diff --git a/blahd/docs/webapi.yaml b/blahd/docs/webapi.yaml
index 81f8383..6788f65 100644
--- a/blahd/docs/webapi.yaml
+++ b/blahd/docs/webapi.yaml
@@ -179,7 +179,7 @@ paths:
         200:
           content:
             application/json:
-              type: integer
+              type: string
               description: Created chat id (cid).
         400:
           description: Body is invalid or fails the verification.
diff --git a/blahd/schema.sql b/blahd/schema.sql
index 7ebc5cf..9fe5ea0 100644
--- a/blahd/schema.sql
+++ b/blahd/schema.sql
@@ -23,7 +23,7 @@ CREATE TABLE IF NOT EXISTS `room_member` (
 CREATE INDEX IF NOT EXISTS `member_room` ON `room_member` (`uid` ASC, `rid` ASC);
 
 CREATE TABLE IF NOT EXISTS `room_item` (
-    `cid`       INTEGER NOT NULL PRIMARY KEY AUTOINCREMENT,
+    `cid`       INTEGER NOT NULL PRIMARY KEY,
     `rid`       INTEGER NOT NULL REFERENCES `room` ON DELETE CASCADE,
     `uid`       INTEGER NOT NULL REFERENCES `user` ON DELETE RESTRICT,
     `timestamp` INTEGER NOT NULL,
diff --git a/blahd/src/database.rs b/blahd/src/database.rs
index 8c646ae..40a6c6d 100644
--- a/blahd/src/database.rs
+++ b/blahd/src/database.rs
@@ -10,7 +10,7 @@ static INIT_SQL: &str = include_str!("../schema.sql");
 
 // Simple and stupid version check for now.
 // `echo -n 'blahd-database-0' | sha256sum | head -c5` || version
-const APPLICATION_ID: i32 = 0xd9e_8401;
+const APPLICATION_ID: i32 = 0xd9e_8402;
 
 #[derive(Debug)]
 pub struct Database {
diff --git a/blahd/src/id.rs b/blahd/src/id.rs
new file mode 100644
index 0000000..8618711
--- /dev/null
+++ b/blahd/src/id.rs
@@ -0,0 +1,21 @@
+/// Id generation.
+/// Ref: https://en.wikipedia.org/wiki/Snowflake_ID
+/// FIXME: Currently we assume no more than one request in a single millisecond.
+use std::time::SystemTime;
+
+use blah::types::Id;
+
+pub trait IdExt {
+    fn gen() -> Self;
+}
+
+impl IdExt for Id {
+    fn gen() -> Self {
+        let timestamp = SystemTime::now()
+            .duration_since(SystemTime::UNIX_EPOCH)
+            .expect("after UNIX epoch");
+        let timestamp_ms = timestamp.as_millis() as i64;
+        assert!(timestamp_ms > 0);
+        Id(timestamp_ms << 16)
+    }
+}
diff --git a/blahd/src/main.rs b/blahd/src/main.rs
index 97bc3aa..f17a892 100644
--- a/blahd/src/main.rs
+++ b/blahd/src/main.rs
@@ -18,6 +18,7 @@ use blah::types::{
 use config::Config;
 use database::Database;
 use ed25519_dalek::SIGNATURE_LENGTH;
+use id::IdExt;
 use middleware::{ApiError, MaybeAuth, ResultExt as _, SignedJson};
 use parking_lot::Mutex;
 use rusqlite::{named_params, params, Connection, OptionalExtension, Row, ToSql};
@@ -30,6 +31,7 @@ mod middleware;
 mod config;
 mod database;
 mod event;
+mod id;
 mod utils;
 
 /// Blah Chat Server
@@ -356,17 +358,18 @@ async fn room_create(
     };
 
     let txn = conn.transaction()?;
+    let rid = Id::gen();
     txn.execute(
         r"
-        INSERT INTO `room` (`title`, `attrs`)
-        VALUES (:title, :attrs)
+        INSERT INTO `room` (`rid`, `title`, `attrs`)
+        VALUES (:rid, :title, :attrs)
         ",
         named_params! {
+            ":rid": rid,
             ":title": params.signee.payload.title,
             ":attrs": params.signee.payload.attrs,
         },
     )?;
-    let rid = Id(txn.last_insert_rowid());
     let mut insert_user = txn.prepare(
         r"
         INSERT INTO `user` (`userkey`)
@@ -664,7 +667,7 @@ async fn room_post_item(
     st: ArcState,
     R(Path(rid), _): RE<Path<Id>>,
     SignedJson(chat): SignedJson<ChatPayload>,
-) -> Result<Json<u64>, ApiError> {
+) -> Result<Json<Id>, ApiError> {
     if rid != chat.signee.payload.room {
         return Err(error_response!(
             StatusCode::BAD_REQUEST,
@@ -705,13 +708,14 @@ async fn room_post_item(
             ));
         };
 
-        let cid = conn.query_row(
+        let cid = Id::gen();
+        conn.execute(
             r"
-            INSERT INTO `room_item` (`rid`, `uid`, `timestamp`, `nonce`, `sig`, `rich_text`)
-            VALUES (:rid, :uid, :timestamp, :nonce, :sig, :rich_text)
-            RETURNING `cid`
+            INSERT INTO `room_item` (`cid`, `rid`, `uid`, `timestamp`, `nonce`, `sig`, `rich_text`)
+            VALUES (:cid, :rid, :uid, :timestamp, :nonce, :sig, :rich_text)
             ",
             named_params! {
+                ":cid": cid,
                 ":rid": rid,
                 ":uid": uid,
                 ":timestamp": chat.signee.timestamp,
@@ -719,7 +723,6 @@ async fn room_post_item(
                 ":rich_text": &chat.signee.payload.rich_text,
                 ":sig": chat.sig,
             },
-            |row| row.get::<_, u64>(0),
         )?;
 
         // FIXME: Optimize this to not traverses over all members.