diff -r a076e89a2879 -r d21a7cf8fa9e src/luan/modules/lucene/PostgresBackup.java
--- a/src/luan/modules/lucene/PostgresBackup.java	Sun Nov 24 18:23:57 2019 -0700
+++ b/src/luan/modules/lucene/PostgresBackup.java	Sun Nov 24 21:02:38 2019 -0700
@@ -200,6 +200,15 @@
 		Checker() throws SQLException {
 			con = newConnection();
 			con.setAutoCommit(false);
+			con.setReadOnly(true);
+			con.setTransactionIsolation(Connection.TRANSACTION_SERIALIZABLE);
+
+			// hack to capture data in transaction
+			Statement stmt = con.createStatement();
+			ResultSet rs = stmt.executeQuery("select 'x' from lucene");
+			while(rs.next());
+			stmt.close();
+
 			pstmt = con.prepareStatement(
 				"select data from lucene where id=?"
 			);