Add a minimum age gate option to the nix-collect-garbage / nix store gc commands

doc/manual/rl-next/gc-age-gate.md

@@ -0,0 +1,22 @@
+---
+synopsis: "Store GCs can now be restricted with a minimum age"
+prs: [14725]
+issues: [7572]
+---
+
+Nix store GCs invoked using either `nix-collect-garbage` or `nix store gc` may
+now be restricted to only deleting paths older than a certain minimum age, i.e.
+whose most recent usage is more than *n* days in the past. "Usage" is
+intentionally defined ambiguously, however in general all operations which
+produce/require the presence of a given store path count as "usage".
+
+
+Example usage:
+
+```bash
+# Delete store paths older than 7 days
+nix store gc --older-than 7d
+
+# Alternatively:
+nix-collect-garbage --path-older-than 7d
+```

doc/manual/source/command-ref/nix-collect-garbage.md

@@ -4,7 +4,7 @@
 
 # Synopsis
 
-`nix-collect-garbage` [`--delete-old`] [`-d`] [`--delete-older-than` *period*] [`--max-freed` *bytes*] [`--dry-run`]
+`nix-collect-garbage` [`--delete-old`] [`-d`] [`--delete-older-than` *period*] [`--delete-paths-older-than` *period*] [`--max-freed` *bytes*] [`--dry-run`]
 
 # Description
 
@@ -62,7 +62,17 @@ These options are for deleting old [profiles] prior to deleting unreachable [sto
   This is the equivalent of invoking [`nix-env --delete-generations <period>`](@docroot@/command-ref/nix-env/delete-generations.md#generations-time) on each found profile.
   See the documentation of that command for additional information about the *period* argument.
 
-  - <span id="opt-max-freed">[`--max-freed`](#opt-max-freed)</span> *bytes*
+- <span id="opt-paths-delete-older-than">[`--delete-paths-older-than`](#opt-delete-paths-older-than)</span> *period*
+
+  Only delete store paths older than the specified amount, i.e. restrict the GC
+  to only deleting store paths whose most recent usage is more than *N* days in
+  the past. *period* is a value such as `30d`, which would mean 30 days.
+
+  "Usage" is intentionally defined ambiguously, however in general all
+  operations which produce/require the presence of a given store path count as
+  "usage".
+
+- <span id="opt-max-freed">[`--max-freed`](#opt-max-freed)</span> *bytes*
 
 <!-- duplication from https://github.com/NixOS/nix/blob/442a2623e48357ff72c77bb11cf2cf06d94d2f90/doc/manual/source/command-ref/nix-store/gc.md?plain=1#L39-L44 -->
 

doc/manual/source/protocols/json/schema/store-object-info-v2.yaml

@@ -118,6 +118,7 @@ $defs:
       # impure
       - deriver
       - registrationTime
+      - lastUsageTime
       - ultimate
       - signatures
     properties:
@@ -147,6 +148,15 @@ $defs:
 
           > This is an "impure" field that may not be included in certain contexts.
 
+      lastUsageTime:
+        type: ["integer", "null"]
+        title: Last Usage Time
+        description: |
+          If known, when this derivation was last used (Unix timestamp).
+          Otherwise `null`.
+
+          > This is an "impure" field that may not be included in certain contexts.
+
       ultimate:
         type: boolean
         title: Ultimate
@@ -195,6 +205,7 @@ $defs:
       # impure
       - deriver
       - registrationTime
+      - lastUsageTime
       - ultimate
       - signatures
       # nar
@@ -211,6 +222,7 @@ $defs:
       ca: { $ref: "#/$defs/base/properties/ca" }
       deriver: { $ref: "#/$defs/impure/properties/deriver" }
       registrationTime: { $ref: "#/$defs/impure/properties/registrationTime" }
+      lastUsageTime: { $ref: "#/$defs/impure/properties/lastUsageTime" }
       ultimate: { $ref: "#/$defs/impure/properties/ultimate" }
       signatures: { $ref: "#/$defs/impure/properties/signatures" }
       closureSize: { $ref: "#/$defs/impure/properties/closureSize" }

src/libexpr/primops.cc

@@ -1936,6 +1936,8 @@ static void prim_storePath(EvalState & state, const PosIdx pos, Value ** args, V
     auto path2 = state.store->toStorePath(path.abs()).first;
     if (!settings.readOnlyMode)
         state.store->ensurePath(path2);
+    else
+        state.store->bumpLastUsageTime(path2);
     context.insert(NixStringContextElem::Opaque{.path = path2});
     v.mkString(path.abs(), context, state.mem);
 }

src/libexpr/primops/context.cc

@@ -273,6 +273,8 @@ static void prim_appendContext(EvalState & state, const PosIdx pos, Value ** arg
         auto namePath = state.store->parseStorePath(name);
         if (!settings.readOnlyMode)
             state.store->ensurePath(namePath);
+        else
+            state.store->bumpLastUsageTime(namePath);
         state.forceAttrs(*i.value, i.pos, "while evaluating the value of a string context");
 
         if (auto attr = i.value->attrs()->get(sPath)) {

src/libstore-tests/data/dummy-store/one-flat-file.json

@@ -28,6 +28,7 @@
         "narSize": 120,
         "references": [],
         "registrationTime": null,
+        "lastUsageTime": null,
         "signatures": [],
         "ultimate": false,
         "version": 2

src/libstore-tests/data/nar-info/json-1/impure.json

@@ -11,6 +11,7 @@
     "/nix/store/n5wkd9frr45pa74if5gpz9j7mifg27fh-foo"
   ],
   "registrationTime": 23423,
+  "lastUsageTime": 34534,
   "signatures": [
     "asdf",
     "qwer"

src/libstore-tests/data/nar-info/json-2/impure.json

@@ -26,6 +26,7 @@
     "n5wkd9frr45pa74if5gpz9j7mifg27fh-foo"
   ],
   "registrationTime": 23423,
+  "lastUsageTime": 34534,
   "signatures": [
     "asdf",
     "qwer"

src/libstore-tests/data/path-info/json-1/empty_impure.json

@@ -5,6 +5,7 @@
   "narSize": 0,
   "references": [],
   "registrationTime": null,
+  "lastUsageTime": null,
   "signatures": [],
   "ultimate": false,
   "version": 1

src/libstore-tests/data/path-info/json-1/impure.json

@@ -8,6 +8,7 @@
     "/nix/store/n5wkd9frr45pa74if5gpz9j7mifg27fh-foo"
   ],
   "registrationTime": 23423,
+  "lastUsageTime": 34534,
   "signatures": [
     "asdf",
     "qwer"

src/libstore-tests/data/path-info/json-2/empty_impure.json

@@ -9,6 +9,7 @@
   "narSize": 0,
   "references": [],
   "registrationTime": null,
+  "lastUsageTime": null,
   "signatures": [],
   "ultimate": false,
   "version": 2

src/libstore-tests/data/path-info/json-2/impure.json

@@ -19,6 +19,7 @@
     "n5wkd9frr45pa74if5gpz9j7mifg27fh-foo"
   ],
   "registrationTime": 23423,
+  "lastUsageTime": 34534,
   "signatures": [
     "asdf",
     "qwer"

src/libstore-tests/data/serve-protocol/unkeyed-valid-path-info-2.3.json

@@ -10,6 +10,7 @@
     "narSize": 34878,
     "references": [],
     "registrationTime": null,
+    "lastUsageTime": null,
     "signatures": [],
     "ultimate": false,
     "version": 2
@@ -27,6 +28,7 @@
       "g1w7hyyyy1w7hy3qg1w7hy3qgqqqqy3q-foo.drv"
     ],
     "registrationTime": null,
+    "lastUsageTime": null,
     "signatures": [],
     "ultimate": false,
     "version": 2

src/libstore-tests/data/serve-protocol/unkeyed-valid-path-info-2.4.json

@@ -12,6 +12,7 @@
       "g1w7hyyyy1w7hy3qg1w7hy3qgqqqqy3q-foo.drv"
     ],
     "registrationTime": null,
+    "lastUsageTime": null,
     "signatures": [],
     "ultimate": false,
     "version": 2
@@ -37,6 +38,7 @@
       "n5wkd9frr45pa74if5gpz9j7mifg27fh-foo"
     ],
     "registrationTime": null,
+    "lastUsageTime": null,
     "signatures": [
       "fake-sig-1",
       "fake-sig-2"

src/libstore-tests/data/worker-protocol/unkeyed-valid-path-info-1.15.json

@@ -10,6 +10,7 @@
     "narSize": 34878,
     "references": [],
     "registrationTime": 23423,
+    "lastUsageTime": null,
     "signatures": [],
     "ultimate": false,
     "version": 2
@@ -27,6 +28,7 @@
       "g1w7hyyyy1w7hy3qg1w7hy3qgqqqqy3q-foo.drv"
     ],
     "registrationTime": 23423,
+    "lastUsageTime": null,
     "signatures": [],
     "ultimate": false,
     "version": 2

src/libstore-tests/data/worker-protocol/valid-path-info-1.15.json

@@ -11,6 +11,7 @@
     "path": "g1w7hy3qg1w7hy3qg1w7hy3qg1w7hy3q-bar",
     "references": [],
     "registrationTime": 23423,
+    "lastUsageTime": null,
     "signatures": [],
     "ultimate": false,
     "version": 2
@@ -30,6 +31,7 @@
       "g1w7hyyyy1w7hy3qg1w7hy3qgqqqqy3q-foo"
     ],
     "registrationTime": 23423,
+    "lastUsageTime": null,
     "signatures": [],
     "ultimate": false,
     "version": 2

src/libstore-tests/data/worker-protocol/valid-path-info-1.16.json

@@ -11,6 +11,7 @@
     "path": "g1w7hy3qg1w7hy3qg1w7hy3qg1w7hy3q-bar",
     "references": [],
     "registrationTime": 23423,
+    "lastUsageTime": null,
     "signatures": [],
     "ultimate": true,
     "version": 2
@@ -30,6 +31,7 @@
       "g1w7hyyyy1w7hy3qg1w7hy3qgqqqqy3q-foo"
     ],
     "registrationTime": 23423,
+    "lastUsageTime": null,
     "signatures": [
       "fake-sig-1",
       "fake-sig-2"
@@ -59,6 +61,7 @@
       "n5wkd9frr45pa74if5gpz9j7mifg27fh-foo"
     ],
     "registrationTime": 23423,
+    "lastUsageTime": null,
     "signatures": [],
     "ultimate": false,
     "version": 2

src/libstore-tests/nar-info.cc

@@ -58,6 +58,7 @@ static NarInfo makeNarInfo(const Store & store, bool includeImpureInfo)
             "g1w7hy3qg1w7hy3qg1w7hy3qg1w7hy3q-bar.drv",
         };
         info.registrationTime = 23423;
+        info.lastUsageTime = 34534;
         info.ultimate = true;
         info.sigs = {"asdf", "qwer"};
 

src/libstore-tests/path-info.cc

@@ -64,6 +64,7 @@ static ValidPathInfo makeFullKeyed(const Store & store, bool includeImpureInfo)
             "g1w7hy3qg1w7hy3qg1w7hy3qg1w7hy3q-bar.drv",
         };
         info.registrationTime = 23423;
+        info.lastUsageTime = 34534;
         info.ultimate = true;
         info.sigs = {"asdf", "qwer"};
     }

src/libstore/binary-cache-store.cc

@@ -295,6 +295,7 @@ void BinaryCacheStore::addToStore(
 {
     if (!repair && isValidPath(info.path)) {
         // FIXME: copyNAR -> null sink
+        bumpLastUsageTime(info.path);
         narSource.drain();
         return;
     }

src/libstore/build/derivation-building-goal.cc

@@ -117,8 +117,10 @@ Goal::Co DerivationBuildingGoal::gaveUpOnSubstitution(bool storeDerivation)
     }
 
     for (auto & i : drv->inputSrcs) {
-        if (worker.store.isValidPath(i))
+        if (worker.store.isValidPath(i)) {
+            worker.store.bumpLastUsageTime(i);
             continue;
+        }
         if (!settings.useSubstitutes)
             throw Error(
                 "dependency '%s' of '%s' does not exist, and substitution is disabled",

src/libstore/build/derivation-goal.cc

@@ -91,6 +91,7 @@ Goal::Co DerivationGoal::haveDerivation(bool storeDerivation)
 
         /* If they are all valid, then we're done. */
         if (checkResult && checkResult->second == PathStatus::Valid && buildMode == bmNormal) {
+            worker.store.bumpLastUsageTime(checkResult->first.outPath);
             co_return doneSuccess(BuildResult::Success::AlreadyValid, checkResult->first);
         }
 

src/libstore/build/derivation-trampoline-goal.cc

@@ -116,8 +116,10 @@ Goal::Co DerivationTrampolineGoal::init()
      */
     auto drv = [&] {
         for (auto * drvStore : {&worker.evalStore, &worker.store})
-            if (drvStore->isValidPath(drvPath))
+            if (drvStore->isValidPath(drvPath)) {
+                drvStore->bumpLastUsageTime(drvPath);
                 return drvStore->readDerivation(drvPath);
+            }
         assert(false);
     }();
 

src/libstore/build/entry-points.cc

@@ -92,8 +92,10 @@ BuildResult Store::buildDerivation(const StorePath & drvPath, const BasicDerivat
 void Store::ensurePath(const StorePath & path)
 {
     /* If the path is already valid, we're done. */
-    if (isValidPath(path))
+    if (isValidPath(path)) {
+        bumpLastUsageTime(path);
         return;
+    }
 
     Worker worker(*this, *this);
     GoalPtr goal = worker.makePathSubstitutionGoal(path);

src/libstore/build/substitution-goal.cc

@@ -53,6 +53,7 @@ Goal::Co PathSubstitutionGoal::init()
 
     /* If the path already exists we're done. */
     if (!repair && worker.store.isValidPath(storePath)) {
+        worker.store.bumpLastUsageTime(storePath);
         co_return doneSuccess(BuildResult::Success::AlreadyValid);
     }
 

src/libstore/derivations.cc

@@ -139,8 +139,10 @@ StorePath Store::writeDerivation(const Derivation & drv, RepairFlag repair)
 {
     auto [suffix, contents, references, path] = infoForDerivation(*this, drv);
 
-    if (isValidPath(path) && !repair)
+    if (isValidPath(path) && !repair) {
+        bumpLastUsageTime(path);
         return path;
+    }
 
     StringSource s{contents};
     auto path2 = addToStoreFromDump(

src/libstore/gc.cc

@@ -742,6 +742,12 @@ void LocalStore::collectGarbage(const GCOptions & options, GCResults & results)
             if (options.action == GCOptions::gcDeleteSpecific && !options.pathsToDelete.count(*path))
                 return;
 
+            /* If this path is too young, bail out */
+            if (options.olderThan.has_value() && options.olderThan.value() < queryPathInfo(*path)->lastUsageTime) {
+                debug("not deleting '%s' because it's too young", printStorePath(*path));
+                return markAlive();
+            }
+
             {
                 auto hashPart = path->hashPart();
                 auto shared(_shared.lock());

src/libstore/include/nix/store/gc-store.hh

@@ -55,6 +55,11 @@ struct GCOptions
      * Stop after at least `maxFreed` bytes have been freed.
      */
     uint64_t maxFreed{std::numeric_limits<uint64_t>::max()};
+
+    /**
+     * Only delete paths older than a certain point in time.
+     */
+    std::optional<time_t> olderThan;
 };
 
 struct GCResults

src/libstore/include/nix/store/local-overlay-store.hh

@@ -163,6 +163,11 @@ private:
      */
     std::optional<StorePath> queryPathFromHashPart(const std::string & hashPart) override;
 
+    /**
+     * Bump the last usage time in both the lower and upper DBs.
+     */
+    void bumpLastUsageTime(const StorePath & path) override;
+
     /**
      * First copy up any lower store realisation with the same key, so we
      * merge rather than mask it.