* Assign an integer id to every row in the ValidPaths table in order

to make the Refs table more space-efficient.  For instance, this
  reduces the size of the database on my laptop from 93 MiB to 18
  MiB.  (It was 72 MiB with the old schema on an ext3 disk with a 1
  KiB block size.)

src/libstore/local-store.cc

@@ -1230,6 +1230,8 @@ void LocalStore::upgradeStore6()
     if (sqlite3_exec(db, "begin;", 0, 0, 0) != SQLITE_OK)
         throw SQLiteError(db, "running `begin' command");
 
+    std::map<Path, sqlite3_int64> pathToId;
+    
     foreach (PathSet::iterator, i, validPaths) {
         ValidPathInfo info = queryPathInfo(*i, true);
         
@@ -1245,12 +1247,24 @@ void LocalStore::upgradeStore6()
         if (sqlite3_step(registerStmt) != SQLITE_DONE)
             throw SQLiteError(db, "registering valid path in database");
 
+        pathToId[*i] = sqlite3_last_insert_rowid(db);
+
+        std::cerr << ".";
+    }
+
+    std::cerr << "|";
+    
+    foreach (PathSet::iterator, i, validPaths) {
+        ValidPathInfo info = queryPathInfo(*i, true);
+        
         foreach (PathSet::iterator, j, info.references) {
             if (sqlite3_reset(addRefStmt) != SQLITE_OK)
                 throw SQLiteError(db, "resetting statement");
-            if (sqlite3_bind_text(addRefStmt, 1, i->c_str(), -1, SQLITE_TRANSIENT) != SQLITE_OK)
+            if (sqlite3_bind_int(addRefStmt, 1, pathToId[*i]) != SQLITE_OK)
                 throw SQLiteError(db, "binding argument 1");
-            if (sqlite3_bind_text(addRefStmt, 2, j->c_str(), -1, SQLITE_TRANSIENT) != SQLITE_OK)
+            if (pathToId.find(*j) == pathToId.end())
+                throw Error(format("path `%1%' referenced by `%2%' is invalid") % *j % *i);
+            if (sqlite3_bind_int(addRefStmt, 2, pathToId[*j]) != SQLITE_OK)
                 throw SQLiteError(db, "binding argument 2");
             if (sqlite3_step(addRefStmt) != SQLITE_DONE)
                 throw SQLiteError(db, "adding reference to database");

src/libstore/schema.sql

@@ -1,27 +1,24 @@
 pragma foreign_keys = on;
 
 create table if not exists ValidPaths (
-    path             text primary key not null,
+    id               integer primary key autoincrement not null,
+    path             text unique not null,
     hash             text not null,
     registrationTime integer not null
 );
 
 create table if not exists Refs (
-    referrer  text not null,
-    reference text not null,
+    referrer  integer not null,
+    reference integer not null,
     primary key (referrer, reference),
-    foreign key (referrer) references ValidPaths(path)
-      on delete cascade
-      deferrable initially deferred,
-    foreign key (reference) references ValidPaths(path)
-      on delete restrict
-      deferrable initially deferred
+    foreign key (referrer) references ValidPaths(id) on delete cascade,
+    foreign key (reference) references ValidPaths(id) on delete restrict
 );
 
+create index if not exists IndexReferrer on Refs(referrer);
+create index if not exists IndexReference on Refs(reference);
+
 create table if not exists FailedDerivations (
     path text primary key not null,
     time integer not null
 );
-
-create index IndexReferrer on Refs(referrer);
-create index IndexReference on Refs(reference);