuild = 0, buildStatus = $2, startTime = $3, stopTime = $4 where id = $1")
                     (build2->id)
                     ((int) (build2->drvPath == step->drvPath ? bsFailed : bsDepFailed))
-                    (startTime)
-                    (stopTime).exec();
+                    (result.startTime)
+                    (result.stopTime).exec();
                 build2->finishedInDB = true; // FIXME: txn might fail
             }
         }
@@ -715,7 +914,7 @@ void State::doBuildStep(std::shared_ptr<StoreAPI> store, Step::ptr step)
        dependent Build objects. Any Steps not referenced by other
        Builds will be destroyed as well. */
     for (auto build2 : dependents)
-        if (build2->toplevel == step || !success) {
+        if (build2->toplevel == step || result.status != RemoteResult::rrSuccess) {
             auto builds_(builds.lock());
             builds_->erase(build2->id);
         }
@@ -723,13 +922,15 @@ void State::doBuildStep(std::shared_ptr<StoreAPI> store, Step::ptr step)
     /* Remove the step from the graph. In case of success, make
        dependent build steps runnable if they have no other
        dependencies. */
-    destroyStep(step, success);
+    destroyStep(step, result.status == RemoteResult::rrSuccess);
 }
 
 
 void State::markSucceededBuild(pqxx::work & txn, Build::ptr build,
     const BuildResult & res, bool isCachedBuild, time_t startTime, time_t stopTime)
 {
+    printMsg(lvlError, format("marking build %1% as succeeded") % build->id);
+
     txn.parameterized
         ("update Builds set finished = 1, buildStatus = $2, startTime = $3, stopTime = $4, size = $5, closureSize = $6, releaseName = $7, isCachedBuild = $8 where id = $1")
         (build->id)
@@ -765,11 +966,11 @@ void State::run()
 {
     markActiveBuildStepsAsAborted(0);
 
-    queueMonitorThread = std::thread(&State::queueMonitor, this);
+    loadMachines();
 
-    std::vector<std::thread> builderThreads;
-    for (int n = 0; n < 4; n++)
-        builderThreads.push_back(std::thread(&State::builderThreadEntry, this, n));
+    auto queueMonitorThread = std::thread(&State::queueMonitor, this);
+
+    auto dispatcherThread = std::thread(&State::dispatcher, this);
 
     /* Wait for SIGINT. */
     {
@@ -785,9 +986,8 @@ void State::run()
     queueMonitorWakeup.notify_all();
     queueMonitorThread.join();
 
-    { auto runnable_(runnable.lock()); } // barrier
-    runnableWakeup.notify_all();
-    for (auto & thread : builderThreads) thread.join();
+    wakeDispatcher();
+    dispatcherThread.join();
 
     printMsg(lvlError, format("psql connections = %1%") % dbPool.count());
 }
diff --git a/src/lib/Hydra/Helper/Nix.pm b/src/lib/Hydra/Helper/Nix.pm
index 16d498fb..087e66cb 100644
--- a/src/lib/Hydra/Helper/Nix.pm
+++ b/src/lib/Hydra/Helper/Nix.pm
@@ -133,8 +133,9 @@ sub getDrvLogPath {
     my $base = basename $drvPath;
     my $bucketed = substr($base, 0, 2) . "/" . substr($base, 2);
     my $fn = ($ENV{NIX_LOG_DIR} || "/nix/var/log/nix") . "/drvs/";
-    for ($fn . $bucketed . ".bz2", $fn . $bucketed, $fn . $base . ".bz2", $fn . $base) {
-        return $_ if (-f $_);
+    my $fn2 = Hydra::Model::DB::getHydraPath . "/build-logs/";
+    for ($fn2 . $bucketed, $fn . $bucketed . ".bz2", $fn . $bucketed, $fn . $base . ".bz2", $fn . $base) {
+        return $_ if -f $_;
     }
     return undef;
 }