diff --git a/base/clock.rs b/base/clock.rs
index 73a5f89..8c63edf 100644
--- a/base/clock.rs
+++ b/base/clock.rs
@@ -62,7 +62,7 @@ pub fn retry_forever<T, E: Into<Error>>(clocks: &Clocks, f: &mut FnMut() -> Resu
     }
 }
 
-#[derive(Clone)]
+#[derive(Copy, Clone)]
 pub struct RealClocks {}
 
 impl RealClocks {
diff --git a/db/db.rs b/db/db.rs
index 3ae1663..093138c 100644
--- a/db/db.rs
+++ b/db/db.rs
@@ -52,7 +52,7 @@
 //!     A list of mutations is built up in-memory and occasionally flushed to reduce SSD write
 //!     cycles.
 
-use base::clock::Clocks;
+use base::clock::{self, Clocks};
 use dir;
 use failure::Error;
 use fnv::{self, FnvHashMap, FnvHashSet};
@@ -565,7 +565,6 @@ fn init_recordings(conn: &mut rusqlite::Connection, stream_id: i32, camera: &Cam
 }
 
 pub struct LockedDatabase {
-    clocks: Arc<Clocks>,
     conn: rusqlite::Connection,
     uuid: Uuid,
 
@@ -812,16 +811,10 @@ impl LockedDatabase {
         Ok(())
     }
 
-    /// Tries to flush unwritten changes from the stream directories.
+    /// Helper for `DatabaseGuard::flush()` and `Database::drop()`.
     ///
-    ///    * commits any recordings added with `add_recording` that have since been marked as
-    ///      synced.
-    ///    * moves old recordings to the garbage table as requested by `delete_oldest_recordings`.
-    ///    * removes entries from the garbage table as requested by `mark_sample_files_deleted`.
-    ///
-    /// On success, for each affected sample file directory with a flush watcher set, sends a
-    /// `Flush` event.
-    pub(crate) fn flush(&mut self, reason: &str) -> Result<(), Error> {
+    /// The public API is in `DatabaseGuard::flush()`; it supplies the `Clocks` to this function.
+    fn flush<C: Clocks>(&mut self, clocks: &C, reason: &str) -> Result<(), Error> {
         let o = match self.open.as_ref() {
             None => bail!("database is read-only"),
             Some(o) => o,
@@ -873,8 +866,8 @@ impl LockedDatabase {
             let mut stmt = tx.prepare_cached(
                 r"update open set duration_90k = ?, end_time_90k = ? where id = ?")?;
             let rows = stmt.execute(&[
-                &(recording::Time::new(self.clocks.monotonic()) - self.open_monotonic).0,
-                &recording::Time::new(self.clocks.realtime()).0,
+                &(recording::Time::new(clocks.monotonic()) - self.open_monotonic).0,
+                &recording::Time::new(clocks.realtime()).0,
                 &o.id,
             ])?;
             if rows != 1 {
@@ -1692,6 +1685,21 @@ impl LockedDatabase {
     }
 }
 
+/// Initializes a database.
+/// Note this doesn't set journal options, so that it can be used on in-memory databases for
+/// test code.
+pub fn init(conn: &mut rusqlite::Connection) -> Result<(), Error> {
+    let tx = conn.transaction()?;
+    tx.execute_batch(include_str!("schema.sql"))?;
+    {
+        let uuid = ::uuid::Uuid::new_v4();
+        let uuid_bytes = &uuid.as_bytes()[..];
+        tx.execute("insert into meta (uuid) values (?)", &[&uuid_bytes])?;
+    }
+    tx.commit()?;
+    Ok(())
+}
+
 /// Gets the schema version from the given database connection.
 /// A fully initialized database will return `Ok(Some(version))` where `version` is an integer that
 /// can be compared to `EXPECTED_VERSION`. An empty database will return `Ok(None)`. A partially
@@ -1709,28 +1717,37 @@ pub fn get_schema_version(conn: &rusqlite::Connection) -> Result<Option<i32>, Er
 /// The recording database. Abstracts away SQLite queries. Also maintains in-memory state
 /// (loaded on startup, and updated on successful commit) to avoid expensive scans over the
 /// recording table on common queries.
-pub struct Database(
+pub struct Database<C: Clocks + Clone = clock::RealClocks> {
     /// This is wrapped in an `Option` to allow the `Drop` implementation and `close` to coexist.
-    Option<Mutex<LockedDatabase>>
-);
+    db: Option<Mutex<LockedDatabase>>,
 
-impl Drop for Database {
+    /// This is kept separately from the `LockedDatabase` to allow the `lock()` operation itself to
+    /// access it. It doesn't need a `Mutex` anyway; it's `Sync`, and all operations work on
+    /// `&self`.
+    clocks: C,
+}
+
+impl<C: Clocks + Clone> Drop for Database<C> {
     fn drop(&mut self) {
         if ::std::thread::panicking() {
             return;  // don't flush while panicking.
         }
-        if let Some(m) = self.0.take() {
-            if let Err(e) = m.into_inner().flush("drop") {
+        if let Some(m) = self.db.take() {
+            if let Err(e) = m.into_inner().flush(&self.clocks, "drop") {
                 error!("Final database flush failed: {}", e);
             }
         }
     }
 }
 
-impl Database {
+// Helpers for Database::lock(). Closures don't implement Fn.
+fn acquisition() -> &'static str { "database lock acquisition" }
+fn operation() -> &'static str { "database operation" }
+
+impl<C: Clocks + Clone> Database<C> {
     /// Creates the database from a caller-supplied SQLite connection.
-    pub fn new(clocks: Arc<Clocks>, conn: rusqlite::Connection,
-               read_write: bool) -> Result<Database, Error> {
+    pub fn new(clocks: C, conn: rusqlite::Connection,
+               read_write: bool) -> Result<Database<C>, Error> {
         conn.execute("pragma foreign_keys = on", &[])?;
         {
             let ver = get_schema_version(&conn)?.ok_or_else(|| format_err!(
@@ -1767,20 +1784,22 @@ impl Database {
                 uuid,
             })
         } else { None };
-        let db = Database(Some(Mutex::new(LockedDatabase {
+        let db = Database {
+            db: Some(Mutex::new(LockedDatabase {
+                conn,
+                uuid,
+                open,
+                open_monotonic,
+                sample_file_dirs_by_id: BTreeMap::new(),
+                cameras_by_id: BTreeMap::new(),
+                cameras_by_uuid: BTreeMap::new(),
+                streams_by_id: BTreeMap::new(),
+                video_sample_entries_by_id: BTreeMap::new(),
+                video_index_cache: RefCell::new(LruCache::with_hasher(1024, Default::default())),
+                on_flush: Vec::new(),
+            })),
             clocks,
-            conn,
-            uuid,
-            open,
-            open_monotonic,
-            sample_file_dirs_by_id: BTreeMap::new(),
-            cameras_by_id: BTreeMap::new(),
-            cameras_by_uuid: BTreeMap::new(),
-            streams_by_id: BTreeMap::new(),
-            video_sample_entries_by_id: BTreeMap::new(),
-            video_index_cache: RefCell::new(LruCache::with_hasher(1024, Default::default())),
-            on_flush: Vec::new(),
-        })));
+        };
         {
             let l = &mut *db.lock();
             l.init_video_sample_entries()?;
@@ -1796,35 +1815,62 @@ impl Database {
         Ok(db)
     }
 
-    /// Initializes a database.
-    /// Note this doesn't set journal options, so that it can be used on in-memory databases for
-    /// test code.
-    pub fn init(conn: &mut rusqlite::Connection) -> Result<(), Error> {
-        let tx = conn.transaction()?;
-        tx.execute_batch(include_str!("schema.sql"))?;
-        {
-            let uuid = ::uuid::Uuid::new_v4();
-            let uuid_bytes = &uuid.as_bytes()[..];
-            tx.execute("insert into meta (uuid) values (?)", &[&uuid_bytes])?;
-        }
-        tx.commit()?;
-        Ok(())
-    }
+    #[inline(always)]
+    pub fn clocks(&self) -> C { self.clocks.clone() }
 
     /// Locks the database; the returned reference is the only way to perform (read or write)
     /// operations.
-    pub fn lock(&self) -> MutexGuard<LockedDatabase> {
-        self.0.as_ref().unwrap().lock()
+    pub fn lock(&self) -> DatabaseGuard<C> {
+        let timer = clock::TimerGuard::new(&self.clocks, acquisition);
+        let db = self.db.as_ref().unwrap().lock();
+        drop(timer);
+        let _timer = clock::TimerGuard::<C, &'static str, fn() -> &'static str>::new(
+            &self.clocks, operation);
+        DatabaseGuard {
+            clocks: &self.clocks,
+            db,
+            _timer,
+        }
     }
 
     /// For testing: closes the database (without flushing) and returns the connection.
     /// This allows verification that a newly opened database is in an acceptable state.
     #[cfg(test)]
     fn close(mut self) -> rusqlite::Connection {
-        self.0.take().unwrap().into_inner().conn
+        self.db.take().unwrap().into_inner().conn
     }
 }
 
+pub struct DatabaseGuard<'db, C: Clocks> {
+    clocks: &'db C,
+    db: MutexGuard<'db, LockedDatabase>,
+    _timer: clock::TimerGuard<'db, C, &'static str, fn() -> &'static str>,
+}
+
+impl<'db, C: Clocks + Clone> DatabaseGuard<'db, C> {
+    /// Tries to flush unwritten changes from the stream directories.
+    ///
+    ///    * commits any recordings added with `add_recording` that have since been marked as
+    ///      synced.
+    ///    * moves old recordings to the garbage table as requested by `delete_oldest_recordings`.
+    ///    * removes entries from the garbage table as requested by `mark_sample_files_deleted`.
+    ///
+    /// On success, for each affected sample file directory with a flush watcher set, sends a
+    /// `Flush` event.
+    pub(crate) fn flush(&mut self, reason: &str) -> Result<(), Error> {
+        self.db.flush(self.clocks, reason)
+    }
+}
+
+impl<'db, C: Clocks + Clone> ::std::ops::Deref for DatabaseGuard<'db, C> {
+    type Target = LockedDatabase;
+    fn deref(&self) -> &LockedDatabase { &*self.db }
+}
+
+impl<'db, C: Clocks + Clone> ::std::ops::DerefMut for DatabaseGuard<'db, C> {
+    fn deref_mut(&mut self) -> &mut LockedDatabase { &mut *self.db }
+}
+
 #[cfg(test)]
 mod tests {
     extern crate tempdir;
@@ -1840,7 +1886,7 @@ mod tests {
 
     fn setup_conn() -> Connection {
         let mut conn = Connection::open_in_memory().unwrap();
-        Database::init(&mut conn).unwrap();
+        super::init(&mut conn).unwrap();
         conn
     }
 
@@ -1995,7 +2041,7 @@ mod tests {
     #[test]
     fn test_no_meta_or_version() {
         testutil::init();
-        let e = Database::new(Arc::new(clock::RealClocks{}), Connection::open_in_memory().unwrap(),
+        let e = Database::new(clock::RealClocks {}, Connection::open_in_memory().unwrap(),
                               false).err().unwrap();
         assert!(e.to_string().starts_with("no such table"), "{}", e);
     }
@@ -2005,7 +2051,7 @@ mod tests {
         testutil::init();
         let c = setup_conn();
         c.execute_batch("delete from version; insert into version values (2, 0, '');").unwrap();
-        let e = Database::new(Arc::new(clock::RealClocks{}), c, false).err().unwrap();
+        let e = Database::new(clock::RealClocks {}, c, false).err().unwrap();
         assert!(e.to_string().starts_with(
                 "Database schema version 2 is too old (expected 3)"), "got: {:?}", e);
     }
@@ -2015,7 +2061,7 @@ mod tests {
         testutil::init();
         let c = setup_conn();
         c.execute_batch("delete from version; insert into version values (4, 0, '');").unwrap();
-        let e = Database::new(Arc::new(clock::RealClocks{}), c, false).err().unwrap();
+        let e = Database::new(clock::RealClocks {}, c, false).err().unwrap();
         assert!(e.to_string().starts_with(
                 "Database schema version 4 is too new (expected 3)"), "got: {:?}", e);
     }
@@ -2025,7 +2071,7 @@ mod tests {
     fn test_fresh_db() {
         testutil::init();
         let conn = setup_conn();
-        let db = Database::new(Arc::new(clock::RealClocks{}), conn, true).unwrap();
+        let db = Database::new(clock::RealClocks {}, conn, true).unwrap();
         let db = db.lock();
         assert_eq!(0, db.cameras_by_id().values().count());
     }
@@ -2035,7 +2081,7 @@ mod tests {
     fn test_full_lifecycle() {
         testutil::init();
         let conn = setup_conn();
-        let db = Database::new(Arc::new(clock::RealClocks{}), conn, true).unwrap();
+        let db = Database::new(clock::RealClocks {}, conn, true).unwrap();
         let tmpdir = tempdir::TempDir::new("moonfire-nvr-test").unwrap();
         let path = tmpdir.path().to_str().unwrap().to_owned();
         let sample_file_dir_id = { db.lock() }.add_sample_file_dir(path).unwrap();
@@ -2091,7 +2137,7 @@ mod tests {
 
         // Closing and reopening the database should present the same contents.
         let conn = db.close();
-        let db = Database::new(Arc::new(clock::RealClocks{}), conn, true).unwrap();
+        let db = Database::new(clock::RealClocks {}, conn, true).unwrap();
         assert_eq!(db.lock().streams_by_id().get(&sub_stream_id).unwrap().flush_if_sec, 2);
         assert_no_recordings(&db, camera_uuid);
 
@@ -2132,7 +2178,7 @@ mod tests {
         // Queries on a fresh database should return the correct result (with caches populated from
         // existing database contents rather than built on insert).
         let conn = db.close();
-        let db = Database::new(Arc::new(clock::RealClocks{}), conn, true).unwrap();
+        let db = Database::new(clock::RealClocks {}, conn, true).unwrap();
         assert_single_recording(&db, main_stream_id, &recording);
 
         // Deleting a recording should succeed, update the min/max times, and mark it as garbage.
diff --git a/db/recording.rs b/db/recording.rs
index f11f1ec..ed16272 100644
--- a/db/recording.rs
+++ b/db/recording.rs
@@ -498,6 +498,7 @@ impl Segment {
 
 #[cfg(test)]
 mod tests {
+    use base::clock::RealClocks;
     use super::*;
     use testutil::{self, TestDb};
 
@@ -643,7 +644,7 @@ mod tests {
             let bytes = 3 * i;
             encoder.add_sample(duration_90k, bytes, true, &mut r);
         }
-        let db = TestDb::new();
+        let db = TestDb::new(RealClocks {});
         let row = db.insert_recording_from_encoder(r);
         // Time range [2, 2 + 4 + 6 + 8) means the 2nd, 3rd, 4th samples should be
         // included.
@@ -662,7 +663,7 @@ mod tests {
             let bytes = 3 * i;
             encoder.add_sample(duration_90k, bytes, (i % 2) == 1, &mut r);
         }
-        let db = TestDb::new();
+        let db = TestDb::new(RealClocks {});
         let row = db.insert_recording_from_encoder(r);
         // Time range [2 + 4 + 6, 2 + 4 + 6 + 8) means the 4th sample should be included.
         // The 3rd also gets pulled in because it is a sync frame and the 4th is not.
@@ -678,7 +679,7 @@ mod tests {
         encoder.add_sample(1, 1, true, &mut r);
         encoder.add_sample(1, 2, true, &mut r);
         encoder.add_sample(0, 3, true, &mut r);
-        let db = TestDb::new();
+        let db = TestDb::new(RealClocks {});
         let row = db.insert_recording_from_encoder(r);
         let segment = Segment::new(&db.db.lock(), &row, 1 .. 2).unwrap();
         assert_eq!(&get_frames(&db.db, &segment, |it| it.bytes), &[2, 3]);
@@ -691,7 +692,7 @@ mod tests {
         let mut r = db::RecordingToInsert::default();
         let mut encoder = SampleIndexEncoder::new();
         encoder.add_sample(1, 1, true, &mut r);
-        let db = TestDb::new();
+        let db = TestDb::new(RealClocks {});
         let row = db.insert_recording_from_encoder(r);
         let segment = Segment::new(&db.db.lock(), &row, 0 .. 0).unwrap();
         assert_eq!(&get_frames(&db.db, &segment, |it| it.bytes), &[1]);
@@ -709,7 +710,7 @@ mod tests {
             let bytes = 3 * i;
             encoder.add_sample(duration_90k, bytes, (i % 2) == 1, &mut r);
         }
-        let db = TestDb::new();
+        let db = TestDb::new(RealClocks {});
         let row = db.insert_recording_from_encoder(r);
         let segment = Segment::new(&db.db.lock(), &row, 0 .. 2+4+6+8+10).unwrap();
         assert_eq!(&get_frames(&db.db, &segment, |it| it.duration_90k), &[2, 4, 6, 8, 10]);
@@ -723,7 +724,7 @@ mod tests {
         encoder.add_sample(1, 1, true, &mut r);
         encoder.add_sample(1, 2, true, &mut r);
         encoder.add_sample(0, 3, true, &mut r);
-        let db = TestDb::new();
+        let db = TestDb::new(RealClocks {});
         let row = db.insert_recording_from_encoder(r);
         let segment = Segment::new(&db.db.lock(), &row, 0 .. 2).unwrap();
         assert_eq!(&get_frames(&db.db, &segment, |it| it.bytes), &[1, 2, 3]);
diff --git a/db/testutil.rs b/db/testutil.rs
index 3ce83e6..d7cfa99 100644
--- a/db/testutil.rs
+++ b/db/testutil.rs
@@ -28,7 +28,7 @@
 // You should have received a copy of the GNU General Public License
 // along with this program.  If not, see <http://www.gnu.org/licenses/>.
 
-use base::clock;
+use base::clock::Clocks;
 use db;
 use dir;
 use fnv::FnvHashMap;
@@ -64,8 +64,8 @@ pub fn init() {
     });
 }
 
-pub struct TestDb {
-    pub db: Arc<db::Database>,
+pub struct TestDb<C: Clocks + Clone> {
+    pub db: Arc<db::Database<C>>,
     pub dirs_by_stream_id: Arc<FnvHashMap<i32, Arc<dir::SampleFileDir>>>,
     pub syncer_channel: writer::SyncerChannel<::std::fs::File>,
     pub syncer_join: thread::JoinHandle<()>,
@@ -73,14 +73,13 @@ pub struct TestDb {
     pub test_camera_uuid: Uuid,
 }
 
-impl TestDb {
+impl<C: Clocks + Clone> TestDb<C> {
     /// Creates a test database with one camera.
-    pub fn new() -> TestDb {
+    pub fn new(clocks: C) -> Self {
         let tmpdir = TempDir::new("moonfire-nvr-test").unwrap();
 
-        let clocks = Arc::new(clock::RealClocks{});
         let mut conn = rusqlite::Connection::open_in_memory().unwrap();
-        db::Database::init(&mut conn).unwrap();
+        db::init(&mut conn).unwrap();
         let db = Arc::new(db::Database::new(clocks, conn, true).unwrap());
         let (test_camera_uuid, sample_file_dir_id);
         let path = tmpdir.path().to_str().unwrap().to_owned();
diff --git a/db/writer.rs b/db/writer.rs
index 921ce81..55c7488 100644
--- a/db/writer.rs
+++ b/db/writer.rs
@@ -97,11 +97,10 @@ impl<F> ::std::clone::Clone for SyncerChannel<F> {
 }
 
 /// State of the worker thread.
-struct Syncer<C: Clocks, D: DirWriter> {
-    clocks: C,
+struct Syncer<C: Clocks + Clone, D: DirWriter> {
     dir_id: i32,
     dir: D,
-    db: Arc<db::Database>,
+    db: Arc<db::Database<C>>,
 }
 
 /// Starts a syncer for the given sample file directory.
@@ -121,8 +120,9 @@ struct Syncer<C: Clocks, D: DirWriter> {
 /// Note that dropping all `SyncerChannel` clones currently includes calling
 /// `LockedDatabase::clear_on_flush`, as this function installs a hook to watch database flushes.
 /// TODO: add a join wrapper which arranges for the on flush hook to be removed automatically.
-pub fn start_syncer(db: Arc<db::Database>, dir_id: i32)
-                    -> Result<(SyncerChannel<::std::fs::File>, thread::JoinHandle<()>), Error> {
+pub fn start_syncer<C>(db: Arc<db::Database<C>>, dir_id: i32)
+                       -> Result<(SyncerChannel<::std::fs::File>, thread::JoinHandle<()>), Error>
+where C: Clocks + Clone {
     let db2 = db.clone();
     let (mut syncer, path) = Syncer::new(&db.lock(), db2, dir_id)?;
     syncer.initial_rotation()?;
@@ -216,8 +216,30 @@ impl<F: FileWriter> SyncerChannel<F> {
     }
 }
 
-impl Syncer<clock::RealClocks, Arc<dir::SampleFileDir>> {
-    fn new(l: &db::LockedDatabase, db: Arc<db::Database>, dir_id: i32)
+/// Lists files which should be "abandoned" (deleted without ever recording in the database)
+/// on opening.
+fn list_files_to_abandon(path: &str, streams_to_next: FnvHashMap<i32, i32>)
+                         -> Result<Vec<CompositeId>, Error> {
+    let mut v = Vec::new();
+    for e in ::std::fs::read_dir(path)? {
+        let e = e?;
+        let id = match dir::parse_id(e.file_name().as_bytes()) {
+            Ok(i) => i,
+            Err(_) => continue,
+        };
+        let next = match streams_to_next.get(&id.stream()) {
+            Some(n) => *n,
+            None => continue,  // unknown stream.
+        };
+        if id.recording() >= next {
+            v.push(id);
+        }
+    }
+    Ok(v)
+}
+
+impl<C: Clocks + Clone> Syncer<C, Arc<dir::SampleFileDir>> {
+    fn new(l: &db::LockedDatabase, db: Arc<db::Database<C>>, dir_id: i32)
            -> Result<(Self, String), Error> {
         let d = l.sample_file_dirs_by_id()
                  .get(&dir_id)
@@ -237,7 +259,7 @@ impl Syncer<clock::RealClocks, Arc<dir::SampleFileDir>> {
                  }
              })
              .collect();
-        let to_abandon = Syncer::list_files_to_abandon(&d.path, streams_to_next)?;
+        let to_abandon = list_files_to_abandon(&d.path, streams_to_next)?;
         let mut undeletable = 0;
         for &id in &to_abandon {
             if let Err(e) = dir.unlink_file(id) {
@@ -254,35 +276,12 @@ impl Syncer<clock::RealClocks, Arc<dir::SampleFileDir>> {
         }
 
         Ok((Syncer {
-            clocks: clock::RealClocks{},
             dir_id,
             dir,
             db,
         }, d.path.clone()))
     }
 
-    /// Lists files which should be "abandoned" (deleted without ever recording in the database)
-    /// on opening.
-    fn list_files_to_abandon(path: &str, streams_to_next: FnvHashMap<i32, i32>)
-                             -> Result<Vec<CompositeId>, Error> {
-        let mut v = Vec::new();
-        for e in ::std::fs::read_dir(path)? {
-            let e = e?;
-            let id = match dir::parse_id(e.file_name().as_bytes()) {
-                Ok(i) => i,
-                Err(_) => continue,
-            };
-            let next = match streams_to_next.get(&id.stream()) {
-                Some(n) => *n,
-                None => continue,  // unknown stream.
-            };
-            if id.recording() >= next {
-                v.push(id);
-            }
-        }
-        Ok(v)
-    }
-
     /// Rotates files for all streams and deletes stale files from previous runs.
     /// Called from main thread.
     fn initial_rotation(&mut self) -> Result<(), Error> {
@@ -331,7 +330,7 @@ impl Syncer<clock::RealClocks, Arc<dir::SampleFileDir>> {
     }
 }
 
-impl<C: Clocks, D: DirWriter> Syncer<C, D> {
+impl<C: Clocks + Clone, D: DirWriter> Syncer<C, D> {
     fn run(&mut self, cmds: mpsc::Receiver<SyncerCommand<D::File>>) {
         loop {
             match cmds.recv() {
@@ -353,7 +352,7 @@ impl<C: Clocks, D: DirWriter> Syncer<C, D> {
         if garbage.is_empty() {
             return;
         }
-        let c = &self.clocks;
+        let c = &self.db.clocks();
         for &id in &garbage {
             clock::retry_forever(c, &mut || {
                 if let Err(e) = self.dir.unlink_file(id) {
@@ -380,8 +379,8 @@ impl<C: Clocks, D: DirWriter> Syncer<C, D> {
         let stream_id = id.stream();
 
         // Free up a like number of bytes.
-        clock::retry_forever(&self.clocks, &mut || f.sync_all());
-        clock::retry_forever(&self.clocks, &mut || self.dir.sync());
+        clock::retry_forever(&self.db.clocks(), &mut || f.sync_all());
+        clock::retry_forever(&self.db.clocks(), &mut || self.dir.sync());
         let mut db = self.db.lock();
         db.mark_synced(id).unwrap();
         delete_recordings(&mut db, stream_id, 0).unwrap();
@@ -412,10 +411,9 @@ impl<C: Clocks, D: DirWriter> Syncer<C, D> {
 /// metadata to the database. `Writer` hands off each recording's state to the syncer when done. It
 /// saves the recording to the database (if I/O errors do not prevent this), retries forever,
 /// or panics (if further writing on this stream is impossible).
-pub struct Writer<'a, C: Clocks, D: DirWriter> {
-    clocks: &'a C,
+pub struct Writer<'a, C: Clocks + Clone, D: DirWriter> {
     dir: &'a D,
-    db: &'a db::Database,
+    db: &'a db::Database<C>,
     channel: &'a SyncerChannel<D::File>,
     stream_id: i32,
     video_sample_entry_id: i32,
@@ -523,11 +521,10 @@ struct PreviousWriter {
     run_offset: i32,
 }
 
-impl<'a, C: Clocks, D: DirWriter> Writer<'a, C, D> {
-    pub fn new(clocks: &'a C, dir: &'a D, db: &'a db::Database, channel: &'a SyncerChannel<D::File>,
+impl<'a, C: Clocks + Clone, D: DirWriter> Writer<'a, C, D> {
+    pub fn new(dir: &'a D, db: &'a db::Database<C>, channel: &'a SyncerChannel<D::File>,
                stream_id: i32, video_sample_entry_id: i32) -> Self {
         Writer {
-            clocks,
             dir,
             db,
             channel,
@@ -553,7 +550,7 @@ impl<'a, C: Clocks, D: DirWriter> Writer<'a, C, D> {
             flags: db::RecordingFlags::Growing as i32,
             ..Default::default()
         })?;
-        let f = clock::retry_forever(self.clocks, &mut || self.dir.create_file(id));
+        let f = clock::retry_forever(&self.db.clocks(), &mut || self.dir.create_file(id));
 
         self.state = WriterState::Open(InnerWriter {
             f,
@@ -601,7 +598,7 @@ impl<'a, C: Clocks, D: DirWriter> Writer<'a, C, D> {
         }
         let mut remaining = pkt;
         while !remaining.is_empty() {
-            let written = clock::retry_forever(self.clocks, &mut || w.f.write(remaining));
+            let written = clock::retry_forever(&self.db.clocks(), &mut || w.f.write(remaining));
             remaining = &remaining[written..];
         }
         w.unflushed_sample = Some(UnflushedSample {
@@ -669,7 +666,7 @@ impl<F: FileWriter> InnerWriter<F> {
     }
 }
 
-impl<'a, C: Clocks, D: DirWriter> Drop for Writer<'a, C, D> {
+impl<'a, C: Clocks + Clone, D: DirWriter> Drop for Writer<'a, C, D> {
     fn drop(&mut self) {
         if ::std::thread::panicking() {
             // This will probably panic again. Don't do it.
@@ -779,8 +776,8 @@ mod tests {
     }
 
     struct Harness {
-        clocks: SimulatedClocks,
-        db: Arc<db::Database>,
+        //clocks: SimulatedClocks,
+        db: Arc<db::Database<SimulatedClocks>>,
         dir_id: i32,
         _tmpdir: ::tempdir::TempDir,
         dir: MockDir,
@@ -789,7 +786,8 @@ mod tests {
     }
 
     fn new_harness() -> Harness {
-        let tdb = testutil::TestDb::new();
+        let clocks = SimulatedClocks::new(::time::Timespec::new(0, 0));
+        let tdb = testutil::TestDb::new(clocks);
         let dir_id = *tdb.db.lock().sample_file_dirs_by_id().keys().next().unwrap();
 
         // This starts a real fs-backed syncer. Get rid of it.
@@ -798,10 +796,8 @@ mod tests {
         tdb.syncer_join.join().unwrap();
 
         // Start a mocker syncer.
-        let clocks = SimulatedClocks::new(::time::Timespec::new(0, 0));
         let dir = MockDir::new();
         let mut syncer = super::Syncer {
-            clocks: clocks.clone(),
             dir_id: *tdb.db.lock().sample_file_dirs_by_id().keys().next().unwrap(),
             dir: dir.clone(),
             db: tdb.db.clone(),
@@ -818,7 +814,7 @@ mod tests {
             .spawn(move || syncer.run(rcv)).unwrap();
 
         Harness {
-            clocks,
+            //clocks,
             dir_id,
             dir,
             db: tdb.db,
@@ -837,7 +833,7 @@ mod tests {
         let video_sample_entry_id = h.db.lock().insert_video_sample_entry(
             1920, 1080, [0u8; 100].to_vec(), "avc1.000000".to_owned()).unwrap();
         {
-            let mut w = Writer::new(&h.clocks, &h.dir, &h.db, &h.channel, testutil::TEST_STREAM_ID,
+            let mut w = Writer::new(&h.dir, &h.db, &h.channel, testutil::TEST_STREAM_ID,
                                     video_sample_entry_id);
             h.dir.expect(MockDirAction::Create(CompositeId::new(1, 1), Box::new(|_id| Err(eio()))));
             let f = MockFile::new();
@@ -895,7 +891,7 @@ mod tests {
         let video_sample_entry_id = h.db.lock().insert_video_sample_entry(
             1920, 1080, [0u8; 100].to_vec(), "avc1.000000".to_owned()).unwrap();
         {
-            let mut w = Writer::new(&h.clocks, &h.dir, &h.db, &h.channel, testutil::TEST_STREAM_ID,
+            let mut w = Writer::new(&h.dir, &h.db, &h.channel, testutil::TEST_STREAM_ID,
                                     video_sample_entry_id);
             let f = MockFile::new();
             h.dir.expect(MockDirAction::Create(CompositeId::new(1, 1),
diff --git a/src/cmds/config/mod.rs b/src/cmds/config/mod.rs
index bdae46f..90169ac 100644
--- a/src/cmds/config/mod.rs
+++ b/src/cmds/config/mod.rs
@@ -125,7 +125,7 @@ struct Args {
 pub fn run() -> Result<(), Error> {
     let args: Args = super::parse_args(USAGE)?;
     let (_db_dir, conn) = super::open_conn(&args.flag_db_dir, super::OpenMode::ReadWrite)?;
-    let clocks = Arc::new(clock::RealClocks{});
+    let clocks = clock::RealClocks {};
     let db = Arc::new(db::Database::new(clocks, conn, true)?);
 
     let mut siv = Cursive::new();
diff --git a/src/cmds/init.rs b/src/cmds/init.rs
index f2b8a58..b0f91f1 100644
--- a/src/cmds/init.rs
+++ b/src/cmds/init.rs
@@ -66,7 +66,7 @@ pub fn run() -> Result<(), Error> {
         pragma journal_mode = wal;
         pragma page_size = 16384;
     "#)?;
-    db::Database::init(&mut conn)?;
+    db::init(&mut conn)?;
     info!("Database initialized.");
     Ok(())
 }
diff --git a/src/cmds/run.rs b/src/cmds/run.rs
index 651ba11..3b5f96f 100644
--- a/src/cmds/run.rs
+++ b/src/cmds/run.rs
@@ -96,7 +96,7 @@ struct Syncer {
 
 pub fn run() -> Result<(), Error> {
     let args: Args = super::parse_args(USAGE)?;
-    let clocks = Arc::new(clock::RealClocks{});
+    let clocks = clock::RealClocks {};
     let (_db_dir, conn) = super::open_conn(
         &args.flag_db_dir,
         if args.flag_read_only { super::OpenMode::ReadOnly } else { super::OpenMode::ReadWrite })?;
@@ -123,7 +123,6 @@ pub fn run() -> Result<(), Error> {
         let streams = l.streams_by_id().len();
         let env = streamer::Environment {
             db: &db,
-            clocks: clocks.clone(),
             opener: &*stream::FFMPEG,
             shutdown: &shutdown_streamers,
         };
diff --git a/src/mp4.rs b/src/mp4.rs
index 71845f9..85cc8ef 100644
--- a/src/mp4.rs
+++ b/src/mp4.rs
@@ -1518,6 +1518,7 @@ impl http_serve::Entity for File {
 #[cfg(test)]
 mod tests {
     use byteorder::{BigEndian, ByteOrder};
+    use clock::RealClocks;
     use db::recording::{self, TIME_UNITS_PER_SEC};
     use db::testutil::{self, TestDb, TEST_STREAM_ID};
     use db::writer;
@@ -1745,7 +1746,7 @@ mod tests {
         }
     }
 
-    fn copy_mp4_to_db(db: &TestDb) {
+    fn copy_mp4_to_db(db: &TestDb<RealClocks>) {
         let mut input =
             stream::FFMPEG.open(stream::Source::File("src/testdata/clip.mp4")).unwrap();
 
@@ -1756,8 +1757,7 @@ mod tests {
             extra_data.width, extra_data.height, extra_data.sample_entry,
             extra_data.rfc6381_codec).unwrap();
         let dir = db.dirs_by_stream_id.get(&TEST_STREAM_ID).unwrap();
-        let mut output = writer::Writer::new(&::base::clock::RealClocks{}, dir, &db.db,
-                                             &db.syncer_channel, TEST_STREAM_ID,
+        let mut output = writer::Writer::new(dir, &db.db, &db.syncer_channel, TEST_STREAM_ID,
                                              video_sample_entry_id);
 
         // end_pts is the pts of the end of the most recent frame (start + duration).
@@ -1785,7 +1785,7 @@ mod tests {
         db.syncer_channel.flush();
     }
 
-    pub fn create_mp4_from_db(tdb: &TestDb,
+    pub fn create_mp4_from_db(tdb: &TestDb<RealClocks>,
                               skip_90k: i32, shorten_90k: i32, include_subtitles: bool) -> File {
         let mut builder = FileBuilder::new(Type::Normal);
         builder.include_timestamp_subtitle_track(include_subtitles);
@@ -1858,7 +1858,7 @@ mod tests {
 
     /// Makes a `.mp4` file which is only good for exercising the `Slice` logic for producing
     /// sample tables that match the supplied encoder.
-    fn make_mp4_from_encoders(type_: Type, db: &TestDb,
+    fn make_mp4_from_encoders(type_: Type, db: &TestDb<RealClocks>,
                               mut recordings: Vec<db::RecordingToInsert>,
                               desired_range_90k: Range<i32>) -> File {
         let mut builder = FileBuilder::new(type_);
@@ -1879,7 +1879,7 @@ mod tests {
     #[test]
     fn test_all_sync_frames() {
         testutil::init();
-        let db = TestDb::new();
+        let db = TestDb::new(RealClocks {});
         let mut r = db::RecordingToInsert::default();
         let mut encoder = recording::SampleIndexEncoder::new();
         for i in 1..6 {
@@ -1933,7 +1933,7 @@ mod tests {
     #[test]
     fn test_half_sync_frames() {
         testutil::init();
-        let db = TestDb::new();
+        let db = TestDb::new(RealClocks {});
         let mut r = db::RecordingToInsert::default();
         let mut encoder = recording::SampleIndexEncoder::new();
         for i in 1..6 {
@@ -1996,7 +1996,7 @@ mod tests {
     #[test]
     fn test_multi_segment() {
         testutil::init();
-        let db = TestDb::new();
+        let db = TestDb::new(RealClocks {});
         let mut encoders = Vec::new();
         let mut r = db::RecordingToInsert::default();
         let mut encoder = recording::SampleIndexEncoder::new();
@@ -2033,7 +2033,7 @@ mod tests {
     #[test]
     fn test_zero_duration_recording() {
         testutil::init();
-        let db = TestDb::new();
+        let db = TestDb::new(RealClocks {});
         let mut encoders = Vec::new();
         let mut r = db::RecordingToInsert::default();
         let mut encoder = recording::SampleIndexEncoder::new();
@@ -2059,7 +2059,7 @@ mod tests {
     #[test]
     fn test_media_segment() {
         testutil::init();
-        let db = TestDb::new();
+        let db = TestDb::new(RealClocks {});
         let mut r = db::RecordingToInsert::default();
         let mut encoder = recording::SampleIndexEncoder::new();
         for i in 1..6 {
@@ -2102,7 +2102,7 @@ mod tests {
     #[test]
     fn test_round_trip() {
         testutil::init();
-        let db = TestDb::new();
+        let db = TestDb::new(RealClocks {});
         copy_mp4_to_db(&db);
         let mp4 = create_mp4_from_db(&db, 0, 0, false);
         let new_filename = write_mp4(&mp4, db.tmpdir.path());
@@ -2123,7 +2123,7 @@ mod tests {
     #[test]
     fn test_round_trip_with_subtitles() {
         testutil::init();
-        let db = TestDb::new();
+        let db = TestDb::new(RealClocks {});
         copy_mp4_to_db(&db);
         let mp4 = create_mp4_from_db(&db, 0, 0, true);
         let new_filename = write_mp4(&mp4, db.tmpdir.path());
@@ -2144,7 +2144,7 @@ mod tests {
     #[test]
     fn test_round_trip_with_edit_list() {
         testutil::init();
-        let db = TestDb::new();
+        let db = TestDb::new(RealClocks {});
         copy_mp4_to_db(&db);
         let mp4 = create_mp4_from_db(&db, 1, 0, false);
         let new_filename = write_mp4(&mp4, db.tmpdir.path());
@@ -2165,7 +2165,7 @@ mod tests {
     #[test]
     fn test_round_trip_with_shorten() {
         testutil::init();
-        let db = TestDb::new();
+        let db = TestDb::new(RealClocks {});
         copy_mp4_to_db(&db);
         let mp4 = create_mp4_from_db(&db, 0, 1, false);
         let new_filename = write_mp4(&mp4, db.tmpdir.path());
@@ -2214,7 +2214,7 @@ mod bench {
 
     impl BenchServer {
         fn new() -> BenchServer {
-            let db = TestDb::new();
+            let db = TestDb::new(RealClocks {});
             testutil::add_dummy_recordings_to_db(&db.db, 60);
             let mp4 = create_mp4_from_db(&db, 0, 0, false);
             let p = mp4.0.initial_sample_byte_pos;
@@ -2256,7 +2256,7 @@ mod bench {
     #[bench]
     fn build_index(b: &mut Bencher) {
         testutil::init();
-        let db = TestDb::new();
+        let db = TestDb::new(RealClocks {});
         testutil::add_dummy_recordings_to_db(&db.db, 1);
 
         let db = db.db.lock();
@@ -2307,7 +2307,7 @@ mod bench {
     #[bench]
     fn mp4_construction(b: &mut Bencher) {
         testutil::init();
-        let db = TestDb::new();
+        let db = TestDb::new(RealClocks {});
         testutil::add_dummy_recordings_to_db(&db.db, 60);
         b.iter(|| {
             create_mp4_from_db(&db, 0, 0, false);
diff --git a/src/streamer.rs b/src/streamer.rs
index a532e8b..9a51abf 100644
--- a/src/streamer.rs
+++ b/src/streamer.rs
@@ -41,23 +41,21 @@ use time;
 pub static ROTATE_INTERVAL_SEC: i64 = 60;
 
 /// Common state that can be used by multiple `Streamer` instances.
-pub struct Environment<'a, 'b, C, S> where C: 'a + Clocks, S: 'a + stream::Stream {
-    pub clocks: Arc<C>,
+pub struct Environment<'a, 'b, C, S> where C: Clocks + Clone, S: 'a + stream::Stream {
     pub opener: &'a stream::Opener<S>,
-    pub db: &'b Arc<Database>,
+    pub db: &'b Arc<Database<C>>,
     pub shutdown: &'b Arc<AtomicBool>,
 }
 
-pub struct Streamer<'a, C, S> where C: Clocks, S: 'a + stream::Stream {
+pub struct Streamer<'a, C, S> where C: Clocks + Clone, S: 'a + stream::Stream {
     shutdown: Arc<AtomicBool>,
 
     // State below is only used by the thread in Run.
     rotate_offset_sec: i64,
     rotate_interval_sec: i64,
-    db: Arc<Database>,
+    db: Arc<Database<C>>,
     dir: Arc<dir::SampleFileDir>,
     syncer_channel: writer::SyncerChannel<::std::fs::File>,
-    clocks: Arc<C>,
     opener: &'a stream::Opener<S>,
     stream_id: i32,
     short_name: String,
@@ -65,7 +63,7 @@ pub struct Streamer<'a, C, S> where C: Clocks, S: 'a + stream::Stream {
     redacted_url: String,
 }
 
-impl<'a, C, S> Streamer<'a, C, S> where C: 'a + Clocks, S: 'a + stream::Stream {
+impl<'a, C, S> Streamer<'a, C, S> where C: 'a + Clocks + Clone, S: 'a + stream::Stream {
     pub fn new<'b>(env: &Environment<'a, 'b, C, S>, dir: Arc<dir::SampleFileDir>,
                    syncer_channel: writer::SyncerChannel<::std::fs::File>,
                    stream_id: i32, c: &Camera, s: &Stream, rotate_offset_sec: i64,
@@ -77,7 +75,6 @@ impl<'a, C, S> Streamer<'a, C, S> where C: 'a + Clocks, S: 'a + stream::Stream {
             db: env.db.clone(),
             dir,
             syncer_channel: syncer_channel,
-            clocks: env.clocks.clone(),
             opener: env.opener,
             stream_id: stream_id,
             short_name: format!("{}-{}", c.short_name, s.type_.as_str()),
@@ -93,7 +90,7 @@ impl<'a, C, S> Streamer<'a, C, S> where C: 'a + Clocks, S: 'a + stream::Stream {
             if let Err(e) = self.run_once() {
                 let sleep_time = time::Duration::seconds(1);
                 warn!("{}: sleeping for {:?} after error: {:?}", self.short_name, sleep_time, e);
-                self.clocks.sleep(sleep_time);
+                self.db.clocks().sleep(sleep_time);
             }
         }
         info!("{}: shutting down", self.short_name);
@@ -101,16 +98,17 @@ impl<'a, C, S> Streamer<'a, C, S> where C: 'a + Clocks, S: 'a + stream::Stream {
 
     fn run_once(&mut self) -> Result<(), Error> {
         info!("{}: Opening input: {}", self.short_name, self.redacted_url);
+        let clocks = self.db.clocks();
 
         let mut stream = {
-            let _t = TimerGuard::new(&*self.clocks, || format!("opening {}", self.redacted_url));
+            let _t = TimerGuard::new(&clocks, || format!("opening {}", self.redacted_url));
             self.opener.open(stream::Source::Rtsp(&self.url))?
         };
-        let realtime_offset = self.clocks.realtime() - self.clocks.monotonic();
+        let realtime_offset = self.db.clocks().realtime() - clocks.monotonic();
         // TODO: verify width/height.
         let extra_data = stream.get_extra_data()?;
         let video_sample_entry_id = {
-            let _t = TimerGuard::new(&*self.clocks, || "inserting video sample entry");
+            let _t = TimerGuard::new(&clocks, || "inserting video sample entry");
             self.db.lock().insert_video_sample_entry(extra_data.width, extra_data.height,
                                                      extra_data.sample_entry,
                                                      extra_data.rfc6381_codec)?
@@ -121,11 +119,11 @@ impl<'a, C, S> Streamer<'a, C, S> where C: 'a + Clocks, S: 'a + stream::Stream {
         // Seconds since epoch at which to next rotate.
         let mut rotate: Option<i64> = None;
         let mut transformed = Vec::new();
-        let mut w = writer::Writer::new(&*self.clocks, &self.dir, &self.db, &self.syncer_channel,
-                                        self.stream_id, video_sample_entry_id);
+        let mut w = writer::Writer::new(&self.dir, &self.db, &self.syncer_channel, self.stream_id,
+                                        video_sample_entry_id);
         while !self.shutdown.load(Ordering::SeqCst) {
             let pkt = {
-                let _t = TimerGuard::new(&*self.clocks, || "getting next packet");
+                let _t = TimerGuard::new(&clocks, || "getting next packet");
                 stream.get_next()?
             };
             let pts = pkt.pts().ok_or_else(|| format_err!("packet with no pts"))?;
@@ -135,12 +133,12 @@ impl<'a, C, S> Streamer<'a, C, S> where C: 'a + Clocks, S: 'a + stream::Stream {
                 debug!("{}: have first key frame", self.short_name);
                 seen_key_frame = true;
             }
-            let frame_realtime = self.clocks.monotonic() + realtime_offset;
+            let frame_realtime = clocks.monotonic() + realtime_offset;
             let local_time = recording::Time::new(frame_realtime);
             rotate = if let Some(r) = rotate {
                 if frame_realtime.sec > r && pkt.is_key() {
                     trace!("{}: write on normal rotation", self.short_name);
-                    let _t = TimerGuard::new(&*self.clocks, || "closing writer");
+                    let _t = TimerGuard::new(&clocks, || "closing writer");
                     w.close(Some(pts));
                     None
                 } else {
@@ -159,7 +157,7 @@ impl<'a, C, S> Streamer<'a, C, S> where C: 'a + Clocks, S: 'a + stream::Stream {
                     // usual.  This ensures there's plenty of frame times to use when calculating
                     // the start time.
                     let r = r + if w.previously_opened()? { 0 } else { self.rotate_interval_sec };
-                    let _t = TimerGuard::new(&*self.clocks, || "creating writer");
+                    let _t = TimerGuard::new(&clocks, || "creating writer");
                     r
                 },
             };
@@ -173,13 +171,13 @@ impl<'a, C, S> Streamer<'a, C, S> where C: 'a + Clocks, S: 'a + stream::Stream {
             } else {
                 orig_data
             };
-            let _t = TimerGuard::new(&*self.clocks,
+            let _t = TimerGuard::new(&clocks,
                                       || format!("writing {} bytes", transformed_data.len()));
             w.write(transformed_data, local_time, pts, pkt.is_key())?;
             rotate = Some(r);
         }
         if rotate.is_some() {
-            let _t = TimerGuard::new(&*self.clocks, || "closing writer");
+            let _t = TimerGuard::new(&clocks, || "closing writer");
             w.close(None);
         }
         Ok(())
@@ -322,7 +320,7 @@ mod tests {
     fn basic() {
         testutil::init();
         // 2015-04-25 00:00:00 UTC
-        let clocks = Arc::new(clock::SimulatedClocks::new(time::Timespec::new(1429920000, 0)));
+        let clocks = clock::SimulatedClocks::new(time::Timespec::new(1429920000, 0));
         clocks.sleep(time::Duration::seconds(86400));  // to 2015-04-26 00:00:00 UTC
 
         let stream = stream::FFMPEG.open(stream::Source::File("src/testdata/clip.mp4")).unwrap();
@@ -335,9 +333,8 @@ mod tests {
             streams: Mutex::new(vec![stream]),
             shutdown: Arc::new(AtomicBool::new(false)),
         };
-        let db = testutil::TestDb::new();
-        let env = super::Environment{
-            clocks: Arc::clone(&clocks),
+        let db = testutil::TestDb::new(clocks.clone());
+        let env = super::Environment {
             opener: &opener,
             db: &db.db,
             shutdown: &opener.shutdown,