Additional options

ClickHouse Connect provides a number of additional options for advanced use cases.

Global settings

There are a small number of settings that control ClickHouse Connect behavior globally. They are accessed from the top level common package:

from clickhouse_connect import common

common.set_setting('autogenerate_session_id', False)
common.get_setting('invalid_setting_action')
'drop'

Note

These common settings autogenerate_session_id, product_name, and readonly should always be modified before creating a client with the clickhouse_connect.get_client method. Changing these settings after client creation does not affect the behavior of existing clients.

The following global settings are currently defined:

Setting Name	Default	Options	Description
autogenerate_session_id	True	True, False	Autogenerate a new UUID(1) session ID (if not provided) for each client session. If no session ID is provided (either at the client or query level), ClickHouse will generate a random internal ID for each query.
dict_parameter_format	'json'	'json', 'map'	This controls whether parameterized queries convert a Python dictionary to JSON or ClickHouse Map syntax. json should be used for inserts into JSON columns, map for ClickHouse Map columns.
invalid_setting_action	'error'	'drop', 'send', 'error'	Action to take when an invalid or readonly setting is provided (either for the client session or query). If drop, the setting will be ignored, if send, the setting will be sent to ClickHouse, if error a client side ProgrammingError will be raised.
max_connection_age	600		Maximum seconds that an HTTP Keep Alive connection will be kept open/reused. This prevents bunching of connections against a single ClickHouse node behind a load balancer/proxy. Defaults to 10 minutes.
product_name			A string that is passed with the query to ClickHouse for tracking the app using ClickHouse Connect. Should be in the form <product name;&gl/<product version>.
readonly	0	0, 1	Implied "read_only" ClickHouse settings for versions prior to 19.17. Can be set to match the ClickHouse "read_only" value for settings to allow operation with very old ClickHouse versions.
send_os_user	True	True, False	Include the detected operating system user in client information sent to ClickHouse (HTTP User-Agent string).
send_integration_tags	True	True, False	Include the used integration libraries/version (e.g. Pandas/SQLAlchemy/etc.) in client information sent to ClickHouse (HTTP User-Agent string).
use_protocol_version	True	True, False	Use the client protocol version. This is needed for DateTime timezone columns but breaks with the current version of chproxy.
max_error_size	1024		Maximum number of characters that will be returned in a client error messages. Use 0 for this setting to get the full ClickHouse error message. Defaults to 1024 characters.
http_buffer_size	10MB		Size (in bytes) of the "in-memory" buffer used for HTTP streaming queries.
preserve_pandas_datetime_resolution	False	True, False	When True and using pandas 2.x, preserves the datetime64/timedelta64 dtype resolution (e.g., 's', 'ms', 'us', 'ns'). If False (or on pandas <2.x), coerces to nanosecond ('ns') resolution for compatibility.

Compression

ClickHouse Connect supports lz4, zstd, brotli, and gzip compression for both query results and inserts. Always keep in mind that using compression usually involves a tradeoff between network bandwidth/transfer speed against CPU usage (both on the client and the server.)

To receive compressed data, the ClickHouse server enable_http_compression must be set to 1, or the user must have permission to change the setting on a "per query" basis.

Compression is controlled by the compress parameter when calling the clickhouse_connect.get_client factory method. By default, compress is set to True, which will trigger the default compression settings. For queries executed with the query, query_np, and query_df client methods, ClickHouse Connect will add the Accept-Encoding header with the lz4, zstd, br (brotli, if the brotli library is installed), gzip, and deflate encodings to queries executed with the query client method (and indirectly, query_np and query_df). (For the majority of requests the ClickHouse server will return with a zstd compressed payload.) For inserts, by default ClickHouse Connect will compress insert blocks with lz4 compression, and send the Content-Encoding: lz4 HTTP header.

The get_client compress parameter can also be set to a specific compression method, one of lz4, zstd, br, or gzip. That method will then be used for both inserts and query results (if supported by the ClickHouse server.) The required zstd and lz4 compression libraries are now installed by default with ClickHouse Connect. If br/brotli is specified, the brotli library must be installed separately.

Note that the raw* client methods don't use the compression specified by the client configuration.

We also recommend against using gzip compression, as it is significantly slower than the alternatives for both compressing and decompressing data.

HTTP proxy support

ClickHouse Connect adds basic HTTP proxy support using the urllib3 library. It recognizes the standard HTTP_PROXY and HTTPS_PROXY environment variables. Note that using these environment variables will apply to any client created with the clickhouse_connect.get_client method. Alternatively, to configure per client, you can use the http_proxy or https_proxy arguments to the get_client method. For details on the implementation of HTTP Proxy support, see the urllib3 documentation.

To use a SOCKS proxy, you can send a urllib3 SOCKSProxyManager as the pool_mgr argument to get_client. Note that this will require installing the PySocks library either directly or using the [socks] option for the urllib3 dependency.

"Old" JSON data type

The experimental Object (or Object('json')) data type is deprecated and should be avoided in a production environment. ClickHouse Connect continues to provide limited support for the data type for backward compatibility. Note that this support does not include queries that are expected to return "top level" or "parent" JSON values as dictionaries or the equivalent, and such queries will result in an exception.

"New" Variant/Dynamic/JSON datatypes (experimental feature)

Beginning with the 0.8.0 release, clickhouse-connect provides experimental support for the new (also experimental) ClickHouse types Variant, Dynamic, and JSON.

Usage notes

• JSON data can be inserted as either a Python dictionary or a JSON string containing a JSON object {}. Other forms of JSON data are not supported.
• Queries using subcolumns/paths for these types will return the type of the sub column.
• See the main ClickHouse documentation for other usage notes.

Known limitations

• Each of these types must be enabled in the ClickHouse settings before using.
• The "new" JSON type is available starting with the ClickHouse 24.8 release
• Due to internal format changes, clickhouse-connect is only compatible with Variant types beginning with the ClickHouse 24.7 release
• Returned JSON objects will only return the max_dynamic_paths number of elements (which defaults to 1024). This will be fixed in a future release.
• Inserts into Dynamic columns will always be the String representation of the Python value. This will be fixed in a future release, once https://github.com/ClickHouse/ClickHouse/issues/70395 has been fixed.
• The implementation for the new types has not been optimized in C code, so performance may be somewhat slower than for simpler, established data types.