Exemplo n.º 1
0
void DocumentSourceOut::initialize() {
    DBClientBase* conn = pExpCtx->mongoProcessInterface->directClient();

    // Save the original collection options and index specs so we can check they didn't change
    // during computation.
    _originalOutOptions = pExpCtx->mongoProcessInterface->getCollectionOptions(_outputNs);
    _originalIndexes = conn->getIndexSpecs(_outputNs.ns());

    // Check if it's sharded or capped to make sure we have a chance of succeeding before we do all
    // the work. If the collection becomes capped during processing, the collection options will
    // have changed, and the $out will fail. If it becomes sharded during processing, the final
    // rename will fail.
    uassert(17017,
            str::stream() << "namespace '" << _outputNs.ns()
                          << "' is sharded so it can't be used for $out'",
            !pExpCtx->mongoProcessInterface->isSharded(pExpCtx->opCtx, _outputNs));
    uassert(17152,
            str::stream() << "namespace '" << _outputNs.ns()
                          << "' is capped so it can't be used for $out",
            _originalOutOptions["capped"].eoo());

    // We will write all results into a temporary collection, then rename the temporary collection
    // to be the target collection once we are done.
    _tempNs = NamespaceString(str::stream() << _outputNs.db() << ".tmp.agg_out."
                                            << aggOutCounter.addAndFetch(1));

    // Create output collection, copying options from existing collection if any.
    {
        BSONObjBuilder cmd;
        cmd << "create" << _tempNs.coll();
        cmd << "temp" << true;
        cmd.appendElementsUnique(_originalOutOptions);

        BSONObj info;
        bool ok = conn->runCommand(_outputNs.db().toString(), cmd.done(), info);
        uassert(16994,
                str::stream() << "failed to create temporary $out collection '" << _tempNs.ns()
                              << "': "
                              << info.toString(),
                ok);
    }

    // copy indexes to _tempNs
    for (std::list<BSONObj>::const_iterator it = _originalIndexes.begin();
         it != _originalIndexes.end();
         ++it) {
        MutableDocument index((Document(*it)));
        index.remove("_id");  // indexes shouldn't have _ids but some existing ones do
        index["ns"] = Value(_tempNs.ns());

        BSONObj indexBson = index.freeze().toBson();
        conn->insert(_tempNs.getSystemIndexesCollection(), indexBson);
        BSONObj err = conn->getLastErrorDetailed();
        uassert(16995,
                str::stream() << "copying index for $out failed."
                              << " index: "
                              << indexBson
                              << " error: "
                              << err,
                DBClientBase::getLastErrorString(err).empty());
    }
    _initialized = true;
}