Elasticsearch-PHP uses an interchangeable HTTP transport layer called RingPHP. This allows the client to construct a generic HTTP request, then pass it to the transport layer to execute. The actual execution details are hidden from the client and it is modular, so that you can choose from several HTTP handlers depending on your needs.

The default handler that the client uses is a combination handler. When executing in synchronous mode, the handler uses CurlHandler, which executes single curl calls. These are very fast for single requests. When asynchronous (future) mode is enabled, the handler switches to CurlMultiHandler, which uses the curl_multi interface. This involves a bit more overhead, but allows batches of HTTP requests to be processed in parallel.

You can configure the HTTP handler with one of several helper functions, or provide your own custom handler:

$defaultHandler = ClientBuilder::defaultHandler();
$singleHandler  = ClientBuilder::singleHandler();
$multiHandler   = ClientBuilder::multiHandler();
$customHandler  = new MyCustomHandler();

$client = ClientBuilder::create()
            ->setHandler($defaultHandler)
            ->build();

For details on creating your own custom Ring handler, please see the RingPHP Documentation

The default handler is recommended in almost all cases. This allows fast synchronous execution, while retaining flexibility to invoke parallel batches with async future mode. You may consider using just the singleHandler if you know you will never need async capabilities, since it will save a small amount of overhead by reducing indirection.