diff --git a/Cargo.toml b/Cargo.toml
index 3f6d558b..c622804c 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -29,6 +29,7 @@ rustc_version = "0.2"
 chrono = "0.4"
 error-chain = { git = "https://github.com/rnewman/error-chain", branch = "rnewman/sync" }
 lazy_static = "0.2"
+smallvec = "0.6"
 time = "0.1"
 uuid = "0.5"
 
diff --git a/db/Cargo.toml b/db/Cargo.toml
index 634d9d1a..ecbded5d 100644
--- a/db/Cargo.toml
+++ b/db/Cargo.toml
@@ -10,6 +10,7 @@ itertools = "0.7"
 lazy_static = "0.2"
 num = "0.1"
 ordered-float = "0.5"
+smallvec = "0.6"
 time = "0.1"
 
 [dependencies.rusqlite]
diff --git a/db/src/lib.rs b/db/src/lib.rs
index cfa6948c..debed886 100644
--- a/db/src/lib.rs
+++ b/db/src/lib.rs
@@ -21,6 +21,7 @@ extern crate lazy_static;
 
 extern crate num;
 extern crate rusqlite;
+extern crate smallvec;
 extern crate tabwriter;
 extern crate time;
 
diff --git a/db/src/tx.rs b/db/src/tx.rs
index 96fa989f..20d35bfe 100644
--- a/db/src/tx.rs
+++ b/db/src/tx.rs
@@ -671,6 +671,7 @@ impl<'conn, 'a, W> Tx<'conn, 'a, W> where W: TransactWatcher {
                     }
 
                     self.watcher.datom(op, e, a, &v);
+                    // TODO: Create something like a watcher to do this for us.
                     affected_attrs.insert(a);
 
                     let reduced = (e, a, attribute, v, added);
diff --git a/db/src/tx_observer.rs b/db/src/tx_observer.rs
index 240e9ae0..456bd51a 100644
--- a/db/src/tx_observer.rs
+++ b/db/src/tx_observer.rs
@@ -10,6 +10,13 @@
 
 use std::sync::{
     Arc,
+    Weak,
+};
+use std::sync::mpsc::{
+    channel,
+    Receiver,
+    RecvError,
+    Sender,
 };
 use std::thread;
 
@@ -17,155 +24,156 @@ use indexmap::{
     IndexMap,
 };
 
+use smallvec::{
+    SmallVec,
+};
+
 use types::{
     AttributeSet,
     TxReport,
 };
 
 pub struct TxObserver {
-    notify_fn: Arc<Option<Box<Fn(String, Vec<TxReport>) + Send + Sync>>>,
+    notify_fn: Arc<Box<Fn(&str, SmallVec<[&TxReport; 4]>) + Send + Sync>>,
     attributes: AttributeSet,
 }
 
 impl TxObserver {
-    pub fn new<F>(attributes: AttributeSet, notify_fn: F) -> TxObserver where F: Fn(String, Vec<TxReport>) + 'static + Send + Sync {
+    pub fn new<F>(attributes: AttributeSet, notify_fn: F) -> TxObserver where F: Fn(&str, SmallVec<[&TxReport; 4]>) + 'static + Send + Sync {
         TxObserver {
-            notify_fn: Arc::new(Some(Box::new(notify_fn))),
+            notify_fn: Arc::new(Box::new(notify_fn)),
             attributes,
         }
     }
 
-    pub fn applicable_reports(&self, reports: &Vec<TxReport>) -> Vec<TxReport> {
-        reports.into_iter().filter_map( |report| {
-            if self.attributes.intersection(&report.changeset).next().is_some(){
-                Some(report.clone())
-            } else {
-                None
-            }
+    pub fn applicable_reports<'r>(&self, reports: &'r SmallVec<[TxReport; 4]>) -> SmallVec<[&'r TxReport; 4]> {
+        reports.into_iter().filter_map(|report| {
+            self.attributes.intersection(&report.changeset)
+                           .next()
+                           .and_then(|_| Some(report))
         }).collect()
     }
 
-    fn notify(&self, key: String, reports: Vec<TxReport>) {
-        if let Some(ref notify_fn) = *self.notify_fn {
-            (notify_fn)(key, reports);
-        } else {
-            eprintln!("no notify function specified for TxObserver");
-        }
+    fn notify(&self, key: &str, reports: SmallVec<[&TxReport; 4]>) {
+        (*self.notify_fn)(key, reports);
     }
 }
 
-pub trait CommandClone {
-    fn clone_box(&self) -> Box<Command + Send>;
+pub trait Command {
+    fn execute(&mut self);
 }
 
-impl<T> CommandClone for T where T: 'static + Command + Clone + Send {
-    fn clone_box(&self) -> Box<Command + Send> {
-        Box::new(self.clone())
-    }
+pub struct TxCommand {
+    reports: SmallVec<[TxReport; 4]>,
+    observers: Weak<IndexMap<String, Arc<TxObserver>>>,
 }
 
-pub trait Command: CommandClone {
-    fn execute(&self);
-}
-
-impl Clone for Box<Command + Send> {
-    fn clone(&self) -> Box<Command + Send> {
-        self.clone_box()
-    }
-}
-
-#[derive(Clone)]
-pub struct NotifyTxObserver {
-    key: String,
-    reports: Vec<TxReport>,
-    observer: Arc<TxObserver>,
-}
-
-impl NotifyTxObserver {
-    pub fn new(key: String, reports: Vec<TxReport>, observer: Arc<TxObserver>) -> Self {
-        NotifyTxObserver {
-            key,
+impl TxCommand {
+    fn new(observers: &Arc<IndexMap<String, Arc<TxObserver>>>, reports: SmallVec<[TxReport; 4]>) -> Self {
+        TxCommand {
             reports,
-            observer,
+            observers: Arc::downgrade(observers),
         }
     }
 }
 
-impl Command for NotifyTxObserver {
-    fn execute(&self) {
-        self.observer.notify(self.key.clone(), self.reports.clone());
-    }
-}
-
-#[derive(Clone)]
-pub struct AsyncBatchExecutor {
-    commands: Vec<Box<Command + Send>>,
-}
-
-impl Command for AsyncBatchExecutor {
-    fn execute(&self) {
-        let command_queue = self.commands.clone();
-        thread::spawn (move ||{
-            for command in command_queue.iter() {
-                command.execute();
+impl Command for TxCommand {
+    fn execute(&mut self) {
+        self.observers.upgrade().map(|observers| {
+            for (key, observer) in observers.iter() {
+                let applicable_reports = observer.applicable_reports(&self.reports);
+                if !applicable_reports.is_empty() {
+                    observer.notify(&key, applicable_reports);
+                }
             }
         });
     }
 }
 
-#[derive(Clone)]
 pub struct TxObservationService {
-    observers: IndexMap<String, Arc<TxObserver>>,
-    pub command_queue: Vec<Box<Command + Send>>,
+    observers: Arc<IndexMap<String, Arc<TxObserver>>>,
+    executor: Option<Sender<Box<Command + Send>>>,
+    in_progress_count: i32,
 }
 
 impl TxObservationService {
     pub fn new() -> Self {
         TxObservationService {
-            observers: IndexMap::new(),
-            command_queue: Vec::new(),
+            observers: Arc::new(IndexMap::new()),
+            executor: None,
+            in_progress_count: 0,
         }
     }
+
     // For testing purposes
     pub fn is_registered(&self, key: &String) -> bool {
         self.observers.contains_key(key)
     }
 
     pub fn register(&mut self, key: String, observer: Arc<TxObserver>) {
-        self.observers.insert(key.clone(), observer);
+        Arc::make_mut(&mut self.observers).insert(key, observer);
     }
 
     pub fn deregister(&mut self, key: &String) {
-        self.observers.remove(key);
+        Arc::make_mut(&mut self.observers).remove(key);
     }
 
     pub fn has_observers(&self) -> bool {
         !self.observers.is_empty()
     }
 
-    fn command_from_reports(&self, key: &String, reports: &Vec<TxReport>, observer: &Arc<TxObserver>) -> Option<Box<Command + Send>> {
-        let applicable_reports = observer.applicable_reports(reports);
-        if !applicable_reports.is_empty() {
-            Some(Box::new(NotifyTxObserver::new(key.clone(), applicable_reports, Arc::clone(observer))))
-        } else {
-            None
-        }
+    pub fn transaction_did_start(&mut self) {
+        self.in_progress_count += 1;
     }
 
-    pub fn transaction_did_commit(&mut self, reports: Vec<TxReport>) {
-        // notify all observers about their relevant transactions
-        let commands: Vec<Box<Command + Send>> = self.observers
-                                                .iter()
-                                                .filter_map(|(key, observer)| { self.command_from_reports(&key, &reports, &observer) })
-                                                .collect();
-        self.command_queue.push(Box::new(AsyncBatchExecutor{ commands }));
-    }
+    pub fn transaction_did_commit(&mut self, reports: SmallVec<[TxReport; 4]>) {
+        {
+            let executor = self.executor.get_or_insert_with(||{
+                let (tx, rx): (Sender<Box<Command + Send>>, Receiver<Box<Command + Send>>) = channel();
+                let mut worker = CommandExecutor::new(rx);
 
-    pub fn run(&mut self) {
-        for command in self.command_queue.iter() {
-            command.execute();
+                thread::spawn(move || {
+                    worker.main();
+                });
+
+                tx
+            });
+
+            let cmd = Box::new(TxCommand::new(&self.observers, reports));
+            executor.send(cmd).unwrap();
         }
 
-        self.command_queue.clear();
+        self.in_progress_count -= 1;
+
+        if self.in_progress_count == 0 {
+            self.executor = None;
+        }
+    }
+}
+
+struct CommandExecutor {
+    reciever: Receiver<Box<Command + Send>>,
+}
+
+impl CommandExecutor {
+    fn new(rx: Receiver<Box<Command + Send>>) -> Self {
+        CommandExecutor {
+            reciever: rx,
+        }
+    }
+
+    fn main(&mut self) {
+        loop {
+            match self.reciever.recv() {
+                Err(RecvError) => {
+                    eprintln!("Disconnected, terminating CommandExecutor");
+                    return
+                },
+
+                Ok(mut cmd) => {
+                    cmd.execute()
+                },
+            }
+        }
     }
 }
diff --git a/src/conn.rs b/src/conn.rs
index a76d7772..665ea9a0 100644
--- a/src/conn.rs
+++ b/src/conn.rs
@@ -32,6 +32,8 @@ use rusqlite::{
     TransactionBehavior,
 };
 
+use smallvec::SmallVec;
+
 use edn;
 
 use mentat_core::{
@@ -214,7 +216,8 @@ pub struct InProgress<'a, 'c> {
     schema: Schema,
     cache: InProgressSQLiteAttributeCache,
     use_caching: bool,
-    tx_reports: Vec<TxReport>,
+    // TODO: Collect txids/affected datoms in a better way
+    tx_reports: SmallVec<[TxReport; 4]>,
     observer_service: Option<&'a Mutex<TxObservationService>>,
 }
 
@@ -453,12 +456,6 @@ impl<'a, 'c> InProgress<'a, 'c> {
         metadata.generation += 1;
         metadata.partition_map = self.partition_map;
 
-        // let the transaction observer know that there have been some transactions committed.
-        if let Some(ref observer_service) = self.observer_service {
-            let mut os = observer_service.lock().unwrap();
-            os.transaction_did_commit(self.tx_reports);
-        }
-
         // Update the conn's cache if we made any changes.
         self.cache.commit_to(&mut metadata.attribute_cache);
 
@@ -470,10 +467,10 @@ impl<'a, 'c> InProgress<'a, 'c> {
             // TODO: consider making vocabulary lookup lazy -- we won't need it much of the time.
         }
 
-        // run any commands that we've created along the way.
+        // let the transaction observer know that there have been some transactions committed.
         if let Some(ref observer_service) = self.observer_service {
             let mut os = observer_service.lock().unwrap();
-            os.run();
+            os.transaction_did_commit(self.tx_reports);
         }
 
         Ok(())
@@ -728,6 +725,14 @@ impl Conn {
              current.attribute_cache.clone())
         };
 
+        let mut obs = self.tx_observer_service.lock().unwrap();
+        let observer_service = if obs.has_observers() {
+            obs.transaction_did_start();
+            Some(&self.tx_observer_service)
+        } else {
+            None
+        };
+
         Ok(InProgress {
             mutex: &self.metadata,
             transaction: tx,
@@ -736,8 +741,8 @@ impl Conn {
             schema: (*current_schema).clone(),
             cache: InProgressSQLiteAttributeCache::from_cache(cache_cow),
             use_caching: true,
-            tx_reports: Vec::new(),
-            observer_service: if self.tx_observer_service.lock().unwrap().has_observers() { Some(&self.tx_observer_service) } else { None },
+            tx_reports: SmallVec::new(),
+            observer_service: observer_service,
         })
     }
 
@@ -846,7 +851,6 @@ mod tests {
         Duration,
         Instant
     };
-    use std::thread;
 
     use mentat_core::{
         CachedAttributes,
@@ -1534,16 +1538,21 @@ mod tests {
         let output = Arc::new(Mutex::new(ObserverOutput::default()));
 
         let mut_output = Arc::downgrade(&output);
+        let (tx, rx): (::std::sync::mpsc::Sender<()>, ::std::sync::mpsc::Receiver<()>) = ::std::sync::mpsc::channel();
+        // because the TxObserver is in an Arc and is therefore Sync, we have to wrap the Sender in a Mutex to also
+        // make it Sync.
+        let thread_tx = Mutex::new(tx);
         let tx_observer = Arc::new(TxObserver::new(registered_attrs, move |obs_key, batch| {
             if let Some(out) = mut_output.upgrade() {
                 let mut o = out.lock().unwrap();
-                o.called_key = Some(obs_key.clone());
+                o.called_key = Some(obs_key.to_string());
                 for report in batch.iter() {
                     o.txids.push(report.tx_id.clone());
                     o.changes.push(report.changeset.clone());
                 }
                 o.txids.sort();
             }
+            thread_tx.lock().unwrap().send(()).unwrap();
         }));
 
         conn.register_observer(key.clone(), Arc::clone(&tx_observer));
@@ -1557,7 +1566,7 @@ mod tests {
                 let name = format!("todo{}", i);
                 let uuid = Uuid::new_v4();
                 let mut builder = in_progress.builder().describe_tempid(&name);
-                builder.add_kw( &kw!(:todo/uuid), TypedValue::Uuid(uuid)).expect("Expected added uuid");
+                builder.add_kw(&kw!(:todo/uuid), TypedValue::Uuid(uuid)).expect("Expected added uuid");
                 builder.add_kw(&kw!(:todo/name), TypedValue::typed_string(&name)).expect("Expected added name");
                 if i % 2 == 0 {
                     builder.add_kw(&kw!(:todo/completion_date), TypedValue::current_instant()).expect("Expected added date");
@@ -1575,7 +1584,7 @@ mod tests {
         }
 
         let delay = Duration::from_millis(100);
-        thread::sleep(delay);
+        let _ = rx.recv_timeout(delay);
 
         match Arc::try_unwrap(output) {
             Ok(out) => {
@@ -1608,16 +1617,19 @@ mod tests {
         let output = Arc::new(Mutex::new(ObserverOutput::default()));
 
         let mut_output = Arc::downgrade(&output);
+        let (tx, rx): (::std::sync::mpsc::Sender<()>, ::std::sync::mpsc::Receiver<()>) = ::std::sync::mpsc::channel();
+        let thread_tx = Mutex::new(tx);
         let tx_observer = Arc::new(TxObserver::new(registered_attrs, move |obs_key, batch| {
             if let Some(out) = mut_output.upgrade() {
                 let mut o = out.lock().unwrap();
-                o.called_key = Some(obs_key.clone());
+                o.called_key = Some(obs_key.to_string());
                 for report in batch.iter() {
                     o.txids.push(report.tx_id.clone());
                     o.changes.push(report.changeset.clone());
                 }
                 o.txids.sort();
             }
+            thread_tx.lock().unwrap().send(()).unwrap();
         }));
 
         conn.register_observer(key.clone(), Arc::clone(&tx_observer));
@@ -1638,7 +1650,7 @@ mod tests {
         }
 
         let delay = Duration::from_millis(100);
-        thread::sleep(delay);
+        let _ = rx.recv_timeout(delay);
 
         match Arc::try_unwrap(output) {
             Ok(out) => {
diff --git a/src/lib.rs b/src/lib.rs
index d51eb60c..fdc28dff 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -18,6 +18,8 @@ extern crate lazy_static;
 
 extern crate rusqlite;
 
+extern crate smallvec;
+
 extern crate uuid;
 
 pub extern crate edn;