Elasticsearch::Transport::Transport::Error: Cannot get new connection from pool.

https://sentry.gitlap.com/gitlab/gitlabcom/issues/10413/

Elasticsearch::Transport::Transport::Error: Cannot get new connection from pool.
  app/workers/elastic_indexer_worker.rb:18:in `perform'
    record.__elasticsearch__.__send__ "#{operation}_document", parent: record.es_parent
  lib/gitlab/sidekiq_middleware/request_store_middleware.rb:6:in `call'
    yield
  lib/gitlab/sidekiq_middleware/memory_killer.rb:17:in `call'
    yield
  lib/gitlab/sidekiq_middleware/arguments_logger.rb:6:in `call'
    yield
  lib/gitlab/metrics/sidekiq_middleware.rb:13:in `block in call'
    trans.run { yield }
...
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