[CONF] Apache Qpid: LVQ (page edited)

[confluence]

Page Edited : qpid : LVQ LVQ has been edited by Carl Trieloff (Dec 29, 2008). (View changes) Content: Understanding LVQ Last Value Queues are useful youUser Documentation are only interested in the latest value entered into a queue. LVQ semantics are typically used for things like stock symbol updates when all you care about is the latest value for example. Qpid C++ M4 or later supports two types of LVQ semantics: LVQ LVQ_NO_BROWSE LVQ semantics: LVQ uses a header for a key, if the key matches it replaces the message in-place in the queue except a.) if the message with the matching key has been acquired b.) if the message with the matching key has been browsed In these two cases the message is placed into the queue in FIFO, if another message with the same key is received it will the 'un-accessed' message with the same key will be replaced These two exceptions protect the consumer from missing the last update where a consumer or browser accesses a message and an update comes with the same key. [localhost tests]$ ./echotest --mode create_lvq [localhost tests]$ ./echotest --mode write Sending Data: key1=key1.0x7fffdf3f3180 Sending Data: key2=key2.0x7fffdf3f3180 Sending Data: key3=key3.0x7fffdf3f3180 Sending Data: key1=key1.0x7fffdf3f3180 Sending Data: last=last [localhost tests]$ ./echotest --mode browse Receiving Data:key1.0x7fffdf3f3180 Receiving Data:key2.0x7fffdf3f3180 Receiving Data:key3.0x7fffdf3f3180 Receiving Data:last [localhost tests]$ ./echotest --mode write Sending Data: key1=key1.0x7fffe4c7fa10 Sending Data: key2=key2.0x7fffe4c7fa10 Sending Data: key3=key3.0x7fffe4c7fa10 Sending Data: key1=key1.0x7fffe4c7fa10 Sending Data: last=last [localhost tests]$ ./echotest --mode consume Receiving Data:key1.0x7fffdf3f3180 Receiving Data:key2.0x7fffdf3f3180 Receiving Data:key3.0x7fffdf3f3180 Receiving Data:last Receiving Data:key1.0x7fffe4c7fa10 Receiving Data:key2.0x7fffe4c7fa10 Receiving Data:key3.0x7fffe4c7fa10 Receiving Data:last An example h2. LVQ_NO_BROWSE semantics: LVQ uses a header for a key, if the key matches it replaces the message in-place in the queue except a.) if the message with the matching key has been acquired In these two cases the message is placed into the queue in FIFO, if another message with the same key is received it will the 'un-accessed' message with the same key will be replaced Note, in this case browsed messaged are not invalidated, so updates can be missed. An example localhost tests$ ./echotest --mode create_lvq_no_browse localhost tests$ ./echotest --mode write Sending Data: key1=key1.0x7fffce5fb390 Sending Data: key2=key2.0x7fffce5fb390 Sending Data: key3=key3.0x7fffce5fb390 Sending Data: key1=key1.0x7fffce5fb390 Sending Data: last=last localhost tests$ ./echotest --mode write Sending Data: key1=key1.0x7fff346ae440 Sending Data: key2=key2.0x7fff346ae440 Sending Data: key3=key3.0x7fff346ae440 Sending Data: key1=key1.0x7fff346ae440 Sending Data: last=last localhost tests$ ./echotest --mode browse Receiving Data:key1.0x7fff346ae440 Receiving Data:key2.0x7fff346ae440 Receiving Data:key3.0x7fff346ae440 Receiving Data:last localhost tests$ ./echotest --mode browse Receiving Data:key1.0x7fff346ae440 Receiving Data:key2.0x7fff346ae440 Receiving Data:key3.0x7fff346ae440 Receiving Data:last localhost tests$ ./echotest --mode write Sending Data: key1=key1.0x7fff606583e0 Sending Data: key2=key2.0x7fff606583e0 Sending Data: key3=key3.0x7fff606583e0 Sending Data: key1=key1.0x7fff606583e0 Sending Data: last=last localhost tests$ ./echotest --mode consume Receiving Data:key1.0x7fff606583e0 Receiving Data:key2.0x7fff606583e0 Receiving Data:key3.0x7fff606583e0 Receiving Data:last localhost tests$ h2. Example source /* * Licensed to the Apache Software Foundation (ASF) under one or more contributor license agreements. See the NOTICE file distributed with this work for additional information regarding copyright ownership. The ASF licenses this file to you under the Apache License, Version 2.0 (the "License"); you may not use this file except in compliance with the License. You may obtain a copy of the License at http://www.apache.org/licenses/LICENSE-2.0 Unless required by applicable law or agreed to in writing, software distributed under the License is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the License for the specific language governing permissions and limitations under the License. * */ #include <qpid/client/AsyncSession.h> #include <qpid/client/Connection.h> #include <qpid/client/SubscriptionManager.h> #include <qpid/client/Session.h> #include <qpid/client/Message.h> #include <qpid/client/MessageListener.h> #include <qpid/client/QueueOptions.h> #include <iostream> using namespace qpid::client; using namespace qpid::framing; using namespace qpid::sys; using namespace qpid; using namespace std; enum Mode Unknown macro: { CREATE_LVQ, CREATE_LVQ_NO_BROWSE, WRITE, BROWSE, CONSUME} ; const char* modeNames[] = Unknown macro: { "create_lvq","create_lvq_no_browse","write","browse","consume" } ; // istream/ostream ops so Options can read/display Mode. istream& operator>>(istream& in, Mode& mode) Unknown macro: { string s; in >> s; int i = find(modeNames, modeNames+5, s) - modeNames; if (i >= 5) throw Exception("Invalid mode} ostream& operator<<(ostream& out, Mode mode) Unknown macro: { return out << modeNames[mode]; } struct Args : public qpid::Options, public qpid::client::ConnectionSettings { bool help; Mode mode; Args() : qpid::Options("Simple latency test optins"), help(false), mode(BROWSE) Unknown macro: { using namespace qpid; addOptions() ("help", optValue(help), "Print this usage statement") ("broker,b", optValue(host, "HOST"), "Broker host to connect to") ("port,p", optValue(port, "PORT"), "Broker port to connect to") ("username", optValue(username, "USER"), "user name for broker log in.") ("password", optValue(password, "PASSWORD"), "password for broker log in.") ("mechanism", optValue(mechanism, "MECH"), "SASL mechanism to use when authenticating.") ("tcp-nodelay", optValue(tcpNoDelay), "Turn on tcp-nodelay") ("mode", optValue(mode, "'see below'"), "Action mode." "ncreate_lvq} }; class Listener : public MessageListener Unknown macro: { private} ; Listener::Listener(Session& s) : session(s), subscriptions(s), queue("LVQtester") {} void Listener::setup(bool browse) Unknown macro: { // set queue mode args.setOrdering(browse?LVQ_NO_BROWSE} void Listener::browse() Unknown macro: { subscriptions.subscribe(*this, queue, SubscriptionSettings(FlowControl} void Listener::consume() Unknown macro: { subscriptions.subscribe(*this, queue, SubscriptionSettings(FlowControl} void Listener::send(std::string kv) Unknown macro: { request.getDeliveryProperties().setRoutingKey(queue); std} void Listener::received(Message& response) { cout << "Receiving Data:" << response.getData() << std::endl; /* if (response.getData() == "last") Unknown macro: { subscriptions.cancel(queue); } */ } int main(int argc, char** argv) { Args opts; opts.parse(argc, argv); if (opts.help) Unknown macro: { std} Connection connection; try { connection.open(opts); Session session = connection.newSession(); Listener listener(session); switch (opts.mode) Unknown macro: { case CONSUME} connection.close(); return 0; } catch(const std::exception& error) Unknown macro: { std} return 1; }

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