RecordingTransaction recipe

A RecordingTransaction is an implementation of Transaction that logs all transaction operations (i.e GET, SET, or DELETE) to a TxLog object for later uses such as exporting data. The code below shows how a RecordingTransaction is created by wrapping a Transaction object:

RecordingTransactionBase rtx = RecordingTransactionBase.wrap(tx);

A predicate function can be passed to wrap method to select which log entries to record. The code below only records log entries whose column family is meta:

RecordingTransactionBase rtx = RecordingTransactionBase.wrap(tx,
                               le -> le.getColumn().getFamily().toString().equals("meta"));

After creating a RecordingTransaction, users can use it as they would use a Transaction object.

Bytes value = rtx.get(Bytes.of("r1"), new Column("cf1", "cq1"));

While SET or DELETE operations are always recorded to the log, GET operations are only recorded if a value was found at the requested row/column. Also, if a GET method returns an iterator, only the GET operations that are retrieved from the iterator are logged. GET operations are logged as they are necessary if you want to determine the changes made by the transaction.

When you are done operating on the transaction, you can retrieve the TxLog using the following code:

TxLog myTxLog = rtx.getTxLog()

Below is example code of how a RecordingTransaction can be used in an observer to record all operations performed by the transaction in a TxLog. In this example, a GET (if data exists) and SET operation will be logged. This TxLog can be added to an export queue and later used to export updates from Fluo.

public class MyObserver extends AbstractObserver {

    private static final TYPEL = new TypeLayer(new StringEncoder());
    private ExportQueue<Bytes, TxLog> exportQueue;

    public void process(TransactionBase tx, Bytes row, Column col) {

        // create recording transaction (rtx)
        RecordingTransactionBase rtx = RecordingTransactionBase.wrap(tx);
        // use rtx to create a typed transaction & perform operations
        TypedTransactionBase ttx = TYPEL.wrap(rtx);
        int count = ttx.get().row(row).fam("meta").qual("counter1").toInteger(0);
        // when finished performing operations, retrieve transaction log
        TxLog txLog = rtx.getTxLog()

        // add txLog to exportQueue if not empty
        if (!txLog.isEmpty()) {
          //do not pass rtx to exportQueue.add()
          exportQueue.add(tx, row, txLog)