forked from cockroachdb/docs
-
Notifications
You must be signed in to change notification settings - Fork 0
Commit
This commit does not belong to any branch on this repository, and may belong to a fork outside of the repository.
Test App: Add Java code for transaction retries
Add example code for transaction retry logic. Compilation and execution instructions are in a comment in the main code file. Fixes cockroachdb#757.
- Loading branch information
Showing
3 changed files
with
95 additions
and
12 deletions.
There are no files selected for viewing
This file contains bidirectional Unicode text that may be interpreted or compiled differently than what appears below. To review, open the file in an editor that reveals hidden Unicode characters.
Learn more about bidirectional Unicode characters
| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,83 @@ | ||
| import java.sql.*; | ||
|
|
||
| /* | ||
| You can compile and run this example with a command like: | ||
| javac TxnSample.java && java -cp .:~/path/to/postgresql-9.4.1208.jar TxnSample | ||
| You can download the postgres JDBC driver jar from https://jdbc.postgresql.org. | ||
| */ | ||
|
|
||
| class InsufficientBalanceException extends Exception {} | ||
|
|
||
| // A simple interface that provides a retryable lambda expression. | ||
| interface RetryableTransaction { | ||
| public void run(Connection conn) throws Exception; | ||
| } | ||
|
|
||
| public class TxnSample { | ||
| public static RetryableTransaction transferFunds(int from, int to, int amount) { | ||
| return new RetryableTransaction() { | ||
| public void run(Connection conn) throws Exception { | ||
| ResultSet res = conn.createStatement().executeQuery("SELECT balance FROM accounts WHERE id = " + from); | ||
| res.next(); | ||
| int balance = res.getInt("balance"); | ||
| if(balance < from) { | ||
| throw new InsufficientBalanceException(); | ||
| } | ||
| conn.createStatement().executeUpdate("UPDATE accounts SET balance = balance - " + amount + " where id = " + from); | ||
| conn.createStatement().executeUpdate("UPDATE accounts SET balance = balance + " + amount + " where id = " + to); | ||
| } | ||
| }; | ||
| } | ||
|
|
||
| public static void retryTransaction(Connection conn, RetryableTransaction tx) throws Exception { | ||
| Savepoint sp = conn.setSavepoint("cockroach_restart"); | ||
| while(true) { | ||
| try { | ||
| // Attempt the transaction. | ||
| tx.run(conn); | ||
|
|
||
| // If we reach this point, commit the transaction, | ||
| // which implicitly releases the savepoint. | ||
| conn.commit(); | ||
| break; | ||
| } catch(SQLException e) { | ||
| // Check if the error code indicates a SERIALIZATION_FAILURE. | ||
| if(e.getErrorCode() == 40001) { | ||
| // Signal the database that we will attempt a retry. | ||
| conn.rollback(sp); | ||
| } | ||
| // This is a not a serialization failure, pass it up the chain. | ||
| throw e; | ||
| } | ||
| } | ||
| } | ||
|
|
||
| public static void main(String[] args) throws ClassNotFoundException, SQLException { | ||
| // Load the postgres JDBC driver. | ||
| Class.forName("org.postgresql.Driver"); | ||
|
|
||
| // Connect to the "bank" database. | ||
| Connection db = DriverManager.getConnection("jdbc:postgresql://127.0.0.1:26257/bank?sslmode=disable", "maxroach", ""); | ||
| try { | ||
| // We need to turn off autocommit mode to allow for | ||
| // multi-statement transactions. | ||
| db.setAutoCommit(false); | ||
|
|
||
| RetryableTransaction transfer = transferFunds(1, 2, 100); | ||
| retryTransaction(db, transfer); | ||
| ResultSet res = db.createStatement().executeQuery("SELECT id, balance FROM accounts"); | ||
| while (res.next()) { | ||
| System.out.printf("\taccount %s: %s\n", res.getInt("id"), res.getInt("balance")); | ||
| } | ||
| } catch(InsufficientBalanceException ibe) { | ||
| System.out.println("Insufficient balance"); | ||
| } catch(SQLException sqle) { | ||
| System.out.println("SQLException encountered:" + sqle); | ||
| } catch(Exception e) { | ||
| System.out.println("Unknown exception encountered:" + e); | ||
| } finally { | ||
| // Close the database connection. | ||
| db.close(); | ||
| } | ||
| } | ||
| } |
Empty file.
This file contains bidirectional Unicode text that may be interpreted or compiled differently than what appears below. To review, open the file in an editor that reveals hidden Unicode characters.
Learn more about bidirectional Unicode characters