This package contains FastAndRuthlessDiffImpl, which is used to reduce network bandwidth when working with byte[] objects that are being changed slightly by a client before being sent back to a server.

Alternative binary diff packages go for maximum compression at the expense of CPU time. FastAndRuthlessDiffImpl seeks a compromise between compression and speed.

Sample usage - client side:

final String key = "foo"; final int oldHashcode = FastAndRuthlessDiffImpl.deterministicHashcode(oldArray); final int maxNumberOfChanges = 12;

byte[] delta = i.calculateDiff(oldArray, newArray, maxNumberOfChanges); ClientResponse r = client.callProcedure("DiffedUpdate", key, delta, oldHashcode);

Sample usage - server side:

import org.voltdb.SQLStmt;

import org.voltdb.VoltProcedure; import org.voltdb.VoltTable;

import com.voltdb.voltutil.server.; import com.voltdb.voltutil.binarydiff.; import com.voltdb.voltutil.binarydiff.exceptions.HashCodeMismatchException;

public class DiffedUpdate extends VoltProcedure {

   private static final long HASHCODE_MISMATCH = -2;
   private static final long NO_SUCH_KEY = -1;
   private static final long UPDATE_OK = 0;

   public final SQLStmt queryStmt = new SQLStmt("SELECT value FROM store WHERE key = ?;");
   public final SQLStmt updateStmt = new SQLStmt("UPDATE store SET value = ? WHERE key = ?;");

   FastAndRuthlessDiffImpl theDiffImpl = new FastAndRuthlessDiffImpl();

   public VoltTable[] run(String key, byte[] deltaValue, int hashcode) {

           // Define a single row output table
           VoltTable statusTable = ProcedureHelper.GetStatusTable();
           VoltTable[] results = { statusTable };

           voltQueueSQL(queryStmt, key);

           final VoltTable[] queryResults = voltExecuteSQL();

           queryResults[0].resetRowPosition();
           if (queryResults[0].advanceRow()) {

                   final byte[] oldPayload = queryResults[0].getVarbinary("VALUE");
                   byte[] newPayload = null;

                   try {
                           newPayload = theDiffImpl.applyDiff(oldPayload, deltaValue, hashcode);
                           voltQueueSQL(updateStmt, newPayload, key);
                           voltExecuteSQL(true);
                           ProcedureHelper.setStatus(statusTable, UPDATE_OK, null);

                   } catch (HashCodeMismatchException e) {
                           ProcedureHelper.setStatus(statusTable, HASHCODE_MISMATCH,
                                           "Got " + hashcode + ", needed " + oldPayload.hashCode());
                   }

           } else {

                   // There is no current row to diff.
                   ProcedureHelper.setStatus(statusTable, NO_SUCH_KEY, "No such Key");
           }

           return results;

   }

}

}

Author: [email protected]