fastest way to iterate through large table using jdbc
November 13th, 2020

What's the best way to iterate through the table to update a column in each row?                 finally Instead you'd write your query to work on a set of data from a table rather than "looping" through the table. In this tutorial, we're going to take a deeper look at the ResultSet API. If, instead, the driver went directly to result column 23, a significant amount of processing would be saved. For example: In this example, an application uses the getTables method to determine if the WSTable table exists. Although more database CPU cycles are involved by using batches, performance is gained through the reduction of network roundtrips. The guidelines in this section will help you to manage connections and updates to improve system performance for your JDBC applications. When the addBatch method is used to consolidate 100 Insert operations, as demonstrated in Case 2, only two network roundtrips are required - one to prepare the statement and another to execute the batch. One simple solution is to set the fetchSize attribute in ResultSet to an appropriate value.                 { Optimize application-to-driver interaction. Under similar circumstances without statement pooling, use the Statement object. 3. In general, do not write code that relies on the number of result rows from a query because drivers must fetch all rows in a result set to know how many rows the query will return. Although using transactions can help application performance, do not take this tip too far. Map interface didn’t extend a Collection interface and hence it will not have its own iterator. THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS OF TECHDIVE.IN ''AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. If the user does want to see these result items, the application can query the database again, specifying only the long columns in the Select list. Compared to other JDBC methods, database metadata methods that generate ResultSet objects are relatively slow. Insensitive cursors used by JDBC drivers are ideal for applications that require high levels of concurrency on the database server and require the ability to scroll forwards and backwards through result sets.                         { The database server must flush back to disk every data page that contains updated or new data. In the following code fragment, the value of the Age column of the ResultSet object rs is retrieved using the method getInt, and the method updateInt is used to update the column with an int value of 25. To somewhat complicate this discussion, let us consider a DBMS server that does not natively support preparing a SQL statement. When using prepared statement pooling, if a query will only be executed once, use the Statement object. import java.sql.ResultSet; public HugeResultSet() )", "Case 2: With Setting Fetch Size value ->". You can use another "trick". In this case, 101 network roundtrips are required to perform 100 Insert operations: one roundtrip to prepare the statement and 100 additional roundtrips to execute its iterations. For this situation, Case 2 still outperforms Case 1. Applications that are designed as separate entities should pass the established connection object to the data collection routine instead of establishing a second connection. Each request from the application for a result row directs the JDBC driver to look up the key value for the appropriate row in its local cache, construct an optimized query that contains a Where clause similar to WHERE ROWID=?, execute the modified query, and retrieve the single result row from the server. If it is a batch process (one instance at a time), then it's bearable. Because database metadata methods are slow, invoke them in your applications as efficiently as possible. Before executing the following example, make sure you have the following in place − To execute the following example you can replace the username and password with … Our role in helping Sun Microsystems, Inc write the original JDBC standard and subsequent modifications gives us unique technical insight into JDBC application performance. However, forward-only cursors cannot be used when the rows to return are not sequential. Connection and statement handling should be addressed before implementation. Another bad practice is to connect and disconnect several times throughout your application to perform SQL statements. If the row must be located, the server usually has an internal pointer to the row available (for example, ROWID). Avoid using the getColumns method to determine characteristics about a table. In most cases, the first request to an insensitive cursor fetches all the rows and stores them on the client. This is because the JDBC driver must perform extra processing to determine the type of the value being retrieved and generate the appropriate mapping.

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