message: use the logger's formatting
  so avoid spending any cycles on generating messages that won't print
diff: @@ -75,10 +75,12 @@ module.exports = class Indexer {
  if (filter) {
  esBody.query.bool.must.push(this._filterToES(filter));
  }
  + this.log.debug('search %j', esBody);
  let result = await this.es.search({
  index: branch,
  body: esBody
  });
  + this.log.debug('searchResult %j', result);
  return result.hits.hits.map(entry => ({ type: entry._type, id: entry._id, document: entry._source}));
  }
  @@ -148,10 +150,10 @@ module.exports = class Indexer {
  let haveMapping = await this._esMapping(branch);
  let wantMapping = await this._gitMapping(tree);
  if (this._stableMapping(haveMapping, wantMapping)) {
  - this.log.info(`${branch}: mapping already OK`);
  + this.log.info('%s: mapping already OK', branch);
  } else {
  - this.log.info(`${branch}: mapping needs update`);
  - this.log.debug(JSON.stringify({ haveMapping, wantMapping }, null, 2));
  + this.log.info('%s: mapping needs update', branch);
  + this.log.debug('%j', { haveMapping, wantMapping });
  let tmpIndex = this._tempIndexName(branch);
  await this.es.indices.create({
  index: tmpIndex,
  @@ -243,9 +245,9 @@ module.exports = class Indexer {
  async _reindex(newIndex, branch) {
  let alias = await this.es.indices.getAlias({ name: branch, ignore: [404] });
  if (alias.status === 404) {
  - this.log.info(`${branch} is new, nothing to reindex`);
  + this.log.info('%s is new, nothing to reindex', branch);
  } else {
  - this.log.info(`reindexing ${branch}`);
  + this.log.info('reindexing %s', branch);
  await this.es.reindex({
  body: {
  source: { index: branch },
  