* Revert r19650 (implement gc-keep-outputs by looking for derivations

with the same name as the output) and instead use the
  DerivationOutputs table in the database, which is the correct way to
  to do things.

src/libstore/gc.cc

@@ -416,12 +416,7 @@ struct LocalStore::GCState
     PathSet busy;
     bool gcKeepOutputs;
     bool gcKeepDerivations;
-
-    bool drvsIndexed;
-    typedef std::multimap<string, Path> DrvsByName;
-    DrvsByName drvsByName; // derivation paths hashed by name attribute
-
-    GCState(GCResults & results_) : results(results_), drvsIndexed(false)
+    GCState(GCResults & results_) : results(results_)
     {
     }
 };
@@ -441,42 +436,6 @@ bool LocalStore::isActiveTempFile(const GCState & state,
         && state.tempRoots.find(string(path, 0, path.size() - suffix.size())) != state.tempRoots.end();
 }
 
-
-/* Return all the derivations in the Nix store that have `path' as an
-   output.  This function assumes that derivations have the same name
-   as their outputs. */
-PathSet LocalStore::findDerivers(GCState & state, const Path & path)
-{
-    PathSet derivers;
-
-    Path deriver = queryDeriver(path);
-    if (deriver != "") derivers.insert(deriver);
-
-    if (!state.drvsIndexed) {
-        Paths entries = readDirectory(nixStore);
-        foreach (Paths::iterator, i, entries)
-            if (isDerivation(*i))
-                state.drvsByName.insert(std::pair<string, Path>(
-                        getNameOfStorePath(*i), nixStore + "/" + *i));
-        state.drvsIndexed = true;
-    }
-    
-    string name = getNameOfStorePath(path);
-
-    // Urgh, I should have used Haskell...
-    std::pair<GCState::DrvsByName::iterator, GCState::DrvsByName::iterator> range =
-        state.drvsByName.equal_range(name);
-
-    for (GCState::DrvsByName::iterator i = range.first; i != range.second; ++i)
-        if (isValidPath(i->second)) {
-            Derivation drv = derivationFromPath(i->second);
-            foreach (DerivationOutputs::iterator, j, drv.outputs)
-                if (j->second.path == path) derivers.insert(i->second);
-        }
-
-    return derivers;
-}
-
     
 bool LocalStore::tryToDelete(GCState & state, const Path & path)
 {
@@ -522,18 +481,9 @@ bool LocalStore::tryToDelete(GCState & state, const Path & path)
         if (!pathExists(path)) return true;
 
         /* If gc-keep-outputs is set, then don't delete this path if
-           its deriver is not garbage.  !!! Nix does not reliably
-           store derivers, so we have to look at all derivations to
-           determine which of them derive `path'.  Since this makes
-           the garbage collector very slow to start on large Nix
-           stores, here we just look for all derivations that have the
-           same name as `path' (where the name is the part of the
-           filename after the hash, i.e. the `name' attribute of the
-           derivation).  This is somewhat hacky: currently, the
-           deriver of a path always has the same name as the output,
-           but this might change in the future. */
+           there are derivers of this path that are not garbage. */
         if (state.gcKeepOutputs) {
-            PathSet derivers = findDerivers(state, path);
+            PathSet derivers = queryValidDerivers(path);
             foreach (PathSet::iterator, deriver, derivers) {
                 /* Break an infinite recursion if gc-keep-derivations
                    and gc-keep-outputs are both set by tentatively

src/libstore/local-store.cc

@@ -297,6 +297,8 @@ void LocalStore::prepareStatements()
         "select time from FailedPaths where path = ?;");
     stmtAddDerivationOutput.create(db,
         "insert or replace into DerivationOutputs (drv, id, path) values (?, ?, ?);");
+    stmtQueryValidDerivers.create(db,
+        "select v.id, v.path from DerivationOutputs d join ValidPaths v on d.drv = v.id where d.path = ?;");
 }
 
 
@@ -599,6 +601,28 @@ Path LocalStore::queryDeriver(const Path & path)
 }
 
 
+PathSet LocalStore::queryValidDerivers(const Path & path)
+{
+    assertStorePath(path);
+
+    SQLiteStmtUse use(stmtQueryValidDerivers);
+    stmtQueryValidDerivers.bind(path);
+
+    PathSet derivers;
+    int r;
+    while ((r = sqlite3_step(stmtQueryValidDerivers)) == SQLITE_ROW) {
+        const char * s = (const char *) sqlite3_column_text(stmtQueryValidDerivers, 1);
+        assert(s);
+        derivers.insert(s);
+    }
+    
+    if (r != SQLITE_DONE)
+        throw SQLiteError(db, format("error getting valid derivers of `%1%'") % path);
+    
+    return derivers;
+}
+
+
 void LocalStore::startSubstituter(const Path & substituter, RunningSubstituter & run)
 {
     if (run.pid != -1) return;

src/libstore/local-store.hh

@@ -103,6 +103,12 @@ public:
     void queryReferrers(const Path & path, PathSet & referrers);
 
     Path queryDeriver(const Path & path);
+
+    /* Return all currently valid derivations that have `path' as an
+       output.  (Note that the result of `queryDeriver()' is the
+       derivation that was actually used to produce `path', which may
+       not exist anymore.) */
+    PathSet queryValidDerivers(const Path & path);
     
     PathSet querySubstitutablePaths();
     
@@ -199,6 +205,7 @@ private:
     SQLiteStmt stmtRegisterFailedPath;
     SQLiteStmt stmtHasPathFailed;
     SQLiteStmt stmtAddDerivationOutput;
+    SQLiteStmt stmtQueryValidDerivers;
 
     int getSchema();
 
@@ -228,8 +235,6 @@ private:
 
     bool tryToDelete(GCState & state, const Path & path);
     
-    PathSet findDerivers(GCState & state, const Path & path);
-    
     bool isActiveTempFile(const GCState & state,
         const Path & path, const string & suffix);
         

src/libstore/store-api.cc

@@ -1,7 +1,6 @@
 #include "store-api.hh"
 #include "globals.hh"
 #include "util.hh"
-#include "derivations.hh"
 
 #include <limits.h>
 
@@ -53,18 +52,6 @@ Path toStorePath(const Path & path)
 }
 
 
-string getNameOfStorePath(const Path & path)
-{
-    Path::size_type slash = path.rfind('/');
-    string p = slash == Path::npos ? path : string(path, slash + 1);
-    Path::size_type dash = p.find('-');
-    assert(dash != Path::npos);
-    string p2 = string(p, dash + 1);
-    if (isDerivation(p2)) p2 = string(p2, 0, p2.size() - 4);
-    return p2;
-}
-
-
 Path followLinksToStore(const Path & _path)
 {
     Path path = absPath(_path);

src/libstore/store-api.hh

@@ -243,12 +243,6 @@ void checkStoreName(const string & name);
 Path toStorePath(const Path & path);
 
 
-/* Get the "name" part of a store path, that is, the part after the
-   hash and the dash, and with any ".drv" suffix removed
-   (e.g. /nix/store/<hash>-foo-1.2.3.drv => foo-1.2.3). */
-string getNameOfStorePath(const Path & path);
-
-
 /* Follow symlinks until we end up with a path in the Nix store. */
 Path followLinksToStore(const Path & path);