path: root/src/mongo/s/d_merge.cpp

/**
 *    Copyright (C) 2013 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/>.
 *
 *    As a special exception, the copyright holders give permission to link the
 *    code of portions of this program with the OpenSSL library under certain
 *    conditions as described in each individual source file and distribute
 *    linked combinations including the program with the OpenSSL library. You
 *    must comply with the GNU Affero General Public License in all respects
 *    for all of the code used other than as permitted herein. If you modify
 *    file(s) with this exception, you may extend this exception to your
 *    version of the file(s), but you are not obligated to do so. If you do not
 *    wish to do so, delete this exception statement from your version. If you
 *    delete this exception statement from all source files in the program,
 *    then also delete it in the license file.
 */

#define MONGO_LOG_DEFAULT_COMPONENT ::mongo::logger::LogComponent::kSharding

#include "mongo/platform/basic.h"

#include <vector>

#include "mongo/client/connpool.h"
#include "mongo/db/concurrency/d_concurrency.h"
#include "mongo/db/namespace_string.h"
#include "mongo/db/operation_context.h"
#include "mongo/s/catalog/catalog_manager.h"
#include "mongo/s/chunk.h"
#include "mongo/s/config.h"
#include "mongo/s/d_state.h"
#include "mongo/s/catalog/dist_lock_manager.h"
#include "mongo/s/grid.h"
#include "mongo/util/log.h"
#include "mongo/util/mongoutils/str.h"

namespace mongo {

    using std::endl;
    using std::string;
    using mongoutils::str::stream;

    static Status runApplyOpsCmd(const std::vector<ChunkType>&,
                                 const ChunkVersion&,
                                 const ChunkVersion&);

    static BSONObj buildMergeLogEntry(const std::vector<ChunkType>&,
                                      const ChunkVersion&,
                                      const ChunkVersion&);

    static bool isEmptyChunk( const ChunkType& );

    bool mergeChunks( OperationContext* txn,
                      const NamespaceString& nss,
                      const BSONObj& minKey,
                      const BSONObj& maxKey,
                      const OID& epoch,
                      string* errMsg ) {

        //
        // Get sharding state up-to-date
        //

        ConnectionString configLoc = ConnectionString::parse( shardingState.getConfigServer(),
                                                              *errMsg );
        if ( !configLoc.isValid() ){
            warning() << *errMsg << endl;
            return false;
        }

        //
        // Get the distributed lock
        //

        string whyMessage = stream() << "merging chunks in " << nss.ns()
                                     << " from " << minKey << " to " << maxKey;
        auto scopedDistLock = grid.catalogManager()->getDistLockManager()->lock(
                nss.ns(), whyMessage);

        if (!scopedDistLock.isOK()) {
            *errMsg = stream() << "could not acquire collection lock for " << nss.ns()
                               << " to merge chunks in [" << minKey << "," << maxKey << ")"
                               << causedBy(scopedDistLock.getStatus());

            warning() << *errMsg << endl;
            return false;
        }

        //
        // We now have the collection lock, refresh metadata to latest version and sanity check
        //

        ChunkVersion shardVersion;
        Status status = shardingState.refreshMetadataNow(txn, nss.ns(), &shardVersion);

        if ( !status.isOK() ) {

            *errMsg = str::stream() << "could not merge chunks, failed to refresh metadata for "
                                    << nss.ns() << causedBy( status.reason() );

            warning() << *errMsg << endl;
            return false;
        }

        if ( epoch.isSet() && shardVersion.epoch() != epoch ) {

            *errMsg = stream() << "could not merge chunks, collection " << nss.ns()
                               << " has changed" << " since merge was sent" << "(sent epoch : "
                               << epoch.toString()
                               << ", current epoch : " << shardVersion.epoch().toString() << ")";

            warning() << *errMsg << endl;
            return false;
        }

        CollectionMetadataPtr metadata = shardingState.getCollectionMetadata( nss.ns() );

        if ( !metadata || metadata->getKeyPattern().isEmpty() ) {

            *errMsg = stream() << "could not merge chunks, collection " << nss.ns()
                               << " is not sharded";

            warning() << *errMsg << endl;
            return false;
        }

        dassert( metadata->getShardVersion().equals( shardVersion ) );

        if ( !metadata->isValidKey( minKey ) || !metadata->isValidKey( maxKey ) ) {

            *errMsg = stream() << "could not merge chunks, the range "
                               << rangeToString( minKey, maxKey ) << " is not valid"
                               << " for collection " << nss.ns() << " with key pattern "
                               << metadata->getKeyPattern();

            warning() << *errMsg << endl;
            return false;
        }

        //
        // Get merged chunk information
        //

        ChunkVersion mergeVersion = metadata->getCollVersion();
        mergeVersion.incMinor();

        std::vector<ChunkType> chunksToMerge;

        ChunkType itChunk;
        itChunk.setMin( minKey );
        itChunk.setMax( minKey );
        itChunk.setNS( nss.ns() );
        itChunk.setShard( shardingState.getShardName() );

        while (itChunk.getMax().woCompare(maxKey) < 0 &&
                metadata->getNextChunk(itChunk.getMax(), &itChunk)) {
            chunksToMerge.push_back(itChunk);
        }

        if ( chunksToMerge.empty() ) {

            *errMsg = stream() << "could not merge chunks, collection " << nss.ns()
                               << " range starting at " << minKey
                               << " and ending at " << maxKey
                               << " does not belong to shard " << shardingState.getShardName();

            warning() << *errMsg << endl;
            return false;
        }

        //
        // Validate the range starts and ends at chunks and has no holes, error if not valid
        //

        BSONObj firstDocMin = chunksToMerge.front().getMin();
        BSONObj firstDocMax = chunksToMerge.front().getMax();
        // minKey is inclusive
        bool minKeyInRange = rangeContains( firstDocMin, firstDocMax, minKey );

        if ( !minKeyInRange ) {

            *errMsg = stream() << "could not merge chunks, collection " << nss.ns()
                               << " range starting at " << minKey
                               << " does not belong to shard " << shardingState.getShardName();

            warning() << *errMsg << endl;
            return false;
        }

        BSONObj lastDocMin = chunksToMerge.back().getMin();
        BSONObj lastDocMax = chunksToMerge.back().getMax();
        // maxKey is exclusive
        bool maxKeyInRange = lastDocMin.woCompare( maxKey ) < 0 &&
                lastDocMax.woCompare( maxKey ) >= 0;

        if ( !maxKeyInRange ) {
            *errMsg = stream() << "could not merge chunks, collection " << nss.ns()
                               << " range ending at " << maxKey
                               << " does not belong to shard " << shardingState.getShardName();

            warning() << *errMsg << endl;
            return false;
        }

        bool validRangeStartKey = firstDocMin.woCompare( minKey ) == 0;
        bool validRangeEndKey = lastDocMax.woCompare( maxKey ) == 0;

        if ( !validRangeStartKey || !validRangeEndKey ) {

            *errMsg = stream() << "could not merge chunks, collection " << nss.ns()
                               << " does not contain a chunk "
                               << ( !validRangeStartKey ? "starting at " + minKey.toString() : "" )
                               << ( !validRangeStartKey && !validRangeEndKey ? " or " : "" )
                               << ( !validRangeEndKey ? "ending at " + maxKey.toString() : "" );

            warning() << *errMsg << endl;
            return false;
        }

        if ( chunksToMerge.size() == 1 ) {

            *errMsg = stream() << "could not merge chunks, collection " << nss.ns()
                               << " already contains chunk for " << rangeToString( minKey, maxKey );

            warning() << *errMsg << endl;
            return false;
        }

        // Look for hole in range
        for (size_t i = 1; i < chunksToMerge.size(); ++i) {
            if (chunksToMerge[i-1].getMax().woCompare(chunksToMerge[i].getMin()) != 0) {
                *errMsg = stream() << "could not merge chunks, collection " << nss.ns()
                                   << " has a hole in the range " << rangeToString(minKey, maxKey)
                                   << " at " << rangeToString(chunksToMerge[i-1].getMax(),
                                                              chunksToMerge[i].getMin());

                warning() << *errMsg << endl;
                return false;
            }
        }

        //
        // Run apply ops command
        //
        Status applyOpsStatus = runApplyOpsCmd(chunksToMerge, shardVersion, mergeVersion);
        if (!applyOpsStatus.isOK()) {
            warning() << applyOpsStatus;
            return false;
        }

        //
        // Install merged chunk metadata
        //

        {
            ScopedTransaction transaction(txn, MODE_IX);
            Lock::DBLock writeLk(txn->lockState(), nss.db(), MODE_IX);
            Lock::CollectionLock collLock(txn->lockState(), nss.ns(), MODE_X);
            shardingState.mergeChunks(txn, nss.ns(), minKey, maxKey, mergeVersion);
        }

        //
        // Log change
        //

        BSONObj mergeLogEntry = buildMergeLogEntry( chunksToMerge,
                                                    shardVersion,
                                                    mergeVersion );

        grid.catalogManager()->logChange(txn, "merge", nss.ns(), mergeLogEntry);

        return true;
    }

    //
    // Utilities for building BSONObjs for applyOps and change logging
    //

    BSONObj buildMergeLogEntry(const std::vector<ChunkType>& chunksToMerge,
                               const ChunkVersion& currShardVersion,
                               const ChunkVersion& newMergedVersion) {

        BSONObjBuilder logDetailB;

        BSONArrayBuilder mergedB( logDetailB.subarrayStart( "merged" ) );

        for (const ChunkType& chunkToMerge : chunksToMerge) {
            mergedB.append(chunkToMerge.toBSON());
        }

        mergedB.done();

        currShardVersion.addToBSON( logDetailB, "prevShardVersion" );
        newMergedVersion.addToBSON( logDetailB, "mergedVersion" );

        return logDetailB.obj();
    }


    BSONObj buildOpMergeChunk( const ChunkType& mergedChunk ) {

        BSONObjBuilder opB;

        // Op basics
        opB.append( "op" , "u" );
        opB.appendBool( "b" , false ); // no upserting
        opB.append( "ns" , ChunkType::ConfigNS );

        // New object
        opB.append( "o", mergedChunk.toBSON() );

        // Query object
        opB.append( "o2",
                    BSON( ChunkType::name( mergedChunk.getName() ) ) );

        return opB.obj();
    }

    BSONObj buildOpRemoveChunk( const ChunkType& chunkToRemove ) {

        BSONObjBuilder opB;

        // Op basics
        opB.append( "op", "d" ); // delete
        opB.append( "ns", ChunkType::ConfigNS );

        opB.append( "o", BSON( ChunkType::name( chunkToRemove.getName() ) ) );

        return opB.obj();
    }

    BSONArray buildOpPrecond(const string& ns,
                             const string& shardName,
                             const ChunkVersion& shardVersion) {
        BSONArrayBuilder preCond;
        BSONObjBuilder condB;
        condB.append( "ns", ChunkType::ConfigNS );
        condB.append( "q", BSON( "query" << BSON( ChunkType::ns( ns ) )
                              << "orderby" << BSON( ChunkType::DEPRECATED_lastmod() << -1 ) ) );
        {
            BSONObjBuilder resB( condB.subobjStart( "res" ) );
            shardVersion.addToBSON( resB, ChunkType::DEPRECATED_lastmod() );
            resB.done();
        }
        preCond.append(condB.obj());
        return preCond.arr();
    }

    Status runApplyOpsCmd(const std::vector<ChunkType>& chunksToMerge,
                          const ChunkVersion& currShardVersion,
                          const ChunkVersion& newMergedVersion) {

        BSONArrayBuilder updatesB;

        // The chunk we'll be "expanding" is the first chunk
        const ChunkType& firstChunk = chunksToMerge.front();

        // Fill in details not tracked by metadata
        ChunkType mergedChunk(firstChunk);
        mergedChunk.setName(Chunk::genID(firstChunk.getNS(), firstChunk.getMin()));
        mergedChunk.setMax(chunksToMerge.back().getMax());
        mergedChunk.setVersion(newMergedVersion);

        updatesB.append(buildOpMergeChunk(mergedChunk));

        // Don't remove chunk we're expanding
        for (size_t i = 1; i < chunksToMerge.size(); ++i) {
            ChunkType chunkToMerge(chunksToMerge[i]);
            chunkToMerge.setName(Chunk::genID(chunkToMerge.getNS(), chunkToMerge.getMin()));
            updatesB.append(buildOpRemoveChunk(chunkToMerge));
        }

        BSONArray preCond = buildOpPrecond(firstChunk.getNS(),
                                           firstChunk.getShard(),
                                           currShardVersion);
        return grid.catalogManager()->applyChunkOpsDeprecated(updatesB.arr(), preCond);
    }

}