fix(sqlite): Design a new schema to get faster insertions.

crates/matrix-sdk-sqlite/migrations/event_cache_store/006_events.sql

@@ -0,0 +1,67 @@
+DROP INDEX "linked_chunks_id_and_room_id";
+DROP INDEX "linked_chunks_event_id_and_room_id";
+DROP TABLE "events";
+DROP TABLE "gaps";
+DROP TABLE "linked_chunks";
+
+CREATE TABLE "linked_chunks" (
+    -- Which room does this chunk belong to? (hashed key shared with the two other tables)
+    "room_id" BLOB NOT NULL,
+    -- Identifier of the chunk, unique per room. Corresponds to a `ChunkIdentifier`.
+    "id" INTEGER NOT NULL,
+
+    -- Previous chunk in the linked list. Corresponds to a `ChunkIdentifier`.
+    "previous" INTEGER,
+    -- Next chunk in the linked list. Corresponds to a `ChunkIdentifier`.
+    "next" INTEGER,
+    -- Type of underlying entries: E for events, G for gaps
+    "type" TEXT CHECK("type" IN ('E', 'G')) NOT NULL,
+
+    -- Primary key is composed of the room ID and the chunk identifier.
+    -- Such pairs must be unique.
+    PRIMARY KEY (room_id, id)
+)
+WITHOUT ROWID;
+
+CREATE TABLE "gaps" (
+    -- Which room does this event belong to? (hashed key shared with linked_chunks)
+    "room_id" BLOB NOT NULL,
+    -- Which chunk does this gap refer to? Corresponds to a `ChunkIdentifier`.
+    "chunk_id" INTEGER NOT NULL,
+
+    -- The previous batch token of a gap (encrypted value).
+    "prev_token" BLOB NOT NULL,
+
+    -- Primary key is composed of the room ID and the chunk identifier.
+    -- Such pairs must be unique.
+    PRIMARY KEY (room_id, chunk_id),
+
+    -- If the owning chunk gets deleted, delete the entry too.
+    FOREIGN KEY (chunk_id, room_id) REFERENCES linked_chunks(id, room_id) ON DELETE CASCADE
+)
+WITHOUT ROWID;
+
+-- Items for an event chunk.
+CREATE TABLE "events" (
+    -- Which room does this event belong to? (hashed key shared with linked_chunks)
+    "room_id" BLOB NOT NULL,
+    -- Which chunk does this event refer to? Corresponds to a `ChunkIdentifier`.
+    "chunk_id" INTEGER NOT NULL,
+
+    -- `OwnedEventId` for events, can be null if malformed.
+    "event_id" TEXT,
+    -- JSON serialized `TimelineEvent` (encrypted value).
+    "content" BLOB NOT NULL,
+    -- Position (index) in the chunk.
+    "position" INTEGER NOT NULL,
+
+    -- Primary key cannot be the event ID because it can be null. However, we
+    -- can use the room ID, chunk ID and position to get a nice unique value.
+    PRIMARY KEY (room_id, chunk_id, position),
+
+    -- If the owning chunk gets deleted, delete the entry too.
+    FOREIGN KEY (room_id, chunk_id) REFERENCES linked_chunks(room_id, id) ON DELETE CASCADE
+)
+WITHOUT ROWID;
+
+CREATE UNIQUE INDEX "events_event_id_and_room_id" ON events (room_id, event_id);

crates/matrix-sdk-sqlite/src/event_cache_store.rs

@@ -64,7 +64,7 @@ mod keys {
 /// This is used to figure whether the SQLite database requires a migration.
 /// Every new SQL migration should imply a bump of this number, and changes in
 /// the [`run_migrations`] function.
-const DATABASE_VERSION: u8 = 5;
+const DATABASE_VERSION: u8 = 6;
 
 /// The string used to identify a chunk of type events, in the `type` field in
 /// the database.
@@ -351,6 +351,14 @@ async fn run_migrations(conn: &SqliteAsyncConn, version: u8) -> Result<()> {
         .await?;
     }
 
+    if version < 6 {
+        conn.with_transaction(|txn| {
+            txn.execute_batch(include_str!("../migrations/event_cache_store/006_events.sql"))?;
+            txn.set_db_version(6)
+        })
+        .await?;
+    }
+
     Ok(())
 }