Fix for SQLite3::BusyException: database is locked during parallel platform sync

.gitignore

@@ -1,4 +1,6 @@
 .env
 /coverage
 db/scopes.db
+db/scopes.db-wal
+db/scopes.db-shm
 spec/examples.txt

lib/scopes_extractor/database.rb

@@ -7,7 +7,8 @@ def connect
         database_path = resolve_database_path
         ensure_db_directory(database_path)
 
-        ScopesExtractor.db = Sequel.sqlite(database_path)
+        ScopesExtractor.db = Sequel.sqlite(database_path, timeout: 10_000,
+                                                          after_connect: method(:configure_concurrency))
         ScopesExtractor.logger.info "Connected to database: #{database_path}".green
 
         ScopesExtractor.db
@@ -50,6 +51,15 @@ def reset
 
       private
 
+      # Applied to every connection in Sequel's pool via :after_connect.
+      # +conn+ is the raw SQLite3::Database driver connection, so use #execute.
+      # WAL persists in the DB header (one writer, non-blocking readers);
+      # synchronous = NORMAL is per-connection and must be set on each one.
+      def configure_concurrency(conn)
+        conn.execute('PRAGMA journal_mode = WAL')
+        conn.execute('PRAGMA synchronous = NORMAL')
+      end
+
       def resolve_database_path
         path = Config.database_path
         path.start_with?('/') ? path : File.join(ScopesExtractor.root, path)

spec/scopes_extractor/database_spec.rb

@@ -12,7 +12,10 @@
   end
 
   after do
-    FileUtils.rm_f(test_db_path)
+    ScopesExtractor.db&.disconnect
+    ScopesExtractor.db = nil
+    # WAL mode leaves -wal/-shm side-files alongside the main database file.
+    FileUtils.rm_f([test_db_path, "#{test_db_path}-wal", "#{test_db_path}-shm"])
   end
 
   describe '.connect' do
@@ -31,6 +34,28 @@
       expect(ScopesExtractor.logger).to receive(:info).with(/Connected to database/)
       described_class.connect
     end
+
+    it 'enables WAL journal mode for concurrent access' do
+      db = described_class.connect
+      expect(db['PRAGMA journal_mode'].first[:journal_mode]).to eq('wal')
+    end
+
+    it 'sets synchronous to NORMAL on every pooled connection' do
+      db = described_class.connect
+
+      # NORMAL = 1, and it is a per-connection pragma, so exercise several
+      # concurrent connections to ensure after_connect ran on each.
+      results = Array.new(5).map do
+        Thread.new { db['PRAGMA synchronous'].first[:synchronous] }.value
+      end
+
+      expect(results).to all(eq(1))
+    end
+
+    it 'raises the busy timeout above the 5s default' do
+      db = described_class.connect
+      expect(db['PRAGMA busy_timeout'].first[:timeout]).to eq(10_000)
+    end
   end
 
   describe '.migrate' do