// repl.cpp

/* TODO
   PAIRING
    _ on a syncexception, don't allow going back to master state?
*/

/**
*    Copyright (C) 2008 10gen Inc.
*
*    This program is free software: you can redistribute it and/or  modify
*    it under the terms of the GNU Affero General Public License, version 3,
*    as published by the Free Software Foundation.
*
*    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 this program.  If not, see <http://www.gnu.org/licenses/>.
*/

/* Collections we use:

   local.sources         - indicates what sources we pull from as a "slave", and the last update of each
   local.oplog.$main     - our op log as "master"
   local.dbinfo.<dbname>
   local.pair.startup    - can contain a special value indicating for a pair that we have the master copy.
                           used when replacing other half of the pair which has permanently failed.
   local.pair.sync       - { initialsynccomplete: 1 }
*/

#include "pch.h"
#include "jsobj.h"
#include "../util/goodies.h"
#include "repl.h"
#include "../util/message.h"
#include "../util/background.h"
#include "../client/dbclient.h"
#include "../client/connpool.h"
#include "pdfile.h"
#include "query.h"
#include "db.h"
#include "commands.h"
#include "security.h"
#include "cmdline.h"
#include "repl_block.h"
#include "repl/rs.h"

namespace mongo {
    
    // our config from command line etc.
    ReplSettings replSettings;

    /* if 1 sync() is running */
    volatile int syncing = 0;
	static volatile int relinquishSyncingSome = 0;

    /* if true replace our peer in a replication pair -- don't worry about if his
       local.oplog.$main is empty.
    */
    bool replacePeer = false;

    /* "dead" means something really bad happened like replication falling completely out of sync.
       when non-null, we are dead and the string is informational
    */
    const char *replAllDead = 0;

    time_t lastForcedResync = 0;
    
    IdTracker &idTracker = *( new IdTracker() );
    
} // namespace mongo

#include "replpair.h"

namespace mongo {

    PairSync *pairSync = new PairSync();
    bool getInitialSyncCompleted() {
        return pairSync->initialSyncCompleted();
    }

    /* --- ReplPair -------------------------------- */

    ReplPair *replPair = 0;

    /* output by the web console */
    const char *replInfo = "";
    struct ReplInfo {
        ReplInfo(const char *msg) {
            replInfo = msg;
        }
        ~ReplInfo() {
            replInfo = "?";
        }
    };

    void ReplPair::setMaster(int n, const char *_comment ) {
        if ( n == State_Master && !getInitialSyncCompleted() )
            return;
        info = _comment;
        if ( n != state && !cmdLine.quiet )
            tlog() << "pair: setting master=" << n << " was " << state << endl;
        state = n;
    }

    /* peer unreachable, try our arbiter */
    void ReplPair::arbitrate() {
        ReplInfo r("arbitrate");

        if ( arbHost == "-" ) {
            // no arbiter. we are up, let's assume partner is down and network is not partitioned.
            setMasterLocked(State_Master, "remote unreachable");
            return;
        }

        auto_ptr<DBClientConnection> conn( newClientConnection() );
        string errmsg;
        if ( !conn->connect(arbHost.c_str(), errmsg) ) {
            tlog() << "repl:   cantconn arbiter " << errmsg << endl;
            setMasterLocked(State_CantArb, "can't connect to arb");
            return;
        }

        negotiate( conn.get(), "arbiter" );
    }

    /* --------------------------------------------- */

    class CmdReplacePeer : public Command {
    public:
        virtual bool slaveOk() const {
            return true;
        }
        virtual bool adminOnly() const {
            return true;
        }
        virtual LockType locktype() const { return WRITE; }
        void help(stringstream&h) const { h << "replace a node in a replica pair"; }
        CmdReplacePeer() : Command("replacePeer", false, "replacepeer") { }
        virtual bool run(const string& , BSONObj& cmdObj, string& errmsg, BSONObjBuilder& result, bool fromRepl) {
            if ( replPair == 0 ) {
                errmsg = "not paired";
                return false;
            }
            if ( !getInitialSyncCompleted() ) {
                errmsg = "not caught up cannot replace peer";
                return false;
            }
            if ( syncing < 0 ) {
                errmsg = "replacepeer already invoked";
                return false;
            }
            Timer t;
            while ( 1 ) {
                if ( syncing == 0 || t.millis() > 30000 )
                    break;
                {
                    dbtemprelease t;
					relinquishSyncingSome = 1;
					sleepmillis(1);
                }
            }
            if ( syncing ) {
                assert( syncing > 0 );
                errmsg = "timeout waiting for sync() to finish";
                return false;
            }
            {
                ReplSource::SourceVector sources;
                ReplSource::loadAll(sources);
                if ( sources.size() != 1 ) {
                    errmsg = "local.sources.count() != 1, cannot replace peer";
                    return false;
                }
            }
            {
                Helpers::emptyCollection("local.sources");
                BSONObj o = fromjson("{\"replacepeer\":1}");
                Helpers::putSingleton("local.pair.startup", o);
            }
            syncing = -1;
            replAllDead = "replacepeer invoked -- adjust local.sources hostname then restart this db process";
            result.append("info", "adjust local.sources hostname; db restart now required");
            return true;
        }
    } cmdReplacePeer;

    class CmdForceDead : public Command {
    public:
        virtual bool slaveOk() const {
            return true;
        }
        virtual bool adminOnly() const {
            return true;
        }
        virtual void help(stringstream& h) const { h << "internal"; }
        virtual LockType locktype() const { return WRITE; }
        CmdForceDead() : Command("forcedead") { }
        virtual bool run(const string& , BSONObj& cmdObj, string& errmsg, BSONObjBuilder& result, bool fromRepl) {
            replAllDead = "replication forced to stop by 'forcedead' command";
            log() << "*********************************************************\n";
            log() << "received 'forcedead' command, replication forced to stop" << endl;
            return true;
        }
    } cmdForceDead;
    
    /* operator requested resynchronization of replication (on the slave).  { resync : 1 } */
    class CmdResync : public Command {
    public:
        virtual bool slaveOk() const {
            return true;
        }
        virtual bool adminOnly() const {
            return true;
        }
        virtual bool logTheOp() { return false; }
        virtual LockType locktype() const { return WRITE; }
        void help(stringstream&h) const { h << "resync (from scratch) an out of date replica slave.\nhttp://www.mongodb.org/display/DOCS/Master+Slave"; }
        CmdResync() : Command("resync") { }
        virtual bool run(const string& , BSONObj& cmdObj, string& errmsg, BSONObjBuilder& result, bool fromRepl) {
            if ( cmdObj.getBoolField( "force" ) ) {
                if ( !waitForSyncToFinish( errmsg ) )
                    return false;
                replAllDead = "resync forced";
            }            
            if ( !replAllDead ) {
                errmsg = "not dead, no need to resync";
                return false;
            }
            if ( !waitForSyncToFinish( errmsg ) )
                return false;
            
            ReplSource::forceResyncDead( "client" );
            result.append( "info", "triggered resync for all sources" );
            return true;                
        }        
        bool waitForSyncToFinish( string &errmsg ) const {
            // Wait for slave thread to finish syncing, so sources will be be
            // reloaded with new saved state on next pass.
            Timer t;
            while ( 1 ) {
                if ( syncing == 0 || t.millis() > 30000 )
                    break;
                {
                    dbtemprelease t;
					relinquishSyncingSome = 1;
                    sleepmillis(1);
                }
            }
            if ( syncing ) {
                errmsg = "timeout waiting for sync() to finish";
                return false;
            }
            return true;
        }
    } cmdResync;
    
    bool anyReplEnabled(){
        return replPair || replSettings.slave || replSettings.master;
    }

    void appendReplicationInfo( BSONObjBuilder& result , bool authed , int level ){
        
        if ( replAllDead ) {
            result.append("ismaster", 0);
            if( authed ) { 
                if ( replPair )
                    result.append("remote", replPair->remote);
            }
            string s = string("dead: ") + replAllDead;
            result.append("info", s);
        }
        else if ( replPair ) {
            result.append("ismaster", replPair->state);
            if( authed ) {
                result.append("remote", replPair->remote);
                if ( !replPair->info.empty() )
                    result.append("info", replPair->info.toString());
            }
        }
        else {
            result.appendBool("ismaster", _isMaster() );
        }

        if ( level && replSet ){
            result.append( "info" , "is replica set" );
        }
        else if ( level ){
            BSONObjBuilder sources( result.subarrayStart( "sources" ) );
            
            readlock lk( "local.sources" );
            Client::Context ctx( "local.sources" );
            shared_ptr<Cursor> c = findTableScan("local.sources", BSONObj());
            int n = 0;
            while ( c->ok() ){
                BSONObj s = c->current();
                
                BSONObjBuilder bb;
                bb.append( s["host"] );
                string sourcename = s["source"].valuestr();
                if ( sourcename != "main" )
                    bb.append( s["source"] );
                
                {
                    BSONElement e = s["syncedTo"];
                    BSONObjBuilder t( bb.subobjStart( "syncedTo" ) );
                    t.appendDate( "time" , e.timestampTime() );
                    t.append( "inc" , e.timestampInc() );
                    t.done();
                }
                
                if ( level > 1 ){
                    dbtemprelease unlock;
                    ScopedDbConnection conn( s["host"].valuestr() );
                    BSONObj first = conn->findOne( (string)"local.oplog.$" + sourcename , Query().sort( BSON( "$natural" << 1 ) ) );
                    BSONObj last = conn->findOne( (string)"local.oplog.$" + sourcename , Query().sort( BSON( "$natural" << -1 ) ) );
                    bb.appendDate( "masterFirst" , first["ts"].timestampTime() );
                    bb.appendDate( "masterLast" , last["ts"].timestampTime() );
                    double lag = (double) (last["ts"].timestampTime() - s["syncedTo"].timestampTime());
                    bb.append( "lagSeconds" , lag / 1000 );
                    conn.done();
                }

                sources.append( BSONObjBuilder::numStr( n++ ) , bb.obj() );
                c->advance();
            }
            
            sources.done();
        }
    }

    class CmdIsMaster : public Command {
    public:
        virtual bool requiresAuth() { return false; }
        virtual bool slaveOk() const {
            return true;
        }
        virtual void help( stringstream &help ) const {
            help << "Check if this server is primary for a replica pair/set; also if it is --master or --slave in simple master/slave setups.\n";
            help << "{ isMaster : 1 }";
        }
        virtual LockType locktype() const { return NONE; }
        CmdIsMaster() : Command("isMaster", true, "ismaster") { }
        virtual bool run(const string& , BSONObj& cmdObj, string& errmsg, BSONObjBuilder& result, bool /*fromRepl*/) {
			/* currently request to arbiter is (somewhat arbitrarily) an ismaster request that is not 
			   authenticated.
			   we allow unauthenticated ismaster but we aren't as verbose informationally if 
			   one is not authenticated for admin db to be safe.
			*/

            if( replSet ) {
                if( theReplSet == 0 ) { 
                    result.append("ismaster", false);
                    result.append("secondary", false);
                    errmsg = "replSet still trying to initialize";
                    result.append("info", ReplSet::startupStatusMsg);
                    return true;
                }
                theReplSet->fillIsMaster(result);
                return true;
            }
            
			bool authed = cc().getAuthenticationInfo()->isAuthorizedReads("admin");
            appendReplicationInfo( result , authed );
            return true;
        }
    } cmdismaster;

    class CmdIsInitialSyncComplete : public Command {
    public:
        virtual bool requiresAuth() { return false; }
        virtual bool slaveOk() const {
            return true;
        }
        virtual LockType locktype() const { return WRITE; }
        CmdIsInitialSyncComplete() : Command( "isinitialsynccomplete" ) {}
        virtual bool run(const string&, BSONObj& cmdObj, string& errmsg, BSONObjBuilder& result, bool /*fromRepl*/) {
            result.appendBool( "initialsynccomplete", getInitialSyncCompleted() );
            return true;
        }
    } cmdisinitialsynccomplete;
    
    /* negotiate who is master

       -1=not set (probably means we just booted)
        0=was slave
        1=was master

       remote,local -> new remote,local
       !1,1  -> 0,1
       1,!1  -> 1,0
       -1,-1 -> dominant->1, nondom->0
       0,0   -> dominant->1, nondom->0
       1,1   -> dominant->1, nondom->0

       { negotiatemaster:1, i_was:<state>, your_name:<hostname> }
       returns:
       { ok:1, you_are:..., i_am:... }
    */
    class CmdNegotiateMaster : public Command {
    public:
        CmdNegotiateMaster() : Command("negotiatemaster") { }
        virtual bool slaveOk() const {
            return true;
        }
        virtual bool adminOnly() const {
            return true;
        }
        virtual LockType locktype() const { return WRITE; }
        virtual bool run(const string& , BSONObj& cmdObj, string& errmsg, BSONObjBuilder& result, bool) {
            if ( replPair == 0 ) {
                massert( 10383 ,  "Another mongod instance believes incorrectly that this node is its peer", !cmdObj.getBoolField( "fromArbiter" ) );
                // assume that we are an arbiter and should forward the request
                string host = cmdObj.getStringField("your_name");
                int port = cmdObj.getIntField( "your_port" );
                if ( port == INT_MIN ) {
                    errmsg = "no port specified";
                    problem() << errmsg << endl;
                    return false;
                }
                stringstream ss;
                ss << host << ":" << port;
                string remote = ss.str();
                BSONObj ret;
                {
                    dbtemprelease t;
                    auto_ptr<DBClientConnection> conn( new DBClientConnection() );
                    if ( !conn->connect( remote.c_str(), errmsg ) ) {
                        result.append( "you_are", ReplPair::State_Master );
                        return true;
                    }
                    BSONObjBuilder forwardCommand;
                    forwardCommand.appendElements( cmdObj );
                    forwardCommand.appendBool( "fromArbiter", true );
                    ret = conn->findOne( "admin.$cmd", forwardCommand.done() );
                }
                BSONObjIterator i( ret );
                while( i.moreWithEOO() ) {
                    BSONElement e = i.next();
                    if ( e.eoo() )
                        break;
                    if ( e.fieldName() != string( "ok" ) )
                        result.append( e );
                }
                return ret["ok"].trueValue();
            }

            int was = cmdObj.getIntField("i_was");
            string myname = cmdObj.getStringField("your_name");
            if ( myname.empty() || was < -3 ) {
                errmsg = "your_name/i_was not specified";
                return false;
            }

            int N = ReplPair::State_Negotiating;
            int M = ReplPair::State_Master;
            int S = ReplPair::State_Slave;

            if ( !replPair->dominant( myname ) ) {
                result.append( "you_are", N );
                result.append( "i_am", replPair->state );
                return true;
            }

            int me, you;
            if ( !getInitialSyncCompleted() || ( replPair->state != M && was == M ) ) {
                me=S;
                you=M;
            }
            else {
                me=M;
                you=S;
            }
            replPair->setMaster( me, "CmdNegotiateMaster::run()" );

            result.append("you_are", you);
            result.append("i_am", me);

            return true;
        }
    } cmdnegotiatemaster;
    
    int ReplPair::negotiate(DBClientConnection *conn, string method) {
        BSONObjBuilder b;
        b.append("negotiatemaster",1);
        b.append("i_was", state);
        b.append("your_name", remoteHost);
        b.append("your_port", remotePort);
        BSONObj cmd = b.done();
        BSONObj res = conn->findOne("admin.$cmd", cmd);
        if ( ! res["ok"].trueValue() ){
            string message = method + " negotiate failed";
            problem() << message << ": " << res.toString() << '\n';
            setMasterLocked(State_Confused, message.c_str());
            return State_Confused;
        }
        int x = res.getIntField("you_are");
        int remote = res.getIntField("i_am");
        // State_Negotiating means the remote node is not dominant and cannot
        // choose who is master.
        if ( x != State_Slave && x != State_Master && x != State_Negotiating ) {
            problem() << method << " negotiate: bad you_are value " << res.toString() << endl;
        } else if ( x != State_Negotiating ) {
            string message = method + " negotiation";
            setMasterLocked(x, message.c_str());
        }
        return remote;
    }

    /* --------------------------------------------------------------*/

    ReplSource::ReplSource() {
        replacing = false;
        nClonedThisPass = 0;
        paired = false;
    }

    ReplSource::ReplSource(BSONObj o) : nClonedThisPass(0) {
        replacing = false;
        paired = false;
        only = o.getStringField("only");
        hostName = o.getStringField("host");
        _sourceName = o.getStringField("source");
        uassert( 10118 ,  "'host' field not set in sources collection object", !hostName.empty() );
        uassert( 10119 ,  "only source='main' allowed for now with replication", sourceName() == "main" );
        BSONElement e = o.getField("syncedTo");
        if ( !e.eoo() ) {
            uassert( 10120 ,  "bad sources 'syncedTo' field value", e.type() == Date || e.type() == Timestamp );
            OpTime tmp( e.date() );
            syncedTo = tmp;
        }

        BSONObj dbsObj = o.getObjectField("dbsNextPass");
        if ( !dbsObj.isEmpty() ) {
            BSONObjIterator i(dbsObj);
            while ( 1 ) {
                BSONElement e = i.next();
                if ( e.eoo() )
                    break;
                addDbNextPass.insert( e.fieldName() );
            }
        }        
        
        dbsObj = o.getObjectField("incompleteCloneDbs");
        if ( !dbsObj.isEmpty() ) {
            BSONObjIterator i(dbsObj);
            while ( 1 ) {
                BSONElement e = i.next();
                if ( e.eoo() )
                    break;
                incompleteCloneDbs.insert( e.fieldName() );
            }
        }        

        _lastSavedLocalTs = OpTime( o.getField( "localLogTs" ).date() );
    }

    /* Turn our C++ Source object into a BSONObj */
    BSONObj ReplSource::jsobj() {
        BSONObjBuilder b;
        b.append("host", hostName);
        b.append("source", sourceName());
        if ( !only.empty() )
            b.append("only", only);
        if ( !syncedTo.isNull() )
            b.appendTimestamp("syncedTo", syncedTo.asDate());

        b.appendTimestamp("localLogTs", _lastSavedLocalTs.asDate());
        
        BSONObjBuilder dbsNextPassBuilder;
        int n = 0;
        for ( set<string>::iterator i = addDbNextPass.begin(); i != addDbNextPass.end(); i++ ) {
            n++;
            dbsNextPassBuilder.appendBool(*i, 1);
        }
        if ( n )
            b.append("dbsNextPass", dbsNextPassBuilder.done());

        BSONObjBuilder incompleteCloneDbsBuilder;
        n = 0;
        for ( set<string>::iterator i = incompleteCloneDbs.begin(); i != incompleteCloneDbs.end(); i++ ) {
            n++;
            incompleteCloneDbsBuilder.appendBool(*i, 1);
        }
        if ( n )
            b.append("incompleteCloneDbs", incompleteCloneDbsBuilder.done());

        return b.obj();
    }

    void ReplSource::save() {
        BSONObjBuilder b;
        assert( !hostName.empty() );
        b.append("host", hostName);
        // todo: finish allowing multiple source configs.
        // this line doesn't work right when source is null, if that is allowed as it is now:
        //b.append("source", _sourceName);
        BSONObj pattern = b.done();

        BSONObj o = jsobj();
        log( 1 ) << "Saving repl source: " << o << endl;

        {
            OpDebug debug;
            Client::Context ctx("local.sources");
            UpdateResult res = updateObjects("local.sources", o, pattern, true/*upsert for pair feature*/, false,false,debug);
            assert( ! res.mod );
            assert( res.num == 1 );
        }

        if ( replacing ) {
            /* if we were in "replace" mode, we now have synced up with the replacement,
               so turn that off.
               */
            replacing = false;
            wassert( replacePeer );
            replacePeer = false;
            Helpers::emptyCollection("local.pair.startup");
        }
    }

    static void addSourceToList(ReplSource::SourceVector &v, ReplSource& s, const BSONObj &spec, ReplSource::SourceVector &old) {
        if ( !s.syncedTo.isNull() ) { // Don't reuse old ReplSource if there was a forced resync.
            for ( ReplSource::SourceVector::iterator i = old.begin(); i != old.end();  ) {
                if ( s == **i ) {
                    v.push_back(*i);
                    old.erase(i);
                    return;
                }
                i++;
            }
        }

        v.push_back( shared_ptr< ReplSource >( new ReplSource( s ) ) );
    }

    /* we reuse our existing objects so that we can keep our existing connection
       and cursor in effect.
    */
    void ReplSource::loadAll(SourceVector &v) {
        Client::Context ctx("local.sources");
        SourceVector old = v;
        v.clear();

        bool gotPairWith = false;

        if ( !cmdLine.source.empty() ) {
            // --source <host> specified.
            // check that no items are in sources other than that
            // add if missing
            shared_ptr<Cursor> c = findTableScan("local.sources", BSONObj());
            int n = 0;
            while ( c->ok() ) {
                n++;
                ReplSource tmp(c->current());
                if ( tmp.hostName != cmdLine.source ) {
                    log() << "repl: --source " << cmdLine.source << " != " << tmp.hostName << " from local.sources collection" << endl;
                    log() << "repl: terminating mongod after 30 seconds" << endl;
                    sleepsecs(30);
                    dbexit( EXIT_REPLICATION_ERROR );
                }
                if ( tmp.only != cmdLine.only ) {
                    log() << "--only " << cmdLine.only << " != " << tmp.only << " from local.sources collection" << endl;
                    log() << "terminating after 30 seconds" << endl;
                    sleepsecs(30);
                    dbexit( EXIT_REPLICATION_ERROR );
                }
                c->advance();
            }
            uassert( 10002 ,  "local.sources collection corrupt?", n<2 );
            if ( n == 0 ) {
                // source missing.  add.
                ReplSource s;
                s.hostName = cmdLine.source;
                s.only = cmdLine.only;
                s.save();
            }
        }
        else {
            try {
                massert( 10384 , "--only requires use of --source", cmdLine.only.empty());
            } catch ( ... ) {
                dbexit( EXIT_BADOPTIONS );
            }
        }
        
        if ( replPair ) {
            const string &remote = replPair->remote;
            // --pairwith host specified.
            if ( replSettings.fastsync ) {
                Helpers::emptyCollection( "local.sources" );  // ignore saved sources
            }
            // check that no items are in sources other than that
            // add if missing
            shared_ptr<Cursor> c = findTableScan("local.sources", BSONObj());
            int n = 0;
            while ( c->ok() ) {
                n++;
                ReplSource tmp(c->current());
                if ( tmp.hostName != remote ) {
                    log() << "pairwith " << remote << " != " << tmp.hostName << " from local.sources collection" << endl;
                    log() << "terminating after 30 seconds" << endl;
                    sleepsecs(30);
                    dbexit( EXIT_REPLICATION_ERROR );
                }
                c->advance();
            }
            uassert( 10122 ,  "local.sources collection corrupt?", n<2 );
            if ( n == 0 ) {
                // source missing.  add.
                ReplSource s;
                s.hostName = remote;
                s.save();
            }
        }

        shared_ptr<Cursor> c = findTableScan("local.sources", BSONObj());
        while ( c->ok() ) {
            ReplSource tmp(c->current());
            if ( replPair && tmp.hostName == replPair->remote && tmp.sourceName() == "main" ) {
                gotPairWith = true;
                tmp.paired = true;
                if ( replacePeer ) {
                    // peer was replaced -- start back at the beginning.
                    tmp.syncedTo = OpTime();
                    tmp.replacing = true;
                }
            } 
            if ( ( !replPair && tmp.syncedTo.isNull() ) ||
                ( replPair && replSettings.fastsync ) ) {
                DBDirectClient c;
                if ( c.exists( "local.oplog.$main" ) ) {
                    BSONObj op = c.findOne( "local.oplog.$main", QUERY( "op" << NE << "n" ).sort( BSON( "$natural" << -1 ) ) );
                    if ( !op.isEmpty() ) {
                        tmp.syncedTo = op[ "ts" ].date();
                        tmp._lastSavedLocalTs = op[ "ts" ].date();
                    }
                }
            }
            addSourceToList(v, tmp, c->current(), old);
            c->advance();
        }

        if ( !gotPairWith && replPair ) {
            /* add the --pairwith server */
            shared_ptr< ReplSource > s( new ReplSource() );
            s->paired = true;
            s->hostName = replPair->remote;
            s->replacing = replacePeer;
            v.push_back(s);
        }
    }

    BSONObj opTimeQuery = fromjson("{\"getoptime\":1}");

    bool ReplSource::throttledForceResyncDead( const char *requester ) {
        if ( time( 0 ) - lastForcedResync > 600 ) {
            forceResyncDead( requester );
            lastForcedResync = time( 0 );
            return true;
        }
        return false;
    }
    
    void ReplSource::forceResyncDead( const char *requester ) {
        if ( !replAllDead )
            return;
        SourceVector sources;
        ReplSource::loadAll(sources);
        for( SourceVector::iterator i = sources.begin(); i != sources.end(); ++i ) {
            (*i)->forceResync( requester );
        }
        replAllDead = 0;        
    }
    
    void ReplSource::forceResync( const char *requester ) {
        BSONObj info;
        {
            dbtemprelease t;
            oplogReader.connect(hostName);
            /* todo use getDatabaseNames() method here */
            bool ok = oplogReader.conn()->runCommand( "admin", BSON( "listDatabases" << 1 ), info );
            massert( 10385 ,  "Unable to get database list", ok );
        }
        BSONObjIterator i( info.getField( "databases" ).embeddedObject() );
        while( i.moreWithEOO() ) {
            BSONElement e = i.next();
            if ( e.eoo() )
                break;
            string name = e.embeddedObject().getField( "name" ).valuestr();
            if ( !e.embeddedObject().getBoolField( "empty" ) ) {
                if ( name != "local" ) {
                    if ( only.empty() || only == name ) {
                        resyncDrop( name.c_str(), requester );
                    }
                }
            }
        }        
        syncedTo = OpTime();
        addDbNextPass.clear();
        save();
    }

    string ReplSource::resyncDrop( const char *db, const char *requester ) {
        log() << "resync: dropping database " << db << endl;
        Client::Context ctx(db);
        dropDatabase(db);
        return db;
    }
    
    /* grab initial copy of a database from the master */
    bool ReplSource::resync(string db) {
        string dummyNs = resyncDrop( db.c_str(), "internal" );
        Client::Context ctx( dummyNs );
        {
            log() << "resync: cloning database " << db << " to get an initial copy" << endl;
            ReplInfo r("resync: cloning a database");
            string errmsg;
            bool ok = cloneFrom(hostName.c_str(), errmsg, cc().database()->name, false, /*slaveok*/ true, /*replauth*/ true, /*snapshot*/false);
            if ( !ok ) {
                problem() << "resync of " << db << " from " << hostName << " failed " << errmsg << endl;
                throw SyncException();
            }
        }

        log() << "resync: done with initial clone for db: " << db << endl;

        return true;
    }

    void ReplSource::applyOperation(const BSONObj& op) {
        try {
            applyOperation_inlock( op );
        }
        catch ( UserException& e ) {
            log() << "sync: caught user assertion " << e << " while applying op: " << op << endl;;
        }
        catch ( DBException& e ) {
            log() << "sync: caught db exception " << e << " while applying op: " << op << endl;;            
        }

    }

    /* local.$oplog.main is of the form:
         { ts: ..., op: <optype>, ns: ..., o: <obj> , o2: <extraobj>, b: <boolflag> }
         ...
       see logOp() comments.
    */
    void ReplSource::sync_pullOpLog_applyOperation(BSONObj& op, OpTime *localLogTail) {
        if( logLevel >= 6 ) // op.tostring is expensive so doing this check explicitly
            log(6) << "processing op: " << op << endl;

        if( op.getStringField("op")[0] == 'n' )
            return;

        char clientName[MaxDatabaseLen];
        const char *ns = op.getStringField("ns");
        nsToDatabase(ns, clientName);

        if ( *ns == '.' ) {
            problem() << "skipping bad op in oplog: " << op.toString() << endl;
            return;
        }
        else if ( *ns == 0 ) {
            problem() << "halting replication, bad op in oplog:\n  " << op.toString() << endl;
            replAllDead = "bad object in oplog";
            throw SyncException();
        }

        if ( !only.empty() && only != clientName )
            return;

        if( cmdLine.pretouch ) {
            if( cmdLine.pretouch > 1 ) {
                /* note: this is bad - should be put in ReplSource.  but this is first test... */
                static int countdown;
                if( countdown > 0 ) {
                    countdown--; // was pretouched on a prev pass
                    assert( countdown >= 0 );
                } else {
                    const int m = 4;
                    if( tp.get() == 0 ) {
                        int nthr = min(8, cmdLine.pretouch);
                        nthr = max(nthr, 1);
                        tp.reset( new ThreadPool(nthr) );
                    }
                    vector<BSONObj> v;
                    oplogReader.peek(v, cmdLine.pretouch);
                    unsigned a = 0;
                    while( 1 ) {
                        if( a >= v.size() ) break;
                        unsigned b = a + m - 1; // v[a..b]
                        if( b >= v.size() ) b = v.size() - 1;
                        tp->schedule(pretouchN, v, a, b);
                        DEV cout << "pretouch task: " << a << ".." << b << endl;
                        a += m;
                    }
                    // we do one too...
                    pretouchOperation(op);
                    tp->join();
                    countdown = v.size();
                }
            }
            else {
                pretouchOperation(op);
            }
        }

        dblock lk;

        if ( localLogTail && replPair && replPair->state == ReplPair::State_Master ) {
            updateSetsWithLocalOps( *localLogTail, true ); // allow unlocking
            updateSetsWithLocalOps( *localLogTail, false ); // don't allow unlocking or conversion to db backed storage
        }

        if ( replAllDead ) {
            // hmmm why is this check here and not at top of this function? does it get set between top and here?
            log() << "replAllDead, throwing SyncException: " << replAllDead << endl;
            throw SyncException();
        }
        
        Client::Context ctx( ns );
        ctx.getClient()->curop()->reset();

        bool empty = ctx.db()->isEmpty();
        bool incompleteClone = incompleteCloneDbs.count( clientName ) != 0;

        if( logLevel >= 6 )
            log(6) << "ns: " << ns << ", justCreated: " << ctx.justCreated() << ", empty: " << empty << ", incompleteClone: " << incompleteClone << endl;
        
        // always apply admin command command
        // this is a bit hacky -- the semantics of replication/commands aren't well specified
        if ( strcmp( clientName, "admin" ) == 0 && *op.getStringField( "op" ) == 'c' ) {
            applyOperation( op );
            return;
        }
        
        if ( ctx.justCreated() || empty || incompleteClone ) {
            // we must add to incomplete list now that setClient has been called
            incompleteCloneDbs.insert( clientName );
            if ( nClonedThisPass ) {
                /* we only clone one database per pass, even if a lot need done.  This helps us
                 avoid overflowing the master's transaction log by doing too much work before going
                 back to read more transactions. (Imagine a scenario of slave startup where we try to
                 clone 100 databases in one pass.)
                 */
                addDbNextPass.insert( clientName );
            } else {
                if ( incompleteClone ) {
                    log() << "An earlier initial clone of '" << clientName << "' did not complete, now resyncing." << endl;
                }
                save();
                Client::Context ctx(ns);
                nClonedThisPass++;
                resync(ctx.db()->name);
                addDbNextPass.erase(clientName);
                incompleteCloneDbs.erase( clientName );
            }
            save();
        } else {
            bool mod;
            if ( replPair && replPair->state == ReplPair::State_Master ) {
                BSONObj id = idForOp( op, mod );
                if ( !idTracker.haveId( ns, id ) ) {
                    applyOperation( op );    
                } else if ( idTracker.haveModId( ns, id ) ) {
                    log( 6 ) << "skipping operation matching mod id object " << op << endl;
                    BSONObj existing;
                    if ( Helpers::findOne( ns, id, existing ) )
                        logOp( "i", ns, existing );
                } else {
                    log( 6 ) << "skipping operation matching changed id object " << op << endl;
                }
            } else {
                applyOperation( op );
            }
            addDbNextPass.erase( clientName );
        }
    }

    BSONObj ReplSource::idForOp( const BSONObj &op, bool &mod ) {
        mod = false;
        const char *opType = op.getStringField( "op" );
        BSONObj o = op.getObjectField( "o" );
        switch( opType[ 0 ] ) {
            case 'i': {
                BSONObjBuilder idBuilder;
                BSONElement id;
                if ( !o.getObjectID( id ) )
                    return BSONObj();                    
                idBuilder.append( id );
                return idBuilder.obj();
            }
            case 'u': {
                BSONObj o2 = op.getObjectField( "o2" );
                if ( strcmp( o2.firstElement().fieldName(), "_id" ) != 0 )
                    return BSONObj();
                if ( o.firstElement().fieldName()[ 0 ] == '$' )
                    mod = true;
                return o2;
            }
            case 'd': {
                if ( opType[ 1 ] != '\0' )
                    return BSONObj(); // skip "db" op type
                return o;
            }
            default:
                break;
        }        
        return BSONObj();
    }
    
    void ReplSource::updateSetsWithOp( const BSONObj &op, bool mayUnlock ) {
        if ( mayUnlock ) {
            idTracker.mayUpgradeStorage();
        }
        bool mod;
        BSONObj id = idForOp( op, mod );
        if ( !id.isEmpty() ) {
            const char *ns = op.getStringField( "ns" );
            // Since our range of local ops may not be the same as our peer's
            // range of unapplied ops, it is always necessary to rewrite objects
            // to the oplog after a mod update.
            if ( mod )
                idTracker.haveModId( ns, id, true );
            idTracker.haveId( ns, id, true );
        }        
    }
    
    void ReplSource::syncToTailOfRemoteLog() {
        string _ns = ns();
        BSONObjBuilder b;
        if ( !only.empty() ) {
            b.appendRegex("ns", string("^") + only);
        }        
        BSONObj last = oplogReader.findOne( _ns.c_str(), Query( b.done() ).sort( BSON( "$natural" << -1 ) ) );
        if ( !last.isEmpty() ) {
            BSONElement ts = last.getField( "ts" );
            massert( 10386 ,  "non Date ts found: " + last.toString(), ts.type() == Date || ts.type() == Timestamp );
            syncedTo = OpTime( ts.date() );
        }        
    }
    
    OpTime ReplSource::nextLastSavedLocalTs() const {
        Client::Context ctx( "local.oplog.$main" );
        shared_ptr<Cursor> c = findTableScan( "local.oplog.$main", BSON( "$natural" << -1 ) );
        if ( c->ok() )
            return OpTime( c->current().getField( "ts" ).date() );        
        return OpTime();
    }
    
    void ReplSource::setLastSavedLocalTs( const OpTime &nextLocalTs ) {
        _lastSavedLocalTs = nextLocalTs;
        log( 3 ) << "updated _lastSavedLocalTs to: " << _lastSavedLocalTs << endl;
    }
    
    void ReplSource::resetSlave() {
        log() << "**********************************************************\n";
        log() << "Sending forcedead command to slave to stop its replication\n";
        log() << "Host: " << hostName << " paired: " << paired << endl;
        massert( 10387 ,  "request to kill slave replication failed",
                oplogReader.conn()->simpleCommand( "admin", 0, "forcedead" ) );
        syncToTailOfRemoteLog();
        {
            dblock lk;
            setLastSavedLocalTs( nextLastSavedLocalTs() );
            save();
            oplogReader.resetCursor();
        }
    }
    
    bool ReplSource::updateSetsWithLocalOps( OpTime &localLogTail, bool mayUnlock ) {
        Client::Context ctx( "local.oplog.$main" );
        shared_ptr<Cursor> localLog = findTableScan( "local.oplog.$main", BSON( "$natural" << -1 ) );
        OpTime newTail;
        for( ; localLog->ok(); localLog->advance() ) {
            BSONObj op = localLog->current();
            OpTime ts( localLog->current().getField( "ts" ).date() );
            if ( newTail.isNull() ) {
                newTail = ts;
            }
            if ( !( localLogTail < ts ) )
                break;
            updateSetsWithOp( op, mayUnlock );
            if ( mayUnlock ) {
                RARELY {
                    dbtemprelease t;
                }
            }
        }
        if ( !localLogTail.isNull() && !localLog->ok() ) {
            // local log filled up
            idTracker.reset();
            dbtemprelease t;
            resetSlave();
            massert( 10388 ,  "local master log filled, forcing slave resync", false );
        }        
        if ( !newTail.isNull() )
            localLogTail = newTail;
        return true;
    }
    
    /* slave: pull some data from the master's oplog
       note: not yet in db mutex at this point. 
       @return -1 error
               0 ok, don't sleep
               1 ok, sleep
    */
    int ReplSource::sync_pullOpLog(int& nApplied) {
        int okResultCode = 1;
        string ns = string("local.oplog.$") + sourceName();
        log(2) << "repl: sync_pullOpLog " << ns << " syncedTo:" << syncedTo.toStringLong() << '\n';

        bool tailing = true;
        oplogReader.tailCheck();

        if ( replPair && replPair->state == ReplPair::State_Master ) {
            dblock lk;
            idTracker.reset();
        }
        OpTime localLogTail = _lastSavedLocalTs;

        bool initial = syncedTo.isNull();
        
        if ( !oplogReader.haveCursor() || initial ) {
            if ( initial ) {
                // Important to grab last oplog timestamp before listing databases.
                syncToTailOfRemoteLog();
                BSONObj info;
                bool ok = oplogReader.conn()->runCommand( "admin", BSON( "listDatabases" << 1 ), info );
                massert( 10389 ,  "Unable to get database list", ok );
                BSONObjIterator i( info.getField( "databases" ).embeddedObject() );
                while( i.moreWithEOO() ) {
                    BSONElement e = i.next();
                    if ( e.eoo() )
                        break;
                    string name = e.embeddedObject().getField( "name" ).valuestr();
                    if ( !e.embeddedObject().getBoolField( "empty" ) ) {
                        if ( name != "local" ) {
                            if ( only.empty() || only == name ) {
                                log( 2 ) << "adding to 'addDbNextPass': " << name << endl;
                                addDbNextPass.insert( name );
                            }
                        }
                    }
                }
                dblock lk;
                save();
            }
                        
            BSONObjBuilder q;
            q.appendDate("$gte", syncedTo.asDate());
            BSONObjBuilder query;
            query.append("ts", q.done());
            if ( !only.empty() ) {
               // note we may here skip a LOT of data table scanning, a lot of work for the master.
                query.appendRegex("ns", string("^") + only); // maybe append "\\." here?
            }
            BSONObj queryObj = query.done();
            // e.g. queryObj = { ts: { $gte: syncedTo } }

            oplogReader.tailingQuery(ns.c_str(), queryObj);
            tailing = false;
        }
        else {
            log(2) << "repl: tailing=true\n";
        }

        if( !oplogReader.haveCursor() ) {
            problem() << "repl: dbclient::query returns null (conn closed?)" << endl;
            oplogReader.resetConnection();
            return -1;
        }

        // show any deferred database creates from a previous pass
        {
            set<string>::iterator i = addDbNextPass.begin();
            if ( i != addDbNextPass.end() ) {
                BSONObjBuilder b;
                b.append("ns", *i + '.');
                b.append("op", "db");
                BSONObj op = b.done();
                sync_pullOpLog_applyOperation(op, 0);
            }
        }

        if ( !oplogReader.more() ) {
            if ( tailing ) {
                log(2) << "repl: tailing & no new activity\n";
                if( oplogReader.awaitCapable() )
                    okResultCode = 0; // don't sleep

            } else {
                log() << "repl:   " << ns << " oplog is empty\n";
            }
            {
                dblock lk;
                OpTime nextLastSaved = nextLastSavedLocalTs();
                {
                    dbtemprelease t;
                    if ( !oplogReader.more() ) {
                        setLastSavedLocalTs( nextLastSaved );
                    }
                }
                save();            
            }
            return okResultCode;
        }
        
        OpTime nextOpTime;
        {
            BSONObj op = oplogReader.next();
            BSONElement ts = op.getField("ts");
            if ( ts.type() != Date && ts.type() != Timestamp ) {
                string err = op.getStringField("$err");
                if ( !err.empty() ) {
                    // 13051 is "tailable cursor requested on non capped collection"
                    if (op.getIntField("code") == 13051) {
                        problem() << "trying to slave off of a non-master" << '\n';
                        massert( 13344 ,  "trying to slave off of a non-master", false );
                    }
                    else {
                        problem() << "repl: $err reading remote oplog: " + err << '\n';
                        massert( 10390 ,  "got $err reading remote oplog", false );
                    }
                }
                else {
                    problem() << "repl: bad object read from remote oplog: " << op.toString() << '\n';
                    massert( 10391 , "repl: bad object read from remote oplog", false);
                }
            }
        
            if ( replPair && replPair->state == ReplPair::State_Master ) {
            
                OpTime next( ts.date() );
                if ( !tailing && !initial && next != syncedTo ) {
                    log() << "remote slave log filled, forcing slave resync" << endl;
                    resetSlave();
                    return 1;
                }            
            
                dblock lk;
                updateSetsWithLocalOps( localLogTail, true );
            }
        
            nextOpTime = OpTime( ts.date() );
            log(2) << "repl: first op time received: " << nextOpTime.toString() << '\n';
            if ( tailing || initial ) {
                if ( initial )
                    log(1) << "repl:   initial run\n";
                else {
                    if( !( syncedTo <= nextOpTime ) ) { 
                        log() << "repl ASSERTION failed : syncedTo <= nextOpTime" << endl;
                        log() << "repl syncTo:     " << syncedTo.toStringLong() << endl;
                        log() << "repl nextOpTime: " << nextOpTime.toStringLong() << endl;
                        assert(false);
                    }
                }
                oplogReader.putBack( op ); // op will be processed in the loop below
                nextOpTime = OpTime(); // will reread the op below
            }
            else if ( nextOpTime != syncedTo ) { // didn't get what we queried for - error
                Nullstream& l = log();
                l << "repl:   nextOpTime " << nextOpTime.toStringLong() << ' ';
                if ( nextOpTime < syncedTo )
                    l << "<??";
                else
                    l << ">";

                l << " syncedTo " << syncedTo.toStringLong() << '\n';
                log() << "repl:   time diff: " << (nextOpTime.getSecs() - syncedTo.getSecs()) << "sec\n";
                log() << "repl:   tailing: " << tailing << '\n';
                log() << "repl:   data too stale, halting replication" << endl;
                replInfo = replAllDead = "data too stale halted replication";
                assert( syncedTo < nextOpTime );
                throw SyncException();
            }
            else {
                /* t == syncedTo, so the first op was applied previously. */
            }
        }

        // apply operations
        {
            int n = 0;
			time_t saveLast = time(0);
            while ( 1 ) {
                /* from a.s.:
                   I think the idea here is that we can establish a sync point between the local op log and the remote log with the following steps:

                   1) identify most recent op in local log -- call it O
                   2) ask "does nextOpTime reflect the tail of the remote op log?" (in other words, is more() false?) - If yes, all subsequent ops after nextOpTime in the remote log must have occurred after O.  If no, we can't establish a sync point.

                   Note that we can't do step (2) followed by step (1) because if we do so ops may be added to both machines between steps (2) and (1) and we can't establish a sync point.  (In particular, between (2) and (1) an op may be added to the remote log before a different op is added to the local log.  In this case, the newest remote op will have occurred after nextOpTime but before O.)

                   Now, for performance reasons we don't want to have to identify the most recent op in the local log every time we call c->more() because in performance sensitive situations more() will be true most of the time.  So we do:

                   0) more()?
                   1) find most recent op in local log
                   2) more()?
                */

                bool moreInitialSyncsPending = !addDbNextPass.empty() && n; // we need "&& n" to assure we actually process at least one op to get a sync point recorded in the first place.

                if ( moreInitialSyncsPending || !oplogReader.more() ) {
                    dblock lk;
                    OpTime nextLastSaved = nextLastSavedLocalTs();
                    {
                        dbtemprelease t;
                        if ( !moreInitialSyncsPending && oplogReader.more() ) {
                            if ( getInitialSyncCompleted() ) { // if initial sync hasn't completed, break out of loop so we can set to completed or clone more dbs
                                continue;
                            }
                        } else {
                            setLastSavedLocalTs( nextLastSaved );
                        }
                    }
                    if( oplogReader.awaitCapable() && tailing )
                        okResultCode = 0; // don't sleep
                    syncedTo = nextOpTime;
                    save(); // note how far we are synced up to now
                    log() << "repl:   applied " << n << " operations" << endl;
                    nApplied = n;
                    log() << "repl:  end sync_pullOpLog syncedTo: " << syncedTo.toStringLong() << endl;
                    break;
                }
                else {
                }

                OCCASIONALLY if( n > 0 && ( n > 100000 || time(0) - saveLast > 60 ) ) { 
					// periodically note our progress, in case we are doing a lot of work and crash
					dblock lk;
                    syncedTo = nextOpTime;
                    // can't update local log ts since there are pending operations from our peer
					save();
                    log() << "repl:   checkpoint applied " << n << " operations" << endl;
                    log() << "repl:   syncedTo: " << syncedTo.toStringLong() << endl;
					saveLast = time(0);
					n = 0;
				}

                BSONObj op = oplogReader.next();
                BSONElement ts = op.getField("ts");
                if( !( ts.type() == Date || ts.type() == Timestamp ) ) { 
                    log() << "sync error: problem querying remote oplog record\n";
                    log() << "op: " << op.toString() << '\n';
                    log() << "halting replication" << endl;
                    replInfo = replAllDead = "sync error: no ts found querying remote oplog record";
                    throw SyncException();
                }
                OpTime last = nextOpTime;
                nextOpTime = OpTime( ts.date() );
                if ( !( last < nextOpTime ) ) {
                    log() << "sync error: last applied optime at slave >= nextOpTime from master" << endl;
                    log() << " last:       " << last.toStringLong() << '\n';
                    log() << " nextOpTime: " << nextOpTime.toStringLong() << '\n';
                    log() << " halting replication" << endl;
                    replInfo = replAllDead = "sync error last >= nextOpTime";
                    uassert( 10123 , "replication error last applied optime at slave >= nextOpTime from master", false);
                }
                if ( replSettings.slavedelay && ( unsigned( time( 0 ) ) < nextOpTime.getSecs() + replSettings.slavedelay ) ) {
                    oplogReader.putBack( op );
                    _sleepAdviceTime = nextOpTime.getSecs() + replSettings.slavedelay + 1;
                    dblock lk;
                    if ( n > 0 ) {
                        syncedTo = last;
                        save();
                    }
                    log() << "repl:   applied " << n << " operations" << endl;
                    log() << "repl:   syncedTo: " << syncedTo.toStringLong() << endl;
                    log() << "waiting until: " << _sleepAdviceTime << " to continue" << endl;
                    break;
                }

                sync_pullOpLog_applyOperation(op, &localLogTail);
                n++;
            }
        }

        return okResultCode;
    }

	BSONObj userReplQuery = fromjson("{\"user\":\"repl\"}");
    
	bool replAuthenticate(DBClientConnection *conn) {
		if( ! cc().isAdmin() ){
			log() << "replauthenticate: requires admin permissions, failing\n";
			return false;
		}

		BSONObj user;
		{
			dblock lk;
			Client::Context ctxt("local.");
			if( !Helpers::findOne("local.system.users", userReplQuery, user) ) { 
				// try the first user is local
				if( !Helpers::getSingleton("local.system.users", user) ) {
					if( noauth ) 
						return true; // presumably we are running a --noauth setup all around.

					log() << "replauthenticate: no user in local.system.users to use for authentication\n";
					return false;
				}
			}
            
		}

		string u = user.getStringField("user");
		string p = user.getStringField("pwd");
		massert( 10392 , "bad user object? [1]", !u.empty());
		massert( 10393 , "bad user object? [2]", !p.empty());
		string err;
		if( !conn->auth("local", u.c_str(), p.c_str(), err, false) ) {
			log() << "replauthenticate: can't authenticate to master server, user:" << u << endl;
			return false;
		}
		return true;
	}

    bool replHandshake(DBClientConnection *conn) {
        
        BSONObj me;
        {
            dblock l;
            if ( ! Helpers::getSingleton( "local.me" , me ) ){
                BSONObjBuilder b;
                b.appendOID( "_id" , 0 , true );
                me = b.obj();
                Helpers::putSingleton( "local.me" , me );
            }
        }
        
        BSONObjBuilder cmd;
        cmd.appendAs( me["_id"] , "handshake" );

        BSONObj res;
        bool ok = conn->runCommand( "admin" , cmd.obj() , res );
        // ignoring for now on purpose for older versions
        log(ok) << "replHandshake res not: " << ok << " res: " << res << endl;
        return true;
    }

    bool OplogReader::connect(string hostName) {
        if( conn() == 0 ) {
            _conn = auto_ptr<DBClientConnection>(new DBClientConnection( false, 0, replPair ? 20 : 0 /* tcp timeout */));
            string errmsg;
            ReplInfo r("trying to connect to sync source");
            if ( !_conn->connect(hostName.c_str(), errmsg) || 
                 !replAuthenticate(_conn.get()) ||
                 !replHandshake(_conn.get()) ) {
                resetConnection();
                log() << "repl:  " << errmsg << endl;
                return false;
            }
        }
        return true;
    }
    
    /* note: not yet in mutex at this point.
       returns >= 0 if ok.  return -1 if you want to reconnect.
       return value of zero indicates no sleep necessary before next call
    */
    int ReplSource::sync(int& nApplied) {
        _sleepAdviceTime = 0;
        ReplInfo r("sync");
        if ( !cmdLine.quiet ) {
            Nullstream& l = log();
            l << "repl: from ";
            if( sourceName() != "main" ) {
                l << "source:" << sourceName() << ' ';
            }
            l << "host:" << hostName << endl;
        }
        nClonedThisPass = 0;

        // FIXME Handle cases where this db isn't on default port, or default port is spec'd in hostName.
        if ( (string("localhost") == hostName || string("127.0.0.1") == hostName) && cmdLine.port == CmdLine::DefaultDBPort ) {
            log() << "repl:   can't sync from self (localhost). sources configuration may be wrong." << endl;
            sleepsecs(5);
            return -1;
        }

        if ( !oplogReader.connect(hostName) ) {
			log(4) << "repl:  can't connect to sync source" << endl;
            if ( replPair && paired ) {
                assert( startsWith(hostName.c_str(), replPair->remoteHost.c_str()) );
                replPair->arbitrate();
            }
            return -1;
        }
        
        if ( paired ) {
            int remote = replPair->negotiate(oplogReader.conn(), "direct");
            int nMasters = ( remote == ReplPair::State_Master ) + ( replPair->state == ReplPair::State_Master );
            if ( getInitialSyncCompleted() && nMasters != 1 ) {
                log() << ( nMasters == 0 ? "no master" : "two masters" ) << ", deferring oplog pull" << endl;
                return 1;
            }
        }

        /*
        	// get current mtime at the server.
        	BSONObj o = conn->findOne("admin.$cmd", opTimeQuery);
        	BSONElement e = o.getField("optime");
        	if( e.eoo() ) {
        		log() << "repl:   failed to get cur optime from master" << endl;
        		log() << "        " << o.toString() << endl;
        		return false;
        	}
        	uassert( 10124 ,  e.type() == Date );
        	OpTime serverCurTime;
        	serverCurTime.asDate() = e.date();
        */
        return sync_pullOpLog(nApplied);
    }

    /* --------------------------------------------------------------*/

    /*
    TODO:
    _ source has autoptr to the cursor
    _ reuse that cursor when we can
    */

    /* returns: # of seconds to sleep before next pass 
                0 = no sleep recommended
                1 = special sentinel indicating adaptive sleep recommended
    */
    int _replMain(ReplSource::SourceVector& sources, int& nApplied) {
        {
            ReplInfo r("replMain load sources");
            dblock lk;
            ReplSource::loadAll(sources);
            replSettings.fastsync = false; // only need this param for initial reset
        }

        if ( sources.empty() ) {
            /* replication is not configured yet (for --slave) in local.sources.  Poll for config it
            every 20 seconds.
            */
            return 20;
        }

        int sleepAdvice = 1;
        for ( ReplSource::SourceVector::iterator i = sources.begin(); i != sources.end(); i++ ) {
            ReplSource *s = i->get();
            int res = -1;
            try {
                res = s->sync(nApplied);
                bool moreToSync = s->haveMoreDbsToSync();
                if( res < 0 ) { 
                    sleepAdvice = 3;
                }
                else if( moreToSync ) {
                    sleepAdvice = 0;
                }
                else if ( s->sleepAdvice() ) {
                    sleepAdvice = s->sleepAdvice();
                }
                else 
                    sleepAdvice = res;
                if ( res >= 0 && !moreToSync /*&& !s->syncedTo.isNull()*/ ) {
                    pairSync->setInitialSyncCompletedLocking();
                }
            }
            catch ( const SyncException& ) {
                log() << "caught SyncException" << endl;
                return 10;
            }
            catch ( AssertionException& e ) {
                if ( e.severe() ) {
                    log() << "replMain AssertionException " << e.what() << endl;
                    return 60;
                }
                else {
                    log() << "repl: AssertionException " << e.what() << '\n';
                }
                replInfo = "replMain caught AssertionException";
            }
            catch ( const DBException& e ) {
                log() << "repl: DBException " << e.what() << endl;
                replInfo = "replMain caught DBException";
            }
            catch ( const std::exception &e ) {
                log() << "repl: std::exception " << e.what() << endl;
                replInfo = "replMain caught std::exception";                
            }
            catch ( ... ) { 
                log() << "unexpected exception during replication.  replication will halt" << endl;
                replAllDead = "caught unexpected exception during replication";
            }
            if ( res < 0 )
                s->oplogReader.resetConnection();
        }
        return sleepAdvice;
    }

    void replMain() {
        ReplSource::SourceVector sources;
        while ( 1 ) {
            int s = 0;
            {
                dblock lk;
                if ( replAllDead ) {
                    if ( !replSettings.autoresync || !ReplSource::throttledForceResyncDead( "auto" ) )
                        break;
                }
                assert( syncing == 0 ); // i.e., there is only one sync thread running. we will want to change/fix this.
                syncing++;
            }
            try {
                int nApplied = 0;
                s = _replMain(sources, nApplied);
                if( s == 1 ) { 
                    if( nApplied == 0 ) s = 2;
                    else if( nApplied > 100 ) { 
                        // sleep very little - just enought that we aren't truly hammering master
                        sleepmillis(75);
                        s = 0;
                    }
                }
            } catch (...) {
                out() << "caught exception in _replMain" << endl;
                s = 4;
            }
            {
                dblock lk;
                assert( syncing == 1 );
                syncing--;
            }

			if( relinquishSyncingSome )  { 
				relinquishSyncingSome = 0;
				s = 1; // sleep before going back in to syncing=1
			}

            if ( s ) {
                stringstream ss;
                ss << "repl: sleep " << s << "sec before next pass";
                string msg = ss.str();
                if ( ! cmdLine.quiet )
                    log() << msg << endl;
                ReplInfo r(msg.c_str());
                sleepsecs(s);
            }
        }
    }

    int debug_stop_repl = 0;

    static void replMasterThread() {
        sleepsecs(4);
        Client::initThread("replmaster");
        int toSleep = 10;
        while( 1 ) {

            sleepsecs( toSleep );
            /* write a keep-alive like entry to the log.  this will make things like 
               printReplicationStatus() and printSlaveReplicationStatus() stay up-to-date
               even when things are idle.
            */
            {
                writelocktry lk("",1);
                if ( lk.got() ){
                    toSleep = 10;
                    
                    cc().getAuthenticationInfo()->authorize("admin");   
                        
                    try { 
                        logKeepalive();
                    }
                    catch(...) { 
                        log() << "caught exception in replMasterThread()" << endl;
                    }
                }
                else {
                    log(5) << "couldn't logKeepalive" << endl;
                    toSleep = 1;
                }
            }
        }
    }

    void replSlaveThread() {
        sleepsecs(1);
        Client::initThread("replslave");
            
        {
            dblock lk;
            cc().getAuthenticationInfo()->authorize("admin");
        
            BSONObj obj;
            if ( Helpers::getSingleton("local.pair.startup", obj) ) {
                // should be: {replacepeer:1}
                replacePeer = true;
                pairSync->setInitialSyncCompleted(); // we are the half that has all the data
            }
        }

        while ( 1 ) {
            try {
                replMain();
                if ( debug_stop_repl )
                    break;
                sleepsecs(5);
            }
            catch ( AssertionException& ) {
                ReplInfo r("Assertion in replSlaveThread(): sleeping 5 minutes before retry");
                problem() << "Assertion in replSlaveThread(): sleeping 5 minutes before retry" << endl;
                sleepsecs(300);
            }
        }
    }

    void tempThread() {
        while ( 1 ) {
            out() << dbMutex.info().isLocked() << endl;
            sleepmillis(100);
        }
    }

    void newRepl();
    void oldRepl();
    void startReplication() {
        /* if we are going to be a replica set, we aren't doing other forms of replication. */
        if( !cmdLine._replSet.empty() ) {
            if( replSettings.slave || replSettings.master || replPair ) { 
                log() << "***" << endl;
                log() << "ERROR: can't use --slave or --master replication options with --replSet" << endl;
                log() << "***" << endl;
            }
            createOplog();
            newRepl();
            return;
        }

        oldRepl();

        /* this was just to see if anything locks for longer than it should -- we need to be careful
           not to be locked when trying to connect() or query() the other side.
           */
        //boost::thread tempt(tempThread);

        if( !replSettings.slave && !replSettings.master && !replPair )
            return;

        {
            dblock lk;
            cc().getAuthenticationInfo()->authorize("admin");
            pairSync->init();
        }

        if ( replSettings.slave || replPair ) {
            if ( replSettings.slave ) {
                assert( replSettings.slave == SimpleSlave );
                log(1) << "slave=true" << endl;
            }
            else
                replSettings.slave = ReplPairSlave;
            boost::thread repl_thread(replSlaveThread);
        }

        if ( replSettings.master || replPair ) {
            if ( replSettings.master )
                log(1) << "master=true" << endl;
            replSettings.master = true;
            createOplog();
            boost::thread t(replMasterThread);
        }
        
        while( replSettings.fastsync ) // don't allow writes until we've set up from log
            sleepmillis( 50 );
    }

    /* called from main at server startup */
    void pairWith(const char *remoteEnd, const char *arb) {
        replPair = new ReplPair(remoteEnd, arb);
    }

    void testPretouch() {
        int nthr = min(8, 8);
        nthr = max(nthr, 1);
        int m = 8 / nthr;
        ThreadPool tp(nthr);
        vector<BSONObj> v;

        BSONObj x = BSON( "ns" << "test.foo" << "o" << BSON( "_id" << 1 ) << "op" << "i" );

        v.push_back(x);
        v.push_back(x);
        v.push_back(x);

        unsigned a = 0;
        while( 1 ) {
            if( a >= v.size() ) break;
            unsigned b = a + m - 1; // v[a..b]
            if( b >= v.size() ) b = v.size() - 1;
            tp.schedule(pretouchN, v, a, b);
            DEV cout << "pretouch task: " << a << ".." << b << endl;
            a += m;
        }
        tp.join();
    }
    
} // namespace mongo