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// ignore any exceptions since we are in the // finally clause. JDBCUtil.close( opstmt ); JDBCUtil.close( oconn ); } } } When we execute the preceding program (after deleting any pre-existing rows from t1), we get the following output: B:\>java DemoOracleUpdateBatching ora10g URL:jdbc:oracle:thin:@(DESCRIPTION=(ADDRESS=(PROTOCOL=tcp)(PORT=1521)(HOST=rmeno n-lap))(CONNECT_DATA=(SID=ora10g))) num of rows inserted: 0 num of rows inserted: 0 num of rows inserted: 3 num of rows inserted: 0 num of rows sent for batch: 1 As expected, the first two inserts were actually queued up and sent along with the third insert, as is evident from the number of rows inserted. The next insert is, however, executed explicitly when we use the sendBatch() method. Now that you re familiar with both types of batching, next we ll cover a caveat regarding mixing interdependent statements in a batch.
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Both update batching implementations generally work as expected. There are cases where the results may be surprising to you (especially when you use Oracle update batching). Intuitively, you would expect that changing the batch size should impact only the performance of the application, not the actual data inserted, deleted, and so on. However, this is not the case if you have multiple statements using batching in a loop, and some of these statements can have an impact on the rows manipulated by other statements in the loop. Consider the following class (based on a test case supplied by Tom Kyte), which uses Oracle update batching. It takes a batch size as a command-line parameter and uses Oracle update batching to set the execution batch size on an insert and a delete from the same table t1 that we created in the earlier examples: /* This program illustrates a special case of Oracle update batching where the results are nonintuitive although correct as per the JDBC specification. * COMPATIBLITY NOTE: runs successfully against 10.1.0.2.0. and 9.2.0.1.0. */ import java.sql.Statement; import java.sql.Connection; import java.sql.PreparedStatement; import oracle.jdbc.OraclePreparedStatement; import book.util.JDBCUtil;
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class TestUpdateBatching { public static void main(String args[])throws Exception { if( args.length != 1 ) { System.out.println("Usage: java TestUpdateBatching <batch_size>" ); } int batchSize = Integer.parseInt( args[0] ); Connection conn = null; Statement stmt = null; OraclePreparedStatement ipstmt = null; OraclePreparedStatement dpstmt = null; try { conn = JDBCUtil.getConnection("benchmark", "benchmark", "ora10g"); stmt = conn.createStatement (); ipstmt = (OraclePreparedStatement) conn.prepareStatement( "insert into t1( x ) values ( )"); ipstmt.setExecuteBatch( batchSize ); dpstmt = (OraclePreparedStatement) conn.prepareStatement( "delete from t1 where x = " ); dpstmt.setExecuteBatch( batchSize ); After creating the insert and delete statements and setting their batch size, we go in a loop where the insert statement inserts the loop index i, and the delete statement deletes the values matching 1 added to the loop index (i.e., i + 1). for( int i = 0; i < 2; i++ ) { ipstmt.setInt(1, i ); int numOfRowsInserted = ipstmt.executeUpdate(); System.out.println("num of rows inserted: " + numOfRowsInserted ); dpstmt.setInt(1, i+1 ); int numOfRowsDeleted = dpstmt.executeUpdate(); System.out.println("num of rows Deleted: " + numOfRowsDeleted ); } We send the batches for any remaining rows outside and commit the transaction at the end of the program: ipstmt.sendBatch(); dpstmt.sendBatch(); conn.commit(); } catch (Exception e) { // handle the exception properly - in this case, we just // print a message and roll back JDBCUtil.printExceptionAndRollback( conn, e );
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} finally { // close the result set, statement, and connection. // ignore any exceptions since we are in the // finally clause. JDBCUtil.close( ipstmt ); JDBCUtil.close( dpstmt ); JDBCUtil.close( conn ); } } } When we run the program with a batch size of 1, we get the following output: B:\>java TestUpdateBatching 1 URL:jdbc:oracle:thin:@(DESCRIPTION=(ADDRESS=(PROTOCOL=tcp)(PORT=1521)(HOST=rmeno n-lap))(CONNECT_DATA=(SID=ora10g))) num of rows inserted: 1 num of rows Deleted: 0 num of rows inserted: 1 num of rows Deleted: 0 A select from table t1 gives benchmark@ORA10G> select * from t1; 0 1 After deleting all rows from table t1, let s run the program with a batch size of 2: B:\>java TestUpdateBatching 2 URL:jdbc:oracle:thin:@(DESCRIPTION=(ADDRESS=(PROTOCOL=tcp)(PORT=1521) (HOST=rmenon-lap))(CONNECT_DATA=(SID=ora10g))) num of rows inserted: 0 num of rows Deleted: 0 num of rows inserted: 2 num of rows Deleted: 1 When we do a select this time, we get a different result from the one we got when the batch size was 1: benchmark@ORA10G> select * from t1; 0 This is a case in which changing the batch size apparently changed the program s outcome! Although this looks like a bug, it turns out that this behavior is correct. Recall that in Oracle update batching, a batch is automatically sent to the database once the batch size is reached. When the batch size is 1, the delete statement does not affect any rows, since it attempts to delete values that do not exist in the database. So, we get two rows as expected. Table 5-3 lists the steps the JDBC driver goes through when the batch size is 2.
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