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: drolfe@voltdb.com