mongodb源码分析(十一)数据的删除

        本文我们将删除,删除操作概括起来就是遍历将collection中数据对应的索引删除,然后是删除数据,最后将删除

的空间加入到之前文章描述的deletelist中.下面我们来看具体的代码吧.删除的入口是receiveDelete函数.

    void receivedDelete(Message& m, CurOp& op) {        DbMessage d(m);        const char *ns = d.getns();        op.debug().ns = ns;        int flags = d.pullInt();        bool justOne = flags & RemoveOption_JustOne;//值删除单条doc        bool broadcast = flags & RemoveOption_Broadcast;        verify( d.moreJSObjs() );        BSONObj pattern = d.nextJsObj();        op.debug().query = pattern;        op.setQuery(pattern);        PageFaultRetryableSection s;        while ( 1 ) {            try {                Lock::DBWrite lk(ns);                // writelock is used to synchronize stepdowns w/ writes                uassert( 10056 ,  "not master", isMasterNs( ns ) );                // if this ever moves to outside of lock, need to adjust check Client::Context::_finishInit                if ( ! broadcast && handlePossibleShardedMessage( m , 0 ) )                    return;                Client::Context ctx(ns);//具体的删除函数                long long n = deleteObjects(ns, pattern, justOne, true);                lastError.getSafe()->recordDelete( n );                break;            }            catch ( PageFaultException& e ) {                LOG(2) << "recordDelete got a PageFaultException" << endl;                e.touch();            }        }    }

receiveDelete->deleteObjects

    long long deleteObjects(const char *ns, BSONObj pattern, bool justOne, bool logop, bool god, RemoveSaver * rs ) {        long long nDeleted = 0;//根据查询条件得到游标        shared_ptr< Cursor > creal = NamespaceDetailsTransient::getCursor( ns, pattern );        if( !creal->ok() )            return nDeleted;        shared_ptr< Cursor > cPtr = creal;        auto_ptr<ClientCursor> cc( new ClientCursor( QueryOption_NoCursorTimeout, cPtr, ns) );        cc->setDoingDeletes( true );        CursorId id = cc->cursorid();        bool canYield = !god && !(creal->matcher() && creal->matcher()->docMatcher().atomic());        do {            // TODO: we can generalize this I believe            //                   bool willNeedRecord = (creal->matcher() && creal->matcher()->needRecord()) || pattern.isEmpty() || isSimpleIdQuery( pattern );            if ( ! willNeedRecord ) {                // TODO: this is a total hack right now                // check if the index full encompasses query                if ( pattern.nFields() == 1 &&                      str::equals( pattern.firstElement().fieldName() , creal->indexKeyPattern().firstElement().fieldName() ) )                    willNeedRecord = true;            }            if ( canYield && ! cc->yieldSometimes( willNeedRecord ? ClientCursor::WillNeed : ClientCursor::MaybeCovered ) ) {                cc.release(); // has already been deleted elsewhere                // TODO should we assert or something?                break;            }            if ( !cc->ok() ) {                break; // if we yielded, could have hit the end            }            // this way we can avoid calling prepareToYield() every time (expensive)            // as well as some other nuances handled            cc->setDoingDeletes( true );            DiskLoc rloc = cc->currLoc();            BSONObj key = cc->currKey();            bool match = creal->currentMatches();            cc->advance();            if ( ! match )                continue;            // SERVER-5198 Advance past the document to be modified, but see SERVER-5725.            while( cc->ok() && rloc == cc->currLoc() ) {//多值索引就会出现这种状况,需要跳过同一条记录                cc->advance();            }            bool foundAllResults = ( justOne || !cc->ok() );            if ( !foundAllResults ) {                // NOTE: Saving and restoring a btree cursor's position was historically described                // as slow here.                cc->c()->prepareToTouchEarlierIterate();            }            if ( logop ) {//记录删除动作                BSONElement e;                if( BSONObj::make( rloc.rec() ).getObjectID( e ) ) {                    BSONObjBuilder b;                    b.append( e );                    bool replJustOne = true;                    logOp( "d", ns, b.done(), 0, &replJustOne );                }                else {                    problem() << "deleted object without id, not logging" << endl;                }            }            if ( rs )//将要删除的doc记录下来                rs->goingToDelete( rloc.obj() /*cc->c->current()*/ );            theDataFileMgr.deleteRecord(ns, rloc.rec(), rloc);//记录的删除            nDeleted++;            if ( foundAllResults ) {                break;            }            cc->c()->recoverFromTouchingEarlierIterate();            if( !god )                 getDur().commitIfNeeded();            if( debug && god && nDeleted == 100 )                 log() << "warning high number of deletes with god=true which could use significant memory" << endl;        }        while ( cc->ok() );        if ( cc.get() && ClientCursor::find( id , false ) == 0 ) {            // TODO: remove this and the id declaration above if this doesn't trigger            //       if it does, then i'm very confused (ERH 06/2011)            error() << "this should be impossible" << endl;            printStackTrace();            cc.release();        }        return nDeleted;    }

receiveDelete->deleteObjects->deleteRecord

    void DataFileMgr::deleteRecord(const char *ns, Record *todelete, const DiskLoc& dl, bool cappedOK, bool noWarn, bool doLog ) {        NamespaceDetails* d = nsdetails(ns);        if ( d->isCapped() && !cappedOK ) {            out() << "failing remove on a capped ns " << ns << endl;            uassert( 10089 ,  "can't remove from a capped collection" , 0 );            return;        }        BSONObj toDelete;        if ( doLog ) {            BSONElement e = dl.obj()["_id"];            if ( e.type() ) {                toDelete = e.wrap();            }        }        /* check if any cursors point to us.  if so, advance them. */        ClientCursor::aboutToDelete(dl);        unindexRecord(d, todelete, dl, noWarn);//删除索引,循环删除所有索引中记录todelete的部分.        _deleteRecord(d, ns, todelete, dl);//实际的数据删除并将其空间添加到deletedList中        NamespaceDetailsTransient::get( ns ).notifyOfWriteOp();        if ( ! toDelete.isEmpty() ) {            logOp( "d" , ns , toDelete );        }    }

         到这里删除过程结束,可见这部分流程是很简单的.

原文链接: mongodb源码分析(十一)数据的删除

作者: yhjj0108,杨浩