Question

I’m using HSQLDB. Inside a java function I’m creating a temporary table and populating it with some data. Right after I’m updating a regular table with the data from the temporary table.

If I debug the code inside the function and perform SELECT I can see that the data was indeed updated in both tables, but after committing the changes the table is no longer updated! (the regular table, not the temporary one).

When I created the temp table I used: ON COMMIT PRESERVE ROWS but it doesn’t help.

Does anyone know why is this happening?

Thanks!

Here is the code:

public synchronized void foo(String[] objectsToMark) throws Exception {

        String createTempTableQuery = "CREATE TEMP TABLE "+TEMP_TABLE_NAME+"(OBJECTID VARCHAR) " +
                "ON COMMIT PRESERVE ROWS";
        String dropTempTableQuery = "DROP TABLE "+TEMP_TABLE_NAME;

        String updateQueryString = "update " + TABlE_A + " set " +TABlE_A+".X = 'N' where "+TABlE_A+".RESULT_ID in (select "+TABlE_A+".RESULT_ID FROM "+TABlE_A
                        +" inner join "+TABLE_B+" on "+TABLE_B+".OBJECTID = "+TABlE_A+".OBJECTID"
                        +" inner join TEMP_TABLE on "+TABLE_B+".OBJECTID = TEMP_TABLE.OBJECTID"
                        +" where "+TABlE_A+".IS_X = 'Y')";

        String insertObjectIDs = "INSERT INTO " + TEMP_TABLE_NAME + " (OBJECTID) VALUES (?)";
        Connection conn = null;
        Statement stmt = null;
        PreparedStatement psInsertObjectIDs = null;
        try {
            conn = getConnection(getClass().getName() + "");
            stmt = conn.createStatement();


            stmt.execute(createTempTableQuery);

            // insert object's IDs into table
            psInsertObjectIDs = conn.prepareStatement(insertObjectIDs);

            for (String id : objectsToMark) {
                int i = 0;
                psInsertObjectIDs.setString(++i, id);
                psInsertObjectIDs.addBatch();
            }
            psInsertObjectIDs.executeBatch();

            stmt.execute(updateQueryString);

        } catch (Exception e) {
        } finally {
            // close resources
            close(stmt);
            stmt = null;
            // drop the temporary tables
            if (conn != null) {
                try {
                    stmt = conn.createStatement();
                    stmt.execute(dropTempTableQuery);
                } catch (SQLException e) {
                }
                close(stmt);
            }

            close(psInsertObjectIDs);
            closeConnection(conn);
        }
    }

Notice that there is no commit here but the connection is configured to perform auto commit.

Answer 1

As the code works when you debug, the problem must be outside this code.

If you are running this code as an isolated test on a file: database, and you have not specified a write delay or shutdown option in the jdbc connection url, then the engine does not get enough time to write the data to disk.

The default settings of HSQLDB are for production, where a SHUTDOWN is issued by the application program. For tests, use either of the properties below.

This one writes the changes after each commit or auto-commit, therefore slows down production databases:

jdbc:hsqldb:file:mydb;hsqldb.write_delay=false

This one shuts down the database when the only remaining connection is closed:

jdbc:hsqldb:file:mydb;shutdown=true

As this issue comes up quite often, future versions of HSQLDB from 2.2.9 will always write the data to disk when the only remaining connection is closed.