void DocumentSourceOutReplaceColl::initializeWriteNs() {
    DBClientBase* conn = pExpCtx->mongoProcessInterface->directClient();

    const auto& outputNs = getOutputNs();
    _tempNs = NamespaceString(str::stream() << outputNs.db() << ".tmp.agg_out."
                                            << aggOutCounter.addAndFetch(1));

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

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

    if (_originalIndexes.empty()) {
        return;
    }

    // Copy the indexes of the output collection to the temp collection.
    std::vector<BSONObj> tempNsIndexes;
    for (const auto& indexSpec : _originalIndexes) {
        // Replace the spec's 'ns' field value, which is the original collection, with the temp
        // collection.
        tempNsIndexes.push_back(indexSpec.addField(BSON("ns" << _tempNs.ns()).firstElement()));
    }
    try {
        conn->createIndexes(_tempNs.ns(), tempNsIndexes);
    } catch (DBException& ex) {
        ex.addContext("Copying indexes for $out failed");
        throw;
    }
};