Bug 342532

Description Gábor Nagy 2011-04-12 05:56:53 EDT

Build Identifier: 

DBAdapter validates a table by doing a full query and relies on SQLExceptions to see if a table has already been created.

On most databases this isn't a problem, because they have server-side cursors. H2, on the other hand reads the entire table (tested with H2 1.1), which is quite an expensive operation if table has many rows. H2 reads the whole table into memory which can result in extensive swapping.

Please consider overriding validateTable() in H2Adapter as so:

@Override
protected void validateTable(IDBTable table, Statement statement) throws DBException {
	String sql = null;
    try {
    	StringBuilder builder = new StringBuilder();
    	builder.append("SELECT ");
    	appendFieldNames(builder, table);
    	builder.append(" FROM ");
    	builder.append(table);
    	builder.append(" LIMIT 1"); // Only retrieve the first result
    	sql = builder.toString();

    	ResultSet resultSet = statement.executeQuery(sql);
    	ResultSetMetaData metaData = resultSet.getMetaData();
    	int columnCount = metaData.getColumnCount();
    	if (columnCount != table.getFieldCount()) {
    		throw new DBException("DBTable " + table + " has " + columnCount + " columns instead of " + table.getFieldCount());
    	}
    } catch (SQLException ex) {
    	throw new DBException("Problem with table " + table, ex, sql);
    }
}

... or another similar solution that duplicates less code.


Reproducible: Always