======= Queries

This page presents problems encountered with queries in Presto.

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Request Header Fields Too Large

Problem ^^^^^^^

A query may return an error similar to the following example:

.. code-block:: none

Error running command: Error starting query at http://localhost:8080/v1/statement 
returned an invalid response: JsonResponse{statusCode=431, statusMessage=Request 
Header Fields Too Large, headers={connection=[close], content-length=[74], 
content-type=[text/html;charset=iso-8859-1]}, hasValue=false} 
[Error: <h1>Bad Message 431</h1><pre>reason: Request Header Fields Too Large</pre>]

Some examples of how this can happen are:

• many session properties have been added to the query
• putting a lot of information in clientInfo
• large security keys being sent in the session

If such an error happens, increasing the value of http-server.max-request-header-size
can help avoid it.

Solution ^^^^^^^^

Edit config.properties for the Presto coordinator, and set the value of the http-server.max-request-header-size configuration property to a larger size. For example:

.. code-block:: none

http-server.max-request-header-size=5MB

See :ref:admin/properties:\`http-server.max-request-header-size```.

Alternatively, avoid using prepared statements for large queries. Prepared statements place the SQL template in request headers, which can exceed the header size limit.