spanner-jdbc: Step 23 - DmlBatch

[olavloite]

Adds DmlBatch. DML batches are similar to DDL batches, except they execute DML instead of DDL statements. DML batches are executed like this:

START BATCH DML;
UPDATE FOO SET BAR=1WHERE ID=2;
RUN BATCH;

An active batch can be aborted by executing the ABORT BATCH statement.

DML batches can be executed while the transaction is in autocommit mode, which means that the effects of the batch will be visible to all other users directly after the RUN BATCH statement has finished executing. DML batches can also be executed as part of a read/write transaction. As a connection only allows one UnitOfWork to be active at any time, and both a read/write transaction and a DML batch is a UnitOfWork, the DML batch is executed as an nested batch of the active transaction. When RUN BATCH is executed, the batch of DML statements are executed on the active read/write transaction, and its effects will only be visible to other users once the transaction has been committed.