Cassandra Datastax BatchStatement with Lightweight Transactions - cassandra

Question

I'm having difficulty combining BatchStatement and Lightweight Transactions using the Datastax java driver.
Consider the following:
String batch =
"BEGIN BATCH "
+ "Update mykeyspace.mytable set record_version = 102 where id = '" + id + "' if record_version = 101;
" <additional batched statements>
+ "APPLY BATCH";
Row row = session.execute(batch).one();
if (! row.getBool("[applied]")) {
throw new RuntimeException("Optimistic Lock Failure!");
}
This functions as expected and indicates whether my lightweight transaction succeeded and my batch was applied. All is good. However if I try the same thing using a BatchStatement, I run into a couple of problems:
-- My lightweight transaction "if" clause is ignored and the update is always applied
-- The "Row" result is null making it impossible to execute the final row.getBool("[applied]") check.
String update = "Update mykeyspace.mytable set record_version = ? where id = ? if record_version = ?";
PreparedStatement pStmt = getSession().prepare(update);
BatchStatement batch = new BatchStatement();
batch.add(new BoundStatement(pStmt).bind(newVersion, id, oldVersion));
Row row = session.execute(batch).one(); <------ Row is null!
if (! row.getBool("[applied]")) {
throw new RuntimeException("Optimistic Lock Failure!");
}
Am I doing this wrong? Or is this a limitation with the datastax BatchStatement?

Answer 1

I am encountering this same issue. I opened a ticket with DataStax support yesterday and received the following answer:
Currently Lightweight Transactions as PreparedStatements within a BATCH are not supported. This is why you are encountering this issue.
There is nothing on the immediate roadmap to include this feature in Cassandra.
That suggests eliminating the PreparedStatement will workaround the issue. I'm going to try that myself, but haven't yet.
[Update]
I've been trying to work around this issue. Based on the earlier feedback, I assumed the restriction was on using a PreparedStatement for the conditional update.
I tried changing my code to not use a PreparedStatement, but that still didn't work when using a BatchStatement that contained a RegularStatement instead of a PreparedStatement.
BatchStatement batchStatement = new BatchStatement();
batchStatement.add(conditionalRegularStatement);
session.executeQuery(batchStatement);
They only thing that seems to work is to do an executeQuery with a raw query string that includes the batch.
session.executeQuery("BEGIN BATCH " + conditionalRegularStatement.getQueryString() + " APPLY BATCH");

Answer 2

Update:
This issue is resolved in CASSANDRA-7337 which was fixed in C* 2.0.9.
The latest DataStax Enterprise is now on 2.0.11. If you are seeing this issue ==> Upgrade!

Answer 3

The 2nd code snippet doesn't look right to me (there's no constructor taking a string or you've missed the prepared statement).
Can you try instead the following:
String update = "Update mykeyspace.mytable set record_version = ? where id = ? if record_version = ?";
PreparedStatement pStmt = session.prepare(update);
BatchStatement batch = new BatchStatement();
batch.add(pStmt.bind(newVersion, id, recordVersion));
Row row = session.execute(batch).one();
if (! row.getBool("[applied]")) {
throw new RuntimeException("Optimistic Lock Failure!");
}