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CHAPTER 5 STATEMENT AND PREPAREDSTATEMENT
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Table 5-3. Steps in the for Loop When the Batch Size is 2 While Executing the TestUpdateBatching Class
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Loop Index Value (Value of i )
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The batch size is 2. The statement gets queued up. Since this is a new statement with a batch size of 2, it also gets queued up. This is the second insert, which implies we have reached the batch size limit. The JDBC driver sends both inserts inserting two rows, with column values of 0 and 1 for column x in table t1. This is the second delete, which implies we have reached the batch size limit. The JDBC driver sends and executes both deletes. The first delete deletes the value of a row with a column value of 1. The second delete does not delete any rows since no rows match the criteria. Hence, we are left with just one row with a value of 0 for column x.
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The key thing to note is that the delete statements in the loop directly affect the values inserted by the insert statement. In the case of a batch size of 1, the deletes worked on the data available after the inserts had been applied to the database. In the case of a batch size of 2, the state of the database on which deletes worked was different (since all deletes were sent after the two inserts were executed, not just the preceding ones). Since in the case of Oracle update batching this happens implicitly, it looks more confusing. From this discussion, we can conclude that the batch size can impact the results when we mix different statements where the following statements affect the results of the preceding ones. In such cases, we should either ensure that our logic does not get impacted by the batch size or avoid using batches altogether. For example, we can change the loop structure of the program TestUpdateBatching to the following to get consistent results (assuming we want all inserts applied before all deletes): for( int i = 0; i < 2; i++ ) { ipstmt.setInt(1, i ); int numOfRowsInserted = ipstmt.executeUpdate(); System.out.println("num of rows inserted: " + numOfRowsInserted ); } ipstmt.sendBatch(); for( int i = 0; i < 2; i++ ) { dpstmt.setInt(1, i+1 ); int numOfRowsDeleted = dpstmt.executeUpdate(); System.out.println("num of rows Deleted: " + numOfRowsDeleted ); } dpstmt.sendBatch(); conn.commit();
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CHAPTER 5 STATEMENT AND PREPAREDSTATEMENT
Oracle Update Batching vs. Standard Update Batching
In Oracle update batching, as soon as the number of statements added to the batch reaches the batch value, the batch is executed. Recall that You can set a default batch at the Connection object level, which applies to any prepared statement executed using that connection. You can set a statement batch value for any individual prepared statement. This value overrides any batch value set at the Connection object level. You can explicitly execute a batch at any time, overriding both the connection batch value and the statement batch value. In contrast to Oracle update batching, standard update batching involves an explicit manual execution of the batch, as there is no batch value. You should choose standard update batching if you are concerned about the portability of your Java code across databases. Otherwise, choose Oracle update batching because you get better performance out of it (as you ll learn in the next section).
Caution You can t mix and match the standard update batching syntax and Oracle update batching
syntax. If you do so, you will get a SQLException.
Batching Performance Analysis
The following StandardVsOracleBatching class compares the elapsed time and the latches consumed for inserting 10,000 records for the case of standard update batching and Oracle update batching. The StandardVsOracleBatching class uses the utility class (discussed in the section JDBC Wrapper for RUNSTATS of 1) to compare the latches consumed and the time taken for the preceding three cases. After the imports, the class begins by declaring some private variables: /* This program compares standard update batching with Oracle update batching for elapsed times and latches consumed using the JRunstats utility. * COMPATIBLITY NOTE: runs successfully against 10.1.0.2.0. and 9.2.0.1.0. */ import java.sql.SQLException; import java.sql.Connection; import java.sql.PreparedStatement; import oracle.jdbc.OraclePreparedStatement; import book.util.JDBCUtil; import book.util.JRunstats; class StandardVsOracleBatching { private static int s_numberOfRecords = 0;
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