+++ /dev/null
-// -*- mode:C++; tab-width:8; c-basic-offset:2; indent-tabs-mode:t -*-
-// vim: ts=8 sw=2 smarttab
-/*
- * Ceph - scalable distributed file system
- *
- * Copyright (C) 2004-2006 Sage Weil <sage@newdream.net>
- *
- * This is free software; you can redistribute it and/or
- * modify it under the terms of the GNU Lesser General Public
- * License version 2.1, as published by the Free Software
- * Foundation. See file COPYING.
- *
- */
-
-/*
-time---->
-
-cccccccccccccccccca????????????????????????????????????????
-cccccccccccccccccca????????????????????????????????????????
-cccccccccccccccccca???????????????????????????????????????? leader
-cccccccccccccccccc?????????????????????????????????????????
-ccccc??????????????????????????????????????????????????????
-
-last_committed
-
-pn_from
-pn
-
-a 12v
-b 12v
-c 14v
-d
-e 12v
-*/
-
-/**
- * Paxos storage layout and behavior
- *
- * Currently, we use a key/value store to hold all the Paxos-related data, but
- * it can logically be depicted as this:
- *
- * paxos:
- * first_committed -> 1
- * last_committed -> 4
- * 1 -> value_1
- * 2 -> value_2
- * 3 -> value_3
- * 4 -> value_4
- *
- * Since we are relying on a k/v store supporting atomic transactions, we can
- * guarantee that if 'last_committed' has a value of '4', then we have up to
- * version 4 on the store, and no more than that; the same applies to
- * 'first_committed', which holding '1' will strictly meaning that our lowest
- * version is 1.
- *
- * Each version's value (value_1, value_2, ..., value_n) is a blob of data,
- * incomprehensible to the Paxos. These values are proposed to the Paxos on
- * propose_new_value() and each one is a transaction encoded in a bufferlist.
- *
- * The Paxos will write the value to disk, associating it with its version,
- * but will take a step further: the value shall be decoded, and the operations
- * on that transaction shall be applied during the same transaction that will
- * write the value's encoded bufferlist to disk. This behavior ensures that
- * whatever is being proposed will only be available on the store when it is
- * applied by Paxos, which will then be aware of such new values, guaranteeing
- * the store state is always consistent without requiring shady workarounds.
- *
- * So, let's say that FooMonitor proposes the following transaction, neatly
- * encoded on a bufferlist of course:
- *
- * Tx_Foo
- * put(foo, last_committed, 3)
- * put(foo, 3, foo_value_3)
- * erase(foo, 2)
- * erase(foo, 1)
- * put(foo, first_committed, 3)
- *
- * And knowing that the Paxos is proposed Tx_Foo as a bufferlist, once it is
- * ready to commit, and assuming we are now committing version 5 of the Paxos,
- * we will do something along the lines of:
- *
- * Tx proposed_tx;
- * proposed_tx.decode(Tx_foo_bufferlist);
- *
- * Tx our_tx;
- * our_tx.put(paxos, last_committed, 5);
- * our_tx.put(paxos, 5, Tx_foo_bufferlist);
- * our_tx.append(proposed_tx);
- *
- * store_apply(our_tx);
- *
- * And the store should look like this after we apply 'our_tx':
- *
- * paxos:
- * first_committed -> 1
- * last_committed -> 5
- * 1 -> value_1
- * 2 -> value_2
- * 3 -> value_3
- * 4 -> value_4
- * 5 -> Tx_foo_bufferlist
- * foo:
- * first_committed -> 3
- * last_committed -> 3
- * 3 -> foo_value_3
- *
- */
-
-#ifndef CEPH_MON_PAXOS_H
-#define CEPH_MON_PAXOS_H
-
-#include "include/types.h"
-#include "mon_types.h"
-#include "include/buffer.h"
-#include "msg/msg_types.h"
-#include "include/Context.h"
-#include "common/perf_counters.h"
-#include <errno.h>
-
-#include "MonitorDBStore.h"
-#include "mon/MonOpRequest.h"
-
-class Monitor;
-class MMonPaxos;
-
-enum {
- l_paxos_first = 45800,
- l_paxos_start_leader,
- l_paxos_start_peon,
- l_paxos_restart,
- l_paxos_refresh,
- l_paxos_refresh_latency,
- l_paxos_begin,
- l_paxos_begin_keys,
- l_paxos_begin_bytes,
- l_paxos_begin_latency,
- l_paxos_commit,
- l_paxos_commit_keys,
- l_paxos_commit_bytes,
- l_paxos_commit_latency,
- l_paxos_collect,
- l_paxos_collect_keys,
- l_paxos_collect_bytes,
- l_paxos_collect_latency,
- l_paxos_collect_uncommitted,
- l_paxos_collect_timeout,
- l_paxos_accept_timeout,
- l_paxos_lease_ack_timeout,
- l_paxos_lease_timeout,
- l_paxos_store_state,
- l_paxos_store_state_keys,
- l_paxos_store_state_bytes,
- l_paxos_store_state_latency,
- l_paxos_share_state,
- l_paxos_share_state_keys,
- l_paxos_share_state_bytes,
- l_paxos_new_pn,
- l_paxos_new_pn_latency,
- l_paxos_last,
-};
-
-
-// i am one state machine.
-/**
- * This libary is based on the Paxos algorithm, but varies in a few key ways:
- * 1- Only a single new value is generated at a time, simplifying the recovery logic.
- * 2- Nodes track "committed" values, and share them generously (and trustingly)
- * 3- A 'leasing' mechanism is built-in, allowing nodes to determine when it is
- * safe to "read" their copy of the last committed value.
- *
- * This provides a simple replication substrate that services can be built on top of.
- * See PaxosService.h
- */
-class Paxos {
- /**
- * @defgroup Paxos_h_class Paxos
- * @{
- */
- /**
- * The Monitor to which this Paxos class is associated with.
- */
- Monitor *mon;
-
- /// perf counter for internal instrumentations
- PerfCounters *logger;
-
- void init_logger();
-
- // my state machine info
- const string paxos_name;
-
- friend class Monitor;
- friend class PaxosService;
-
- list<std::string> extra_state_dirs;
-
- // LEADER+PEON
-
- // -- generic state --
-public:
- /**
- * @defgroup Paxos_h_states States on which the leader/peon may be.
- * @{
- */
- enum {
- /**
- * Leader/Peon is in Paxos' Recovery state
- */
- STATE_RECOVERING,
- /**
- * Leader/Peon is idle, and the Peon may or may not have a valid lease.
- */
- STATE_ACTIVE,
- /**
- * Leader/Peon is updating to a new value.
- */
- STATE_UPDATING,
- /*
- * Leader proposing an old value
- */
- STATE_UPDATING_PREVIOUS,
- /*
- * Leader/Peon is writing a new commit. readable, but not
- * writeable.
- */
- STATE_WRITING,
- /*
- * Leader/Peon is writing a new commit from a previous round.
- */
- STATE_WRITING_PREVIOUS,
- // leader: refresh following a commit
- STATE_REFRESH,
- // Shutdown after WRITING or WRITING_PREVIOUS
- STATE_SHUTDOWN
- };
-
- /**
- * Obtain state name from constant value.
- *
- * @note This function will raise a fatal error if @p s is not
- * a valid state value.
- *
- * @param s State value.
- * @return The state's name.
- */
- static const string get_statename(int s) {
- switch (s) {
- case STATE_RECOVERING:
- return "recovering";
- case STATE_ACTIVE:
- return "active";
- case STATE_UPDATING:
- return "updating";
- case STATE_UPDATING_PREVIOUS:
- return "updating-previous";
- case STATE_WRITING:
- return "writing";
- case STATE_WRITING_PREVIOUS:
- return "writing-previous";
- case STATE_REFRESH:
- return "refresh";
- case STATE_SHUTDOWN:
- return "shutdown";
- default:
- return "UNKNOWN";
- }
- }
-
-private:
- /**
- * The state we are in.
- */
- int state;
- /**
- * @}
- */
- int commits_started = 0;
-
- Cond shutdown_cond;
-
-public:
- /**
- * Check if we are recovering.
- *
- * @return 'true' if we are on the Recovering state; 'false' otherwise.
- */
- bool is_recovering() const { return (state == STATE_RECOVERING); }
- /**
- * Check if we are active.
- *
- * @return 'true' if we are on the Active state; 'false' otherwise.
- */
- bool is_active() const { return state == STATE_ACTIVE; }
- /**
- * Check if we are updating.
- *
- * @return 'true' if we are on the Updating state; 'false' otherwise.
- */
- bool is_updating() const { return state == STATE_UPDATING; }
-
- /**
- * Check if we are updating/proposing a previous value from a
- * previous quorum
- */
- bool is_updating_previous() const { return state == STATE_UPDATING_PREVIOUS; }
-
- /// @return 'true' if we are writing an update to disk
- bool is_writing() const { return state == STATE_WRITING; }
-
- /// @return 'true' if we are writing an update-previous to disk
- bool is_writing_previous() const { return state == STATE_WRITING_PREVIOUS; }
-
- /// @return 'true' if we are refreshing an update just committed
- bool is_refresh() const { return state == STATE_REFRESH; }
-
- /// @return 'true' if we are in the process of shutting down
- bool is_shutdown() const { return state == STATE_SHUTDOWN; }
-
-private:
- /**
- * @defgroup Paxos_h_recovery_vars Common recovery-related member variables
- * @note These variables are common to both the Leader and the Peons.
- * @{
- */
- /**
- *
- */
- version_t first_committed;
- /**
- * Last Proposal Number
- *
- * @todo Expand description
- */
- version_t last_pn;
- /**
- * Last committed value's version.
- *
- * On both the Leader and the Peons, this is the last value's version that
- * was accepted by a given quorum and thus committed, that this instance
- * knows about.
- *
- * @note It may not be the last committed value's version throughout the
- * system. If we are a Peon, we may have not been part of the quorum
- * that accepted the value, and for this very same reason we may still
- * be a (couple of) version(s) behind, until we learn about the most
- * recent version. This should only happen if we are not active (i.e.,
- * part of the quorum), which should not happen if we are up, running
- * and able to communicate with others -- thus able to be part of the
- * monmap and trigger new elections.
- */
- version_t last_committed;
- /**
- * Last committed value's time.
- *
- * When the commit finished.
- */
- utime_t last_commit_time;
- /**
- * The last Proposal Number we have accepted.
- *
- * On the Leader, it will be the Proposal Number picked by the Leader
- * itself. On the Peon, however, it will be the proposal sent by the Leader
- * and it will only be updated if its value is higher than the one
- * already known by the Peon.
- */
- version_t accepted_pn;
- /**
- * The last_committed epoch of the leader at the time we accepted the last pn.
- *
- * This has NO SEMANTIC MEANING, and is there only for the debug output.
- */
- version_t accepted_pn_from;
- /**
- * Map holding the first committed version by each quorum member.
- *
- * The versions kept in this map are updated during the collect phase.
- * When the Leader starts the collect phase, each Peon will reply with its
- * first committed version, which will then be kept in this map.
- */
- map<int,version_t> peer_first_committed;
- /**
- * Map holding the last committed version by each quorum member.
- *
- * The versions kept in this map are updated during the collect phase.
- * When the Leader starts the collect phase, each Peon will reply with its
- * last committed version, which will then be kept in this map.
- */
- map<int,version_t> peer_last_committed;
- /**
- * @}
- */
-
- // active (phase 2)
- /**
- * @defgroup Paxos_h_active_vars Common active-related member variables
- * @{
- */
- /**
- * When does our read lease expires.
- *
- * Instead of performing a full commit each time a read is requested, we
- * keep leases. Each lease will have an expiration date, which may or may
- * not be extended.
- */
- utime_t lease_expire;
- /**
- * List of callbacks waiting for our state to change into STATE_ACTIVE.
- */
- list<Context*> waiting_for_active;
- /**
- * List of callbacks waiting for the chance to read a version from us.
- *
- * Each entry on the list may result from an attempt to read a version that
- * wasn't available at the time, or an attempt made during a period during
- * which we could not satisfy the read request. The first case happens if
- * the requested version is greater than our last committed version. The
- * second scenario may happen if we are recovering, or if we don't have a
- * valid lease.
- *
- * The list will be woken up once we change to STATE_ACTIVE with an extended
- * lease -- which can be achieved if we have everyone on the quorum on board
- * with the latest proposal, or if we don't really care about the remaining
- * uncommitted values --, or if we're on a quorum of one.
- */
- list<Context*> waiting_for_readable;
- /**
- * @}
- */
-
- // -- leader --
- // recovery (paxos phase 1)
- /**
- * @defgroup Paxos_h_leader_recovery Leader-specific Recovery-related vars
- * @{
- */
- /**
- * Number of replies to the collect phase we've received so far.
- *
- * This variable is reset to 1 each time we start a collect phase; it is
- * incremented each time we receive a reply to the collect message, and
- * is used to determine whether or not we have received replies from the
- * whole quorum.
- */
- unsigned num_last;
- /**
- * Uncommitted value's version.
- *
- * If we have, or end up knowing about, an uncommitted value, then its
- * version will be kept in this variable.
- *
- * @note If this version equals @p last_committed+1 when we reach the final
- * steps of recovery, then the algorithm will assume this is a value
- * the Leader does not know about, and trustingly the Leader will
- * propose this version's value.
- */
- version_t uncommitted_v;
- /**
- * Uncommitted value's Proposal Number.
- *
- * We use this variable to assess if the Leader should take into consideration
- * an uncommitted value sent by a Peon. Given that the Peon will send back to
- * the Leader the last Proposal Number it accepted, the Leader will be able
- * to infer if this value is more recent than the one the Leader has, thus
- * more relevant.
- */
- version_t uncommitted_pn;
- /**
- * Uncommitted Value.
- *
- * If the system fails in-between the accept replies from the Peons and the
- * instruction to commit from the Leader, then we may end up with accepted
- * but yet-uncommitted values. During the Leader's recovery, it will attempt
- * to bring the whole system to the latest state, and that means committing
- * past accepted but uncommitted values.
- *
- * This variable will hold an uncommitted value, which may originate either
- * on the Leader, or learnt by the Leader from a Peon during the collect
- * phase.
- */
- bufferlist uncommitted_value;
- /**
- * Used to specify when an on-going collect phase times out.
- */
- Context *collect_timeout_event;
- /**
- * @}
- */
-
- // active
- /**
- * @defgroup Paxos_h_leader_active Leader-specific Active-related vars
- * @{
- */
- /**
- * Set of participants (Leader & Peons) that have acked a lease extension.
- *
- * Each Peon that acknowledges a lease extension will have its place in this
- * set, which will be used to account for all the acks from all the quorum
- * members, guaranteeing that we trigger new elections if some don't ack in
- * the expected timeframe.
- */
- set<int> acked_lease;
- /**
- * Callback responsible for extending the lease periodically.
- */
- Context *lease_renew_event;
- /**
- * Callback to trigger new elections once the time for acks is out.
- */
- Context *lease_ack_timeout_event;
- /**
- * @}
- */
- /**
- * @defgroup Paxos_h_peon_active Peon-specific Active-related vars
- * @{
- */
- /**
- * Callback to trigger new elections when the Peon's lease times out.
- *
- * If the Peon's lease is extended, this callback will be reset (i.e.,
- * we cancel the event and reschedule a new one with starting from the
- * beginning).
- */
- Context *lease_timeout_event;
- /**
- * @}
- */
-
- // updating (paxos phase 2)
- /**
- * @defgroup Paxos_h_leader_updating Leader-specific Updating-related vars
- * @{
- */
- /**
- * New Value being proposed to the Peons.
- *
- * This bufferlist holds the value the Leader is proposing to the Peons, and
- * that will be committed if the Peons do accept the proposal.
- */
- bufferlist new_value;
- /**
- * Set of participants (Leader & Peons) that accepted the new proposed value.
- *
- * This set is used to keep track of those who have accepted the proposed
- * value, so the leader may know when to issue a commit (when a majority of
- * participants has accepted the proposal), and when to extend the lease
- * (when all the quorum members have accepted the proposal).
- */
- set<int> accepted;
- /**
- * Callback to trigger a new election if the proposal is not accepted by the
- * full quorum within a given timeframe.
- *
- * If the full quorum does not accept the proposal, then it means that the
- * Leader may no longer be recognized as the leader, or that the quorum has
- * changed, and the value may have not reached all the participants. Thus,
- * the leader must call new elections, and go through a recovery phase in
- * order to propagate the new value throughout the system.
- *
- * This does not mean that we won't commit. We will commit as soon as we
- * have a majority of acceptances. But if we do not have full acceptance
- * from the quorum, then we cannot extend the lease, as some participants
- * may not have the latest committed value.
- */
- Context *accept_timeout_event;
-
- /**
- * List of callbacks waiting for it to be possible to write again.
- *
- * @remarks It is not possible to write if we are not the Leader, or we are
- * not on the active state, or if the lease has expired.
- */
- list<Context*> waiting_for_writeable;
- /**
- * List of callbacks waiting for a commit to finish.
- *
- * @remarks This may be used to a) wait for an on-going commit to finish
- * before we proceed with, say, a new proposal; or b) wait for the
- * next commit to be finished so we are sure that our value was
- * fully committed.
- */
- list<Context*> waiting_for_commit;
-
- /**
- * Pending proposal transaction
- *
- * This is the transaction that is under construction and pending
- * proposal. We will add operations to it until we decide it is
- * time to start a paxos round.
- */
- MonitorDBStore::TransactionRef pending_proposal;
-
- /**
- * Finishers for pending transaction
- *
- * These are waiting for updates in the pending proposal/transaction
- * to be committed.
- */
- list<Context*> pending_finishers;
-
- /**
- * Finishers for committing transaction
- *
- * When the pending_proposal is submitted, pending_finishers move to
- * this list. When it commits, these finishers are notified.
- */
- list<Context*> committing_finishers;
-
- /**
- * @defgroup Paxos_h_sync_warns Synchronization warnings
- * @todo Describe these variables
- * @{
- */
- utime_t last_clock_drift_warn;
- int clock_drift_warned;
- /**
- * @}
- */
-
- /**
- * Should be true if we have proposed to trim, or are in the middle of
- * trimming; false otherwise.
- */
- bool trimming;
-
- /**
- * true if we want trigger_propose to *not* propose (yet)
- */
- bool plugged = false;
-
- /**
- * @defgroup Paxos_h_callbacks Callback classes.
- * @{
- */
- /**
- * Callback class responsible for handling a Collect Timeout.
- */
- class C_CollectTimeout;
- /**
- * Callback class responsible for handling an Accept Timeout.
- */
- class C_AcceptTimeout;
- /**
- * Callback class responsible for handling a Lease Ack Timeout.
- */
- class C_LeaseAckTimeout;
-
- /**
- * Callback class responsible for handling a Lease Timeout.
- */
- class C_LeaseTimeout;
-
- /**
- * Callback class responsible for handling a Lease Renew Timeout.
- */
- class C_LeaseRenew;
-
- class C_Trimmed;
- /**
- *
- */
-public:
- class C_Proposal : public Context {
- Context *proposer_context;
- public:
- bufferlist bl;
- // for debug purposes. Will go away. Soon.
- bool proposed;
- utime_t proposal_time;
-
- C_Proposal(Context *c, bufferlist& proposal_bl) :
- proposer_context(c),
- bl(proposal_bl),
- proposed(false),
- proposal_time(ceph_clock_now())
- { }
-
- void finish(int r) override {
- if (proposer_context) {
- proposer_context->complete(r);
- proposer_context = NULL;
- }
- }
- };
- /**
- * @}
- */
-private:
- /**
- * @defgroup Paxos_h_election_triggered Steps triggered by an election.
- *
- * @note All these functions play a significant role in the Recovery Phase,
- * which is triggered right after an election once someone becomes
- * the Leader.
- * @{
- */
- /**
- * Create a new Proposal Number and propose it to the Peons.
- *
- * This function starts the Recovery Phase, which can be directly mapped
- * onto the original Paxos' Prepare phase. Basically, we'll generate a
- * Proposal Number, taking @p oldpn into consideration, and we will send
- * it to a quorum, along with our first and last committed versions. By
- * sending these information in a message to the quorum, we expect to
- * obtain acceptances from a majority, allowing us to commit, or be
- * informed of a higher Proposal Number known by one or more of the Peons
- * in the quorum.
- *
- * @pre We are the Leader.
- * @post Recovery Phase initiated by sending messages to the quorum.
- *
- * @param oldpn A proposal number taken as the highest known so far, that
- * should be taken into consideration when generating a new
- * Proposal Number for the Recovery Phase.
- */
- void collect(version_t oldpn);
- /**
- * Handle the reception of a collect message from the Leader and reply
- * accordingly.
- *
- * Once a Peon receives a collect message from the Leader it will reply
- * with its first and last committed versions, as well as information so
- * the Leader may know if its Proposal Number was, or was not, accepted by
- * the Peon. The Peon will accept the Leader's Proposal Number if it is
- * higher than the Peon's currently accepted Proposal Number. The Peon may
- * also inform the Leader of accepted but uncommitted values.
- *
- * @invariant The message is an operation of type OP_COLLECT.
- * @pre We are a Peon.
- * @post Replied to the Leader, accepting or not accepting its PN.
- *
- * @param collect The collect message sent by the Leader to the Peon.
- */
- void handle_collect(MonOpRequestRef op);
- /**
- * Handle a response from a Peon to the Leader's collect phase.
- *
- * The received message will state the Peon's last committed version, as
- * well as its last proposal number. This will lead to one of the following
- * scenarios: if the replied Proposal Number is equal to the one we proposed,
- * then the Peon has accepted our proposal, and if all the Peons do accept
- * our Proposal Number, then we are allowed to proceed with the commit;
- * however, if a Peon replies with a higher Proposal Number, we assume he
- * knows something we don't and the Leader will have to abort the current
- * proposal in order to retry with the Proposal Number specified by the Peon.
- * It may also occur that the Peon replied with a lower Proposal Number, in
- * which case we assume it is a reply to an older value and we'll simply
- * drop it.
- * This function will also check if the Peon replied with an accepted but
- * yet uncommitted value. In this case, if its version is higher than our
- * last committed value by one, we assume that the Peon knows a value from a
- * previous proposal that has never been committed, and we should try to
- * commit that value by proposing it next. On the other hand, if that is
- * not the case, we'll assume it is an old, uncommitted value, we do not
- * care about and we'll consider the system active by extending the leases.
- *
- * @invariant The message is an operation of type OP_LAST.
- * @pre We are the Leader.
- * @post We initiate a commit, or we retry with a higher Proposal Number,
- * or we drop the message.
- * @post We move from STATE_RECOVERING to STATE_ACTIVE.
- *
- * @param last The message sent by the Peon to the Leader.
- */
- void handle_last(MonOpRequestRef op);
- /**
- * The Recovery Phase timed out, meaning that a significant part of the
- * quorum does not believe we are the Leader, and we thus should trigger new
- * elections.
- *
- * @pre We believe to be the Leader.
- * @post Trigger new elections.
- */
- void collect_timeout();
- /**
- * @}
- */
-
- /**
- * @defgroup Paxos_h_updating_funcs Functions used during the Updating State
- *
- * These functions may easily be mapped to the original Paxos Algorithm's
- * phases.
- *
- * Taking into account the algorithm can be divided in 4 phases (Prepare,
- * Promise, Accept Request and Accepted), we can easily map Paxos::begin to
- * both the Prepare and Accept Request phases; the Paxos::handle_begin to
- * the Promise phase; and the Paxos::handle_accept to the Accepted phase.
- * @{
- */
- /**
- * Start a new proposal with the intent of committing @p value.
- *
- * If we are alone on the system (i.e., a quorum of one), then we will
- * simply commit the value, but if we are not alone, then we need to propose
- * the value to the quorum.
- *
- * @pre We are the Leader
- * @pre We are on STATE_ACTIVE
- * @post We commit, if we are alone, or we send a message to each quorum
- * member
- * @post We are on STATE_ACTIVE, if we are alone, or on
- * STATE_UPDATING otherwise
- *
- * @param value The value being proposed to the quorum
- */
- void begin(bufferlist& value);
- /**
- * Accept or decline (by ignoring) a proposal from the Leader.
- *
- * We will decline the proposal (by ignoring it) if we have promised to
- * accept a higher numbered proposal. If that is not the case, we will
- * accept it and accordingly reply to the Leader.
- *
- * @pre We are a Peon
- * @pre We are on STATE_ACTIVE
- * @post We are on STATE_UPDATING if we accept the Leader's proposal
- * @post We send a reply message to the Leader if we accept its proposal
- *
- * @invariant The received message is an operation of type OP_BEGIN
- *
- * @param begin The message sent by the Leader to the Peon during the
- * Paxos::begin function
- *
- */
- void handle_begin(MonOpRequestRef op);
- /**
- * Handle an Accept message sent by a Peon.
- *
- * In order to commit, the Leader has to receive accepts from a majority of
- * the quorum. If that does happen, then the Leader may proceed with the
- * commit. However, the Leader needs the accepts from all the quorum members
- * in order to extend the lease and move on to STATE_ACTIVE.
- *
- * This function handles these two situations, accounting for the amount of
- * received accepts.
- *
- * @pre We are the Leader
- * @pre We are on STATE_UPDATING
- * @post We are on STATE_ACTIVE if we received accepts from the full quorum
- * @post We extended the lease if we moved on to STATE_ACTIVE
- * @post We are on STATE_UPDATING if we didn't received accepts from the
- * full quorum
- * @post We have committed if we received accepts from a majority
- *
- * @invariant The received message is an operation of type OP_ACCEPT
- *
- * @param accept The message sent by the Peons to the Leader during the
- * Paxos::handle_begin function
- */
- void handle_accept(MonOpRequestRef op);
- /**
- * Trigger a fresh election.
- *
- * During Paxos::begin we set a Callback of type Paxos::C_AcceptTimeout in
- * order to limit the amount of time we spend waiting for Accept replies.
- * This callback will call Paxos::accept_timeout when it is fired.
- *
- * This is essential to the algorithm because there may be the chance that
- * we are no longer the Leader (i.e., others don't believe in us) and we
- * are getting ignored, or we dropped out of the quorum and haven't realised
- * it. So, our only option is to trigger fresh elections.
- *
- * @pre We are the Leader
- * @pre We are on STATE_UPDATING
- * @post Triggered fresh elections
- */
- void accept_timeout();
- /**
- * @}
- */
-
-
- utime_t commit_start_stamp;
- friend struct C_Committed;
-
- /**
- * Commit a value throughout the system.
- *
- * The Leader will cancel the current lease (as it was for the old value),
- * and will store the committed value locally. It will then instruct every
- * quorum member to do so as well.
- *
- * @pre We are the Leader
- * @pre We are on STATE_UPDATING
- * @pre A majority of quorum members accepted our proposal
- * @post Value locally stored
- * @post Quorum members instructed to commit the new value.
- */
- void commit_start();
- void commit_finish(); ///< finish a commit after txn becomes durable
- void abort_commit(); ///< Handle commit finish after shutdown started
- /**
- * Commit the new value to stable storage as being the latest available
- * version.
- *
- * @pre We are a Peon
- * @post The new value is locally stored
- * @post Fire up the callbacks waiting on waiting_for_commit
- *
- * @invariant The received message is an operation of type OP_COMMIT
- *
- * @param commit The message sent by the Leader to the Peon during
- * Paxos::commit
- */
- void handle_commit(MonOpRequestRef op);
- /**
- * Extend the system's lease.
- *
- * This means that the Leader considers that it should now safe to read from
- * any node on the system, since every quorum member is now in possession of
- * the latest version. Therefore, the Leader will send a message stating just
- * this to each quorum member, and will impose a limited timeframe during
- * which acks will be accepted. If there aren't as many acks as expected
- * (i.e, if at least one quorum member does not ack the lease) during this
- * timeframe, then we will force fresh elections.
- *
- * @pre We are the Leader
- * @pre We are on STATE_ACTIVE
- * @post A message extending the lease is sent to each quorum member
- * @post A timeout callback is set to limit the amount of time we will wait
- * for lease acks.
- * @post A timer is set in order to renew the lease after a certain amount
- * of time.
- */
- void extend_lease();
- /**
- * Update the lease on the Peon's side of things.
- *
- * Once a Peon receives a Lease message, it will update its lease_expire
- * variable, reply to the Leader acknowledging the lease update and set a
- * timeout callback to be fired upon the lease's expiration. Finally, the
- * Peon will fire up all the callbacks waiting for it to become active,
- * which it just did, and all those waiting for it to become readable,
- * which should be true if the Peon's lease didn't expire in the mean time.
- *
- * @pre We are a Peon
- * @post We update the lease accordingly
- * @post A lease timeout callback is set
- * @post Move to STATE_ACTIVE
- * @post Fire up all the callbacks waiting for STATE_ACTIVE
- * @post Fire up all the callbacks waiting for readable if we are readable
- * @post Ack the lease to the Leader
- *
- * @invariant The received message is an operation of type OP_LEASE
- *
- * @param lease The message sent by the Leader to the Peon during the
- * Paxos::extend_lease function
- */
- void handle_lease(MonOpRequestRef op);
- /**
- * Account for all the Lease Acks the Leader receives from the Peons.
- *
- * Once the Leader receives all the Lease Acks from the Peons, it will be
- * able to cancel the Lease Ack timeout callback, thus avoiding calling
- * fresh elections.
- *
- * @pre We are the Leader
- * @post Cancel the Lease Ack timeout callback if we receive acks from all
- * the quorum members
- *
- * @invariant The received message is an operation of type OP_LEASE_ACK
- *
- * @param ack The message sent by a Peon to the Leader during the
- * Paxos::handle_lease function
- */
- void handle_lease_ack(MonOpRequestRef op);
- /**
- * Call fresh elections because at least one Peon didn't acked our lease.
- *
- * @pre We are the Leader
- * @pre We are on STATE_ACTIVE
- * @post Trigger fresh elections
- */
- void lease_ack_timeout();
- /**
- * Extend lease since we haven't had new committed values meanwhile.
- *
- * @pre We are the Leader
- * @pre We are on STATE_ACTIVE
- * @post Go through with Paxos::extend_lease
- */
- void lease_renew_timeout();
- /**
- * Call fresh elections because the Peon's lease expired without being
- * renewed or receiving a fresh lease.
- *
- * This means that the Peon is no longer assumed as being in the quorum
- * (or there is no Leader to speak of), so just trigger fresh elections
- * to circumvent this issue.
- *
- * @pre We are a Peon
- * @post Trigger fresh elections
- */
- void lease_timeout(); // on peon, if lease isn't extended
-
- /// restart the lease timeout timer
- void reset_lease_timeout();
-
- /**
- * Cancel all of Paxos' timeout/renew events.
- */
- void cancel_events();
- /**
- * Shutdown this Paxos machine
- */
- void shutdown();
-
- /**
- * Generate a new Proposal Number based on @p gt
- *
- * @todo Check what @p gt actually means and what its usage entails
- * @param gt A hint for the geration of the Proposal Number
- * @return A globally unique, monotonically increasing Proposal Number
- */
- version_t get_new_proposal_number(version_t gt=0);
-
- /**
- * @todo document sync function
- */
- void warn_on_future_time(utime_t t, entity_name_t from);
-
- /**
- * Begin proposing the pending_proposal.
- */
- void propose_pending();
-
- /**
- * refresh state from store
- *
- * Called when we have new state for the mon to consume. If we return false,
- * abort (we triggered a bootstrap).
- *
- * @returns true on success, false if we are now bootstrapping
- */
- bool do_refresh();
-
- void commit_proposal();
- void finish_round();
-
-public:
- /**
- * @param m A monitor
- * @param name A name for the paxos service. It serves as the naming space
- * of the underlying persistent storage for this service.
- */
- Paxos(Monitor *m, const string &name)
- : mon(m),
- logger(NULL),
- paxos_name(name),
- state(STATE_RECOVERING),
- first_committed(0),
- last_pn(0),
- last_committed(0),
- accepted_pn(0),
- accepted_pn_from(0),
- num_last(0),
- uncommitted_v(0), uncommitted_pn(0),
- collect_timeout_event(0),
- lease_renew_event(0),
- lease_ack_timeout_event(0),
- lease_timeout_event(0),
- accept_timeout_event(0),
- clock_drift_warned(0),
- trimming(false) { }
-
- const string get_name() const {
- return paxos_name;
- }
-
- void dispatch(MonOpRequestRef op);
-
- void read_and_prepare_transactions(MonitorDBStore::TransactionRef tx,
- version_t from, version_t last);
-
- void init();
-
- /**
- * dump state info to a formatter
- */
- void dump_info(Formatter *f);
-
- /**
- * This function runs basic consistency checks. Importantly, if
- * it is inconsistent and shouldn't be, it asserts out.
- *
- * @return True if consistent, false if not.
- */
- bool is_consistent();
-
- void restart();
- /**
- * Initiate the Leader after it wins an election.
- *
- * Once an election is won, the Leader will be initiated and there are two
- * possible outcomes of this method: the Leader directly jumps to the active
- * state (STATE_ACTIVE) if it believes to be the only one in the quorum, or
- * will start recovering (STATE_RECOVERING) by initiating the collect phase.
- *
- * @pre Our monitor is the Leader.
- * @post We are either on STATE_ACTIVE if we're the only one in the quorum,
- * or on STATE_RECOVERING otherwise.
- */
- void leader_init();
- /**
- * Initiate a Peon after it loses an election.
- *
- * If we are a Peon, then there must be a Leader and we are not alone in the
- * quorum, thus automatically assume we are on STATE_RECOVERING, which means
- * we will soon be enrolled into the Leader's collect phase.
- *
- * @pre There is a Leader, and it?s about to start the collect phase.
- * @post We are on STATE_RECOVERING and will soon receive collect phase's
- * messages.
- */
- void peon_init();
-
- /**
- * Include an incremental state of values, ranging from peer_first_committed
- * to the last committed value, on the message m
- *
- * @param m A message
- * @param peer_first_committed Lowest version to take into account
- * @param peer_last_committed Highest version to take into account
- */
- void share_state(MMonPaxos *m, version_t peer_first_committed,
- version_t peer_last_committed);
- /**
- * Store on disk a state that was shared with us
- *
- * Basically, we received a set of version. Or just one. It doesn't matter.
- * What matters is that we have to stash it in the store. So, we will simply
- * write every single bufferlist into their own versions on our side (i.e.,
- * onto paxos-related keys), and then we will decode those same bufferlists
- * we just wrote and apply the transactions they hold. We will also update
- * our first and last committed values to point to the new values, if need
- * be. All this is done tightly wrapped in a transaction to ensure we
- * enjoy the atomicity guarantees given by our awesome k/v store.
- *
- * @param m A message
- * @returns true if we stored something new; false otherwise
- */
- bool store_state(MMonPaxos *m);
- void _sanity_check_store();
-
- /**
- * Helper function to decode a bufferlist into a transaction and append it
- * to another transaction.
- *
- * This function is used during the Leader's commit and during the
- * Paxos::store_state in order to apply the bufferlist's transaction onto
- * the store.
- *
- * @param t The transaction to which we will append the operations
- * @param bl A bufferlist containing an encoded transaction
- */
- static void decode_append_transaction(MonitorDBStore::TransactionRef t,
- bufferlist& bl) {
- auto vt(std::make_shared<MonitorDBStore::Transaction>());
- bufferlist::iterator it = bl.begin();
- vt->decode(it);
- t->append(vt);
- }
-
- /**
- * @todo This appears to be used only by the OSDMonitor, and I would say
- * its objective is to allow a third-party to have a "private"
- * state dir. -JL
- */
- void add_extra_state_dir(string s) {
- extra_state_dirs.push_back(s);
- }
-
- // -- service interface --
- /**
- * Add c to the list of callbacks waiting for us to become active.
- *
- * @param c A callback
- */
- void wait_for_active(MonOpRequestRef op, Context *c) {
- if (op)
- op->mark_event("paxos:wait_for_active");
- waiting_for_active.push_back(c);
- }
- void wait_for_active(Context *c) {
- MonOpRequestRef o;
- wait_for_active(o, c);
- }
-
- /**
- * Trim the Paxos state as much as we can.
- */
- void trim();
-
- /**
- * Check if we should trim.
- *
- * If trimming is disabled, we must take that into consideration and only
- * return true if we are positively sure that we should trim soon.
- *
- * @returns true if we should trim; false otherwise.
- */
- bool should_trim() {
- int available_versions = get_version() - get_first_committed();
- int maximum_versions = g_conf->paxos_min + g_conf->paxos_trim_min;
-
- if (trimming || (available_versions <= maximum_versions))
- return false;
-
- return true;
- }
-
- bool is_plugged() const {
- return plugged;
- }
- void plug() {
- assert(plugged == false);
- plugged = true;
- }
- void unplug() {
- assert(plugged == true);
- plugged = false;
- }
-
- // read
- /**
- * @defgroup Paxos_h_read_funcs Read-related functions
- * @{
- */
- /**
- * Get latest committed version
- *
- * @return latest committed version
- */
- version_t get_version() { return last_committed; }
- /**
- * Get first committed version
- *
- * @return the first committed version
- */
- version_t get_first_committed() { return first_committed; }
- /**
- * Get the last commit time
- *
- * @returns Our last commit time
- */
- utime_t get_last_commit_time() const{
- return last_commit_time;
- }
- /**
- * Check if a given version is readable.
- *
- * A version may not be readable for a myriad of reasons:
- * @li the version @e v is higher that the last committed version
- * @li we are not the Leader nor a Peon (election may be on-going)
- * @li we do not have a committed value yet
- * @li we do not have a valid lease
- *
- * @param seen The version we want to check if it is readable.
- * @return 'true' if the version is readable; 'false' otherwise.
- */
- bool is_readable(version_t seen=0);
- /**
- * Read version @e v and store its value in @e bl
- *
- * @param[in] v The version we want to read
- * @param[out] bl The version's value
- * @return 'true' if we successfully read the value; 'false' otherwise
- */
- bool read(version_t v, bufferlist &bl);
- /**
- * Read the latest committed version
- *
- * @param[out] bl The version's value
- * @return the latest committed version if we successfully read the value;
- * or 0 (zero) otherwise.
- */
- version_t read_current(bufferlist &bl);
- /**
- * Add onreadable to the list of callbacks waiting for us to become readable.
- *
- * @param onreadable A callback
- */
- void wait_for_readable(MonOpRequestRef op, Context *onreadable) {
- assert(!is_readable());
- if (op)
- op->mark_event("paxos:wait_for_readable");
- waiting_for_readable.push_back(onreadable);
- }
- void wait_for_readable(Context *onreadable) {
- MonOpRequestRef o;
- wait_for_readable(o, onreadable);
- }
- /**
- * @}
- */
-
- /**
- * Check if we have a valid lease.
- *
- * @returns true if the lease is still valid; false otherwise.
- */
- bool is_lease_valid();
- // write
- /**
- * @defgroup Paxos_h_write_funcs Write-related functions
- * @{
- */
- /**
- * Check if we are writeable.
- *
- * We are writeable if we are alone (i.e., a quorum of one), or if we match
- * all the following conditions:
- * @li We are the Leader
- * @li We are on STATE_ACTIVE
- * @li We have a valid lease
- *
- * @return 'true' if we are writeable; 'false' otherwise.
- */
- bool is_writeable();
- /**
- * Add c to the list of callbacks waiting for us to become writeable.
- *
- * @param c A callback
- */
- void wait_for_writeable(MonOpRequestRef op, Context *c) {
- assert(!is_writeable());
- if (op)
- op->mark_event("paxos:wait_for_writeable");
- waiting_for_writeable.push_back(c);
- }
- void wait_for_writeable(Context *c) {
- MonOpRequestRef o;
- wait_for_writeable(o, c);
- }
-
- /**
- * Get a transaction to submit operations to propose against
- *
- * Apply operations to this transaction. It will eventually be proposed
- * to paxos.
- */
- MonitorDBStore::TransactionRef get_pending_transaction();
-
- /**
- * Queue a completion for the pending proposal
- *
- * This completion will get triggered when the pending proposal
- * transaction commits.
- */
- void queue_pending_finisher(Context *onfinished);
-
- /**
- * (try to) trigger a proposal
- *
- * Tell paxos that it should submit the pending proposal. Note that if it
- * is not active (e.g., because it is already in the midst of committing
- * something) that will be deferred (e.g., until the current round finishes).
- */
- bool trigger_propose();
-
- /**
- * Add oncommit to the back of the list of callbacks waiting for us to
- * finish committing.
- *
- * @param oncommit A callback
- */
- void wait_for_commit(Context *oncommit) {
- waiting_for_commit.push_back(oncommit);
- }
- /**
- * Add oncommit to the front of the list of callbacks waiting for us to
- * finish committing.
- *
- * @param oncommit A callback
- */
- void wait_for_commit_front(Context *oncommit) {
- waiting_for_commit.push_front(oncommit);
- }
- /**
- * @}
- */
-
- /**
- * @}
- */
- protected:
- MonitorDBStore *get_store();
-};
-
-inline ostream& operator<<(ostream& out, Paxos::C_Proposal& p)
-{
- string proposed = (p.proposed ? "proposed" : "unproposed");
- out << " " << proposed
- << " queued " << (ceph_clock_now() - p.proposal_time)
- << " tx dump:\n";
- auto t(std::make_shared<MonitorDBStore::Transaction>());
- bufferlist::iterator p_it = p.bl.begin();
- t->decode(p_it);
- JSONFormatter f(true);
- t->dump(&f);
- f.flush(out);
- return out;
-}
-
-#endif
-