Re: Connection.setsavepoint() / releaseSavepoint() is not thread-safe

I have refined the test as follows:

package cpssd.db;

import org.junit.Test;

import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.SQLException;
import java.sql.Savepoint;
import java.util.concurrent.CountDownLatch;

/**
* See issue #251 at
* https://www.assembla.com/spaces/cirruspoint/tickets/251
* and the corresponding PostgreSQL issue #10847.
*
* @author Christian Schlichtherle
*/
public class Ticket251IT {

private static final String CONNECTION_STRING = "jdbc:postgresql:postgres";
private static final int NUM_THREADS = 8;

@Test public void foo() throws SQLException, InterruptedException {
try (Connection c = DriverManager.getConnection(CONNECTION_STRING)) {
c.setAutoCommit(false);
final Runnable task = new Runnable() {
final CountDownLatch startSignal = new CountDownLatch(NUM_THREADS);

@Override public void run() {
try {
// TODO: Once the bug in PostgreSQL has been fixed, the
// synchronized (c) statement can get removed.
Savepoint sp;
synchronized (c) {
sp = c.setSavepoint();
}
try {
// Insert transaction script here...
startSignal.countDown();
startSignal.await();
} finally {
synchronized (c) {
c.releaseSavepoint(sp);
}
}
} catch (SQLException | InterruptedException e) {
e.printStackTrace();
}
}
};
final Thread[] threads = new Thread[NUM_THREADS];
for (int i = 0; i < threads.length; i++)
(threads[i] = new Thread(task)).start();
for (Thread thread : threads)
thread.join();
}
}
}

As you can see, I am now synchronizing all access on the connection. However, when running this test, every now and then it produces output like the following:

org.postgresql.util.PSQLException: ERROR: current transaction is aborted, commands ignored until end of transaction block
at org.postgresql.core.v3.QueryExecutorImpl.receiveErrorResponse(QueryExecutorImpl.java:2161)
at org.postgresql.core.v3.QueryExecutorImpl.processResults(QueryExecutorImpl.java:1890)
at org.postgresql.core.v3.QueryExecutorImpl.execute(QueryExecutorImpl.java:255)
at org.postgresql.jdbc2.AbstractJdbc2Statement.execute(AbstractJdbc2Statement.java:559)
at org.postgresql.jdbc2.AbstractJdbc2Statement.executeWithFlags(AbstractJdbc2Statement.java:403)
at org.postgresql.jdbc2.AbstractJdbc2Connection.execSQLUpdate(AbstractJdbc2Connection.java:376)
at org.postgresql.jdbc3.AbstractJdbc3Connection.releaseSavepoint(AbstractJdbc3Connection.java:192)
at cpssd.db.Ticket251IT$1.run(Ticket251IT.java:43)
at java.lang.Thread.run(Thread.java:745)
org.postgresql.util.PSQLException: ERROR: current transaction is aborted, commands ignored until end of transaction block
at org.postgresql.core.v3.QueryExecutorImpl.receiveErrorResponse(QueryExecutorImpl.java:2161)
at org.postgresql.core.v3.QueryExecutorImpl.processResults(QueryExecutorImpl.java:1890)
at org.postgresql.core.v3.QueryExecutorImpl.execute(QueryExecutorImpl.java:255)
at org.postgresql.jdbc2.AbstractJdbc2Statement.execute(AbstractJdbc2Statement.java:559)
at org.postgresql.jdbc2.AbstractJdbc2Statement.executeWithFlags(AbstractJdbc2Statement.java:403)
at org.postgresql.jdbc2.AbstractJdbc2Connection.execSQLUpdate(AbstractJdbc2Connection.java:376)
at org.postgresql.jdbc3.AbstractJdbc3Connection.releaseSavepoint(AbstractJdbc3Connection.java:192)
at cpssd.db.Ticket251IT$1.run(Ticket251IT.java:43)
at java.lang.Thread.run(Thread.java:745)
org.postgresql.util.PSQLException: ERROR: current transaction is aborted, commands ignored until end of transaction block
at org.postgresql.core.v3.QueryExecutorImpl.receiveErrorResponse(QueryExecutorImpl.java:2161)
at org.postgresql.core.v3.QueryExecutorImpl.processResults(QueryExecutorImpl.java:1890)
at org.postgresql.core.v3.QueryExecutorImpl.execute(QueryExecutorImpl.java:255)
at org.postgresql.jdbc2.AbstractJdbc2Statement.execute(AbstractJdbc2Statement.java:559)
at org.postgresql.jdbc2.AbstractJdbc2Statement.executeWithFlags(AbstractJdbc2Statement.java:403)
at org.postgresql.jdbc2.AbstractJdbc2Connection.execSQLUpdate(AbstractJdbc2Connection.java:376)
at org.postgresql.jdbc3.AbstractJdbc3Connection.releaseSavepoint(AbstractJdbc3Connection.java:192)
at cpssd.db.Ticket251IT$1.run(Ticket251IT.java:43)
at java.lang.Thread.run(Thread.java:745)
org.postgresql.util.PSQLException: ERROR: no such savepoint
at org.postgresql.core.v3.QueryExecutorImpl.receiveErrorResponse(QueryExecutorImpl.java:2161)
at org.postgresql.core.v3.QueryExecutorImpl.processResults(QueryExecutorImpl.java:1890)
at org.postgresql.core.v3.QueryExecutorImpl.execute(QueryExecutorImpl.java:255)
at org.postgresql.jdbc2.AbstractJdbc2Statement.execute(AbstractJdbc2Statement.java:559)
at org.postgresql.jdbc2.AbstractJdbc2Statement.executeWithFlags(AbstractJdbc2Statement.java:403)
at org.postgresql.jdbc2.AbstractJdbc2Connection.execSQLUpdate(AbstractJdbc2Connection.java:376)
at org.postgresql.jdbc3.AbstractJdbc3Connection.releaseSavepoint(AbstractJdbc3Connection.java:192)
at cpssd.db.Ticket251IT$1.run(Ticket251IT.java:43)
at java.lang.Thread.run(Thread.java:745)

Regards,
Christian Schlichtherle

Am 04.07.2014 um 10:10 schrieb Christian Schlichtherle <christian(at)schlichtherle(dot)de>:

> Hi everyone,
>
> I have already posted this bug as #10847 to pqsql-bugs(at)postgresql(dot)org, but was redirected here:
>
> The following test code…
> import org.junit.Test;
>
> import java.sql.Connection;
> import java.sql.DriverManager;
> import java.sql.SQLException;
> import java.sql.Savepoint;
> import java.util.concurrent.CountDownLatch;
>
> /** @author Christian Schlichtherle */
> public class Ticket251IT {
>
> private static final String CONNECTION_STRING = "jdbc:postgresql:postgres";
> private static final int NUM_THREADS = 2;
>
> @Test public void foo() throws SQLException, InterruptedException {
> try (Connection c = DriverManager.getConnection(CONNECTION_STRING)) {
> c.setAutoCommit(false);
> final Runnable task = new Runnable() {
> final CountDownLatch startSignal = new CountDownLatch(NUM_THREADS);
>
> @Override public void run() {
> try {
> startSignal.countDown();
> startSignal.await();
> // FIXME: This idiom doesn't work on a shared connection!
> Savepoint sp = c.setSavepoint();
> try {
> // Insert transaction script here...
> } finally {
> c.releaseSavepoint(sp);
> }
> } catch (SQLException | InterruptedException e) {
> e.printStackTrace();
> }
> }
> };
> final Thread[] threads = new Thread[NUM_THREADS];
> for (int i = 0; i < threads.length; i++)
> (threads[i] = new Thread(task)).start();
> for (Thread thread : threads)
> thread.join();
> },
> }
> }
> …frequently produces the following output…
> org.postgresql.util.PSQLException: ERROR: no such savepoint
> at org.postgresql.core.v3.QueryExecutorImpl.receiveErrorResponse(QueryExecutorImpl.java:2161)
> at org.postgresql.core.v3.QueryExecutorImpl.processResults(QueryExecutorImpl.java:1890)
> at org.postgresql.core.v3.QueryExecutorImpl.execute(QueryExecutorImpl.java:255)
> at org.postgresql.jdbc2.AbstractJdbc2Statement.execute(AbstractJdbc2Statement.java:559)
> at org.postgresql.jdbc2.AbstractJdbc2Statement.executeWithFlags(AbstractJdbc2Statement.java:403)
> at org.postgresql.jdbc2.AbstractJdbc2Connection.execSQLUpdate(AbstractJdbc2Connection.java:376)
> at org.postgresql.jdbc3.AbstractJdbc3Connection.releaseSavepoint(AbstractJdbc3Connection.java:192)
> at cpssd.db.Ticket251IT$1.run(Ticket251IT.java:32)
> at java.lang.Thread.run(Thread.java:745)
> The obvious workaround is to put all calls on the connection into a synchronized (whatever) { … } block. However, although the workaround works fine when applied to this isolated test case, it fails in my production code. I have yet to find out why that is. Nevertheless, this seems to be a bug in the JDBC driver.
>
> The real use case behind this simplified test case is to distribute work to multiple threads. A parent thread creates the connection and starts a transaction, then spawns a number of child threads. Each child thread creates a save point, does its work and releases or rolls back the save point again. If all child threads succeed, the parent thread then commits the entire transaction. I figure from this document that this is indeed „fair use“ of a Connection. Thus, it would be superb if PostgreSQL could support it.
>
> Regards,
> Christian Schlichtherle