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/* This file is part of VoltDB.
* Copyright (C) 2008-2020 VoltDB Inc.
*
* This program is free software: you can redistribute it and/or modify
* it under the terms of the GNU Affero General Public License as
* published by the Free Software Foundation, either version 3 of the
* License, or (at your option) any later version.
*
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU Affero General Public License for more details.
*
* You should have received a copy of the GNU Affero General Public License
* along with VoltDB. If not, see .
*/
package org.voltcore.agreement;
import static com.google_voltpatches.common.base.Predicates.in;
import static com.google_voltpatches.common.base.Predicates.not;
import java.util.Iterator;
import java.util.Map;
import java.util.Map.Entry;
import java.util.Set;
import org.voltcore.messaging.FaultMessage;
import org.voltcore.messaging.SiteFailureForwardMessage;
import org.voltcore.messaging.SiteFailureMessage;
import org.voltcore.utils.CoreUtils;
import org.voltcore.utils.Pair;
import com.google_voltpatches.common.base.Predicate;
import com.google_voltpatches.common.collect.ImmutableSet;
import com.google_voltpatches.common.collect.ImmutableSortedSet;
import com.google_voltpatches.common.collect.Maps;
import com.google_voltpatches.common.collect.Multimap;
import com.google_voltpatches.common.collect.Multimaps;
import com.google_voltpatches.common.collect.Sets;
import com.google_voltpatches.common.collect.TreeMultimap;
public class AgreementSeeker {
protected final ArbitrationStrategy m_strategy;
/** hsid of the site holding this instance */
protected final long m_selfHsid;
/** mesh hsids before agreement is sought */
protected Set m_hsids;
/** the set of hsids which this site can see */
protected Set m_survivors;
/**
* graph where each key is a site, and their corresponding values are sites
* that have reported it
*/
protected final TreeMultimap m_reported = TreeMultimap.create();
/**
* graph were each key denotes a site, and their corresponding values are sites
* that see it dead
*/
protected final TreeMultimap m_dead = TreeMultimap.create();
/**
* graph were each key denotes a site, and their corresponding values are sites
* that see it alive
*/
protected final TreeMultimap m_alive = TreeMultimap.create();
public AgreementSeeker(final ArbitrationStrategy strategy, long selfHsid) {
m_strategy = strategy;
m_selfHsid = selfHsid;
m_hsids = ImmutableSet.of();
m_survivors = ImmutableSet.of();
}
/**
* Start accumulate site links graphing information
*
* @param hsids pre-failure mesh hsids
* @param inTrouble a map where each key is a failed site, and its value is
* a boolean that indicates whether or not the failure was witnessed directly
* or reported by some other site
*/
public void startSeekingFor(
final Set hsids, final Map inTrouble) {
// if the mesh hsids change we need to reset
if (!m_hsids.equals(hsids)) {
if (!m_hsids.isEmpty()) clear();
m_hsids = ImmutableSortedSet.copyOf(hsids);
}
// determine the survivors
m_survivors = m_strategy.accept(survivorPicker, Pair.of(m_hsids, inTrouble));
// start accumulating link failure graphing info
add(m_selfHsid, inTrouble);
}
public void clear() {
m_reported.clear();
m_dead.clear();
m_alive.clear();
m_hsids = ImmutableSet.of();
m_survivors = ImmutableSet.of();
}
/**
* Convenience method that remove all instances of the given values
* from the given map
* @param mm a multimap
* @param values a set of values that need to be removed
*/
static protected void removeValues(TreeMultimap mm, Set values) {
Iterator> itr = mm.entries().iterator();
while (itr.hasNext()) {
Map.Entry e = itr.next();
if (values.contains(e.getValue())) {
itr.remove();
}
}
}
/**
* a visitor that accepts a pair consisting of pre-failure mesh hsids,
* and its failed sites map, and returns a set of survivors
*/
static protected final ArbitrationStrategy.Visitor, Pair, Map>> survivorPicker =
new ArbitrationStrategy.Visitor, Pair,Map>>() {
@Override
public Set visitMatchingCardinality(Pair, Map> p) {
Set dead =
Maps.filterEntries(p.getSecond(), amongDeadHsids(p.getFirst())).keySet();
return ImmutableSortedSet.copyOf(Sets.difference(p.getFirst(), dead));
}
@Override
public Set visitNoQuarter(Pair, Map> p) {
Set reported = Maps.filterKeys(p.getSecond(), in(p.getFirst())).keySet();
return ImmutableSortedSet.copyOf(Sets.difference(p.getFirst(), reported));
}
};
/**
* returns a map entry predicate that tests whether or not the given
* map entry describes a dead site
* @param hsids pre-failure mesh hsids
* @return
*/
public static Predicate> amongDeadHsids(final Set hsids) {
return new Predicate>() {
@Override
public boolean apply(Entry e) {
return hsids.contains(e.getKey()) && e.getValue();
}
};
}
/**
* a site predicate that tests whether or not a site is
* among the set of survivors
*/
public final Predicate amongSurvivors = new Predicate() {
@Override
public boolean apply(Long site) {
return m_survivors.contains(site);
}
};
/**
* returns the current set of survivors
* @return the current set of survivors
*/
public Set getSurvivors() {
return m_survivors;
}
/**
* Convenience method that remove all instances of the given value
* from the given map
* @param mm a multimap
* @param value a value that needs to be removed
*/
private void removeValue(TreeMultimap mm, long value) {
Iterator> itr = mm.entries().iterator();
while (itr.hasNext()) {
Map.Entry e = itr.next();
if (e.getValue().equals(value)) {
itr.remove();
}
}
}
protected String dumpGraph(Multimap mm, StringBuilder sb) {
sb.append("{ ");
int count = 0;
for (long h: mm.keySet()) {
if (count++ > 0) sb.append(", ");
sb.append(CoreUtils.hsIdToString(h)).append(": [");
sb.append(CoreUtils.hsIdCollectionToString(mm.get(h)));
sb.append("]");
}
sb.append("}");
return sb.toString();
}
public String dumpAlive() {
StringBuilder sb = new StringBuilder();
sb.append("Alive: ");
dumpGraph(m_alive, sb);
return sb.toString();
}
public String dumpDead() {
StringBuilder sb = new StringBuilder();
sb.append("Dead: ");
dumpGraph(m_dead, sb);
return sb.toString();
}
public String dumpReported() {
StringBuilder sb = new StringBuilder();
sb.append("Reported: ");
dumpGraph(m_reported, sb);
return sb.toString();
}
public String dumpSurvivors() {
StringBuilder sb = new StringBuilder();
sb.append("Survivor: ");
sb.append("{ ");
int count = 0;
for (Long hsId : m_survivors) {
if (count++ > 0) sb.append(", ");
sb.append(CoreUtils.hsIdToString(hsId));
}
sb.append(" }");
return sb.toString();
}
/**
* Adds alive and dead graph information
* @param reportingHsid site reporting failures
* @param failures seen by the reporting site
*/
void add(long reportingHsid, final Map failed) {
// skip if the reporting site did not belong to the pre
// failure mesh
if (!m_hsids.contains(reportingHsid)) return;
// ship if the reporting site is reporting itself dead
Boolean harakiri = failed.get(reportingHsid);
if (harakiri != null && harakiri.booleanValue()) return;
Set dead = Sets.newHashSet();
for (Map.Entry e: failed.entrySet()) {
// skip if the failed site did not belong to the
// pre failure mesh
if (!m_hsids.contains(e.getKey())) continue;
m_reported.put(e.getKey(), reportingHsid);
// if the failure is witnessed add it to the dead graph
if (e.getValue()) {
m_dead.put(e.getKey(), reportingHsid);
dead.add(e.getKey());
}
}
// once you are witnessed dead you cannot become undead,
// but it is not the case for alive nodes, as they can
// die. So remove all what the reporting site thought
// was alive before this invocation
removeValue(m_alive, reportingHsid);
for (Long alive: Sets.difference(m_hsids, dead)) {
m_alive.put(alive, reportingHsid);
}
}
/**
* Adds alive and dead graph information from a reporting
* site survivor set
* @param reportingHsid the reporting site
* @param sfm a {@link SiteFailureMessage} containing that
* site's survivor set
*/
public void add(long reportingHsid, SiteFailureMessage sfm) {
// skip if the reporting site did not belong to the pre
// failure mesh, or the reporting site is reporting itself
// dead, or none of the sites in the safe transaction map
// are among the known hsids
if ( !m_hsids.contains(reportingHsid)
|| !sfm.m_survivors.contains(reportingHsid)) return;
Set survivors = sfm.m_survivors;
if (Sets.filter(sfm.getObservedFailedSites(), in(m_hsids)).isEmpty()) {
survivors = m_hsids;
}
// dead = pre failure mesh - survivors
Set dead = Sets.difference(m_hsids, survivors);
removeValue(m_dead, reportingHsid);
// add dead graph nodes
for (long w: dead) {
if (!m_hsids.contains(w)) continue;
m_dead.put(w,reportingHsid);
}
// Remove all what the reporting site thought
// was alive before this invocation
removeValue(m_alive, reportingHsid);
// add alive graph nodes
for (long s: survivors) {
if (!m_hsids.contains(s)) continue;
m_alive.put(s, reportingHsid);
}
for (long s: sfm.getFailedSites()) {
if (!m_hsids.contains(s)) continue;
m_reported.put(s, reportingHsid);
}
}
/**
* Adds alive and dead graph information from a reporting
* site survivor set
* @param sfm a {@link SiteFailureMessage} containing that
* site's survivor set
*/
public void add(SiteFailureMessage sfm) {
add(sfm.m_sourceHSId, sfm);
}
/**
* Adds alive and dead graph information from a reporting
* site survivor set
* @param reportingHsid the reporting site
* @param sfm a {@link SiteFailureForwardMessage} containing that
* site's survivor set
*/
public void add(SiteFailureForwardMessage fsfm) {
add(fsfm.m_reportingHSId,fsfm);
}
/**
* Does the given graph scenario meet the criteria of
* having reached an agreement?
* @param sc a graph scenario
*/
protected Boolean haveAgreement(Scenario sc) {
return m_strategy.accept(agreementSeeker, sc);
}
/**
* a visitor that accepts a graph scenario and returns whether or not
* the graph scenario has reached an agreement
*/
protected final ArbitrationStrategy.Visitor agreementSeeker =
new ArbitrationStrategy.Visitor() {
@Override
public Boolean visitNoQuarter(Scenario sc) {
Iterator itr = sc.reported.keySet().iterator();
boolean agree = true;
while (agree && itr.hasNext()) {
agree = sc.reported.get(itr.next()).containsAll(sc.survivors);
}
return agree;
}
/**
* a quorum is comprised of sites that the given scenario
* has left alive. This returns true if each dead node in
* the scenario is seen dead by all in the quorum
*/
@Override
public Boolean visitMatchingCardinality(Scenario sc) {
boolean agree = true;
Set quorum = Sets.intersection(sc.alive.keySet(),sc.survivors);
for (Long dead: sc.dead.keySet()) {
agree = agree && quorum.equals(sc.dead.get(dead));
}
return agree;
}
};
public boolean needForward(int [] countdown) {
return --countdown[0] > 0 && m_strategy.accept(forwardDemander, (Void)null);
}
/**
* Is anyone in the mesh alive and connected to sites I consider dead?
*/
public boolean needForward() {
return m_strategy.accept(forwardDemander, (Void)null);
}
/**
* a visitor that tests whether or not there is a connected path
* between myself and any site I consider dead
*/
protected ArbitrationStrategy.Visitor forwardDemander =
new ArbitrationStrategy.Visitor() {
@Override
public Boolean visitNoQuarter(Void nads) {
return false;
}
/**
* Tests whether or not there is a connected path between myself,
* and any site I consider dead
* @param nada
* @return true if there are peer sites that can tell me about
* sites that I consider dead
*/
@Override
public Boolean visitMatchingCardinality(Void nada) {
if (m_survivors.size() == 1) return false;
Set unreachable = Sets.filter(m_hsids, not(in(m_survivors)));
Set butAlive = Sets.intersection(m_alive.keySet(), unreachable);
return !butAlive.isEmpty()
&& seenByInterconnectedPeers(butAlive, Sets.newTreeSet(m_survivors))
&& !m_dead.get(m_selfHsid).containsAll(butAlive);
}
};
/**
* Walk the alive graph to see if there is a connected path between origins,
* and destinations
* @param destinations set of sites that we are looking a path to
* @param origins set of sites that we are looking a path from
* @return true origins have path to destinations
*/
protected boolean seenByInterconnectedPeers( Set destinations, Set origins) {
Set seers = Multimaps.filterValues(m_alive, in(origins)).keySet();
int before = origins.size();
origins.addAll(seers);
if (origins.containsAll(destinations)) {
return true;
} else if (origins.size() == before) {
return false;
}
return seenByInterconnectedPeers(destinations, origins);
}
/**
* Determine the set of nodes to kill to accomplish a fully connected
* mesh with the remaining sites
* @return a set of nodes to kill
*/
public Set nextKill() {
return m_strategy.accept(killPicker, m_selfHsid);
}
protected ArbitrationStrategy.Visitor, Long> killPicker =
new ArbitrationStrategy.Visitor, Long>() {
@Override
public Set visitNoQuarter(Long self) {
return ImmutableSet.copyOf(m_reported.keySet());
}
// if a is picked then you need to remove all alive by (a)
// and add them to dead
// alive(a) is c,d,e,f now dead(a) += alive(a)
// you also have to remove all (a)'s from deadBy values,
// as (a) can no longer see anyone dead or alive
/**
* This strategy picks first the sites that are considered
* dead by most of the remaining sites, and for ties breakers
* it picks the sites with highest hsids
* @param self the invoking site hsid
* @return a set of nodes to kill
*/
@Override
public Set visitMatchingCardinality(Long self) {
Set picks = Sets.newHashSet();
Scenario sc = new Scenario();
while (!haveAgreement(sc)) {
Long pick = null;
for (Long s: sc.dead.keySet()) {
// cannot pick self or the ones already picked
if (s.equals(self) || picks.contains(s)) continue;
Set deadBy = sc.dead.get(s);
if (deadBy.isEmpty()) continue;
if (pick != null) {
int cmp = deadBy.size()
- sc.dead.get(pick).size();
if (cmp > 0 || (cmp == 0 && s.compareTo(pick) > 0)) {
pick = s;
}
} else {
pick = s;
}
}
if (pick == null) {
/*
* You only get here if and ONLY if yourself are the ONLY viable kill
*/
return ImmutableSet.of();/*ImmutableSet.copyOf(
Sets.filter(m_hsids, not(equalTo(m_selfHsid))));*/
}
// pick can no longer see anyone dead or alive
removeValue(sc.dead,pick);
removeValue(sc.alive, pick);
sc.dead.putAll(pick, sc.alive.removeAll(pick));
picks.add(pick);
}
return ImmutableSet.copyOf(sc.dead.keySet());
}
};
/**
* Is the given hsid considered dead by anyone in my survivor set?
* @param hsid a site hsid
* @return a subset of my survivor set that considers the given site dead
*/
public Set forWhomSiteIsDead(long hsid) {
ImmutableSet.Builder isb = ImmutableSet.builder();
Set deadBy = m_dead.get(hsid);
if ( !deadBy.isEmpty()
&& m_survivors.contains(hsid)
&& m_strategy == ArbitrationStrategy.MATCHING_CARDINALITY) {
isb.addAll(Sets.filter(deadBy, amongSurvivors));
}
return isb.build();
}
public long bestKillCandidateAmong(Set candidates) {
long pick = Long.MIN_VALUE;
int dings = Integer.MIN_VALUE;
for (long candidate: candidates) {
int siteDings = m_dead.get(candidate).size();
if (siteDings > dings) {
dings = siteDings;
pick = candidate;
} else if (dings == siteDings && candidate > pick) {
pick = candidate;
}
}
return pick;
}
public boolean alreadyKnow(FaultMessage fm) {
for (Long survivor : fm.survivors) {
// Do we already know all the survivors?
if (!m_alive.get(survivor).contains(fm.reportingSite)) {
return false;
}
}
// Do we already know the dead?
if (!m_dead.get(fm.failedSite).contains(fm.reportingSite)) {
return false;
}
// Nothing new!! No need to report to fault resolver.
return true;
}
@Override
public String toString() {
StringBuilder sb = new StringBuilder();
sb.append("AgreementSeeker { hsId: ").append(CoreUtils.hsIdToString(m_selfHsid));
sb.append(", survivors: [").append(CoreUtils.hsIdCollectionToString(m_survivors));
sb.append("], alive: ");
dumpGraph(m_alive, sb);
sb.append(", dead: ");
dumpGraph(m_dead, sb);
sb.append("}");
return sb.toString();
}
protected class Scenario {
protected TreeMultimap reported;
protected TreeMultimap dead;
protected TreeMultimap alive;
protected Set survivors;
protected Scenario() {
reported = TreeMultimap.create(m_reported);
dead = TreeMultimap.create(m_dead);
survivors = Sets.newTreeSet(m_survivors);
alive = TreeMultimap.create(m_alive);
}
}
}
