path: root/src/mongo/db/s/config/configsvr_commit_chunk_migration_command.cpp

/**
 *    Copyright (C) 2016 MongoDB 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
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#include "mongo/platform/basic.h"

#include "mongo/db/auth/authorization_session.h"
#include "mongo/db/commands.h"
#include "mongo/db/concurrency/d_concurrency.h"
#include "mongo/db/operation_context.h"
#include "mongo/db/repl/read_concern_args.h"
#include "mongo/db/s/chunk_move_write_concern_options.h"
#include "mongo/db/s/sharding_state.h"
#include "mongo/rpc/get_status_from_command_result.h"
#include "mongo/s/catalog/type_chunk.h"
#include "mongo/s/chunk_version.h"
#include "mongo/s/client/shard_registry.h"
#include "mongo/s/grid.h"
#include "mongo/s/request_types/commit_chunk_migration_request_type.h"

namespace mongo {

namespace {

/**
 * This command takes the chunk being migrated ("migratedChunk") and generates a new version for it
 * that is written along with its new shard location ("toShard") to the chunks collection. It also
 * takes a control chunk ("controlChunk") and assigns it a new version as well so that the source
 * ("fromShard") shard's shardVersion will increases. If there is no control chunk, then the chunk
 * being migrated is the source shard's only remaining chunk.
 *
 * The new chunk version is generated by querying the highest chunk version of the collection, and
 * then incrementing that major value for both migrated and control chunks and setting the minor to
 * 0 for the migrated chunk and 1 for the control chunk. A global exclusive lock is held for the
 * duration of generating the new chunk version and writing to the chunks collection so that
 * yielding cannot occur. This assures that generated ChunkVersions are strictly monotonically
 * increasing -- a second process will not be able to query for max chunk version until the first
 * finishes writing the new highest chunk version it generated.
 *
 * Command Format:
 * {
 *   _configsvrCommitChunkMigration: <database>.<collection>,
 *   migratedChunk: {min: <min_value>, max: <max_value>},
 *   controlChunk: {min: <min_value>, max: <max_value>},  (optional)
 *   fromShard: "<from_shard_name>",
 *   toShard: "<to_shard_name>",
 * }
 *
 * Returns:
 * {
 *   migratedChunkVersion: <ChunkVersion_BSON>,
 *   controlChunkVersion: <ChunkVersion_BSON>, (only present if a controlChunk is defined)
 * }
 *
 */
class ConfigSvrCommitChunkMigrationCommand : public Command {
public:
    ConfigSvrCommitChunkMigrationCommand() : Command("_configsvrCommitChunkMigration") {}

    void help(std::stringstream& help) const override {
        help << "should not be calling this directly";
    }

    bool slaveOk() const override {
        return false;
    }

    bool adminOnly() const override {
        return true;
    }

    virtual bool supportsWriteConcern(const BSONObj& cmd) const override {
        return true;
    }

    Status checkAuthForCommand(Client* client,
                               const std::string& dbname,
                               const BSONObj& cmdObj) override {
        if (!AuthorizationSession::get(client)->isAuthorizedForActionsOnResource(
                ResourcePattern::forClusterResource(), ActionType::internal)) {
            return Status(ErrorCodes::Unauthorized, "Unauthorized");
        }
        return Status::OK();
    }

    std::string parseNs(const std::string& dbname, const BSONObj& cmdObj) const override {
        return parseNsFullyQualified(dbname, cmdObj);
    }

    static void checkChunkIsOnShard(OperationContext* txn,
                                    const NamespaceString& nss,
                                    const BSONObj& min,
                                    const BSONObj& max,
                                    const ShardId& shard) {
        BSONObj chunkQuery =
            BSON(ChunkType::ns() << nss.ns() << ChunkType::min() << min << ChunkType::max() << max
                                 << ChunkType::shard()
                                 << shard);
        // Must use kLocalReadConcern because using majority will set a flag on the recovery unit
        // that conflicts with the subsequent writes in the CommitChunkMigration command.
        auto findResponse = uassertStatusOK(
            Grid::get(txn)->shardRegistry()->getConfigShard()->exhaustiveFindOnConfig(
                txn,
                ReadPreferenceSetting{ReadPreference::PrimaryOnly},
                repl::ReadConcernLevel::kLocalReadConcern,
                NamespaceString(ChunkType::ConfigNS),
                chunkQuery,
                BSONObj(),
                1));
        uassert(40165,
                str::stream()
                    << "Could not find the chunk ("
                    << chunkQuery.toString()
                    << ") on the shard. Cannot execute the migration commit with invalid chunks.",
                !findResponse.docs.empty());
    }

    BSONObj makeCommitChunkApplyOpsCommand(
        const NamespaceString& nss,
        const ChunkRange& migratedChunkRange,
        const boost::optional<ChunkRange>& controlChunkRange,
        const ChunkVersion newMigratedChunkVersion,
        const boost::optional<ChunkVersion> newControlChunkVersion,
        StringData toShard,
        StringData fromShard) {
        // Update migratedChunk's version and shard.
        BSONArrayBuilder updates;
        {
            BSONObjBuilder op;
            op.append("op", "u");
            op.appendBool("b", false);  // No upserting
            op.append("ns", ChunkType::ConfigNS);

            BSONObjBuilder n(op.subobjStart("o"));
            n.append(ChunkType::name(), ChunkType::genID(nss.ns(), migratedChunkRange.getMin()));
            newMigratedChunkVersion.addToBSON(n, ChunkType::DEPRECATED_lastmod());
            n.append(ChunkType::ns(), nss.ns());
            n.append(ChunkType::min(), migratedChunkRange.getMin());
            n.append(ChunkType::max(), migratedChunkRange.getMax());
            n.append(ChunkType::shard(), toShard);
            n.done();

            BSONObjBuilder q(op.subobjStart("o2"));
            q.append(ChunkType::name(), ChunkType::genID(nss.ns(), migratedChunkRange.getMin()));
            q.done();

            updates.append(op.obj());
        }

        // If we have a controlChunk, update its chunk version.
        if (controlChunkRange) {
            BSONObjBuilder op;
            op.append("op", "u");
            op.appendBool("b", false);
            op.append("ns", ChunkType::ConfigNS);

            BSONObjBuilder n(op.subobjStart("o"));
            n.append(ChunkType::name(), ChunkType::genID(nss.ns(), controlChunkRange->getMin()));
            newControlChunkVersion->addToBSON(n, ChunkType::DEPRECATED_lastmod());
            n.append(ChunkType::ns(), nss.ns());
            n.append(ChunkType::min(), controlChunkRange->getMin());
            n.append(ChunkType::max(), controlChunkRange->getMax());
            n.append(ChunkType::shard(), fromShard);
            n.done();

            BSONObjBuilder q(op.subobjStart("o2"));
            q.append(ChunkType::name(), ChunkType::genID(nss.ns(), controlChunkRange->getMin()));
            q.done();

            updates.append(op.obj());
        }

        // Do not give applyOps a write concern. If applyOps tries to wait for replication, it will
        // fail because of the GlobalWrite lock CommitChunkMigration already holds. Replication will
        // not be able to take the lock it requires.
        return BSON("applyOps" << updates.arr());
    }

    bool run(OperationContext* txn,
             const std::string& dbName,
             BSONObj& cmdObj,
             int options,
             std::string& errmsg,
             BSONObjBuilder& result) override {
        const NamespaceString nss = NamespaceString(parseNs(dbName, cmdObj));

        CommitChunkMigrationRequest commitChunkMigrationRequest =
            uassertStatusOK(CommitChunkMigrationRequest::createFromCommand(nss, cmdObj));

        // Run operations under a nested lock as a hack to prevent yielding. When query/applyOps
        // commands are called, they will take a second lock, and the PlanExecutor will be unable to
        // yield.
        //
        // ConfigSvrCommitChunkMigration commands must be run serially because the new ChunkVersions
        // for migrated chunks are generated within the command. Therefore it cannot be allowed to
        // yield between generating the ChunkVersion and committing it to the database with
        // applyOps.
        Lock::GlobalWrite firstGlobalWriteLock(txn->lockState());

        // Check that migratedChunk and controlChunk are where they should be, on fromShard.
        checkChunkIsOnShard(txn,
                            nss,
                            commitChunkMigrationRequest.getMigratedChunkRange().getMin(),
                            commitChunkMigrationRequest.getMigratedChunkRange().getMax(),
                            commitChunkMigrationRequest.getFromShard());

        if (commitChunkMigrationRequest.hasControlChunkRange()) {
            checkChunkIsOnShard(txn,
                                nss,
                                commitChunkMigrationRequest.getControlChunkRange().getMin(),
                                commitChunkMigrationRequest.getControlChunkRange().getMax(),
                                commitChunkMigrationRequest.getFromShard());
        }

        // Generate the new chunk version (CV). Query the current max CV of the collection. Use the
        // incremented major version of the result returned. Migrating chunk's minor version will
        // be 0, control chunk's minor version will be 1 (if control chunk is present).

        // Must use kLocalReadConcern because using majority will set a flag on the recovery unit
        // that conflicts with the subsequent writes.
        auto findResponse = uassertStatusOK(
            Grid::get(txn)->shardRegistry()->getConfigShard()->exhaustiveFindOnConfig(
                txn,
                ReadPreferenceSetting{ReadPreference::PrimaryOnly},
                repl::ReadConcernLevel::kLocalReadConcern,
                NamespaceString(ChunkType::ConfigNS),
                BSON("ns" << nss.ns()),
                BSON(ChunkType::DEPRECATED_lastmod << -1),
                1));

        std::vector<BSONObj> chunksVector = findResponse.docs;
        uassert(40164,
                str::stream() << "Tried to find max chunk version for collection '" << nss.ns()
                              << ", but found no chunks",
                !chunksVector.empty());

        ChunkVersion currentMaxVersion =
            ChunkVersion::fromBSON(chunksVector.front(), ChunkType::DEPRECATED_lastmod());

        // Generate the new versions of migratedChunk and controlChunk.
        ChunkVersion newMigratedChunkVersion =
            ChunkVersion(currentMaxVersion.majorVersion() + 1, 0, currentMaxVersion.epoch());
        boost::optional<ChunkVersion> newControlChunkVersion = boost::none;
        boost::optional<ChunkRange> newControlChunkRange = boost::none;
        if (commitChunkMigrationRequest.hasControlChunkRange()) {
            newControlChunkVersion =
                ChunkVersion(currentMaxVersion.majorVersion() + 1, 1, currentMaxVersion.epoch());
            newControlChunkRange = commitChunkMigrationRequest.getControlChunkRange();
        }

        auto applyOpsCommandResponse =
            Grid::get(txn)->shardRegistry()->getConfigShard()->runCommand(
                txn,
                ReadPreferenceSetting{ReadPreference::PrimaryOnly},
                nss.db().toString(),
                makeCommitChunkApplyOpsCommand(
                    nss,
                    commitChunkMigrationRequest.getMigratedChunkRange(),
                    newControlChunkRange,
                    newMigratedChunkVersion,
                    newControlChunkVersion,
                    commitChunkMigrationRequest.getToShard().toString(),
                    commitChunkMigrationRequest.getFromShard().toString()),
                Shard::RetryPolicy::kIdempotent);

        if (!applyOpsCommandResponse.isOK()) {
            return appendCommandStatus(result, applyOpsCommandResponse.getStatus());
        }

        if (!applyOpsCommandResponse.getValue().commandStatus.isOK()) {
            return appendCommandStatus(result, applyOpsCommandResponse.getValue().commandStatus);
        }

        newMigratedChunkVersion.appendWithFieldForCommands(&result, "migratedChunkVersion");
        if (commitChunkMigrationRequest.hasControlChunkRange()) {
            newControlChunkVersion->appendWithFieldForCommands(&result, "controlChunkVersion");
        }

        return true;
    }

} configsvrCommitChunkMigrationCommand;

}  // namespace
}  // namespace mongo