Clickhouse: LowCardinality wire and read protocol

[vahid-sohrabloo]

I'm writing Golang driver for Clickhouse. I really confused about reading and writing LowCardinality columns. I try to read source code but...
Can you explain how to reading and writing LowCardinality columns?

[KochetovNicolai]

If you just need to easily support LowCardinality(T), you may set setting low_cardinality_allow_in_native_format=0 for client session and work with data the same way as if it has type T. Server will automatically convert LowCardinality(T) -> T for selects and T -> LowCardinality(T) for inserts if needed.

If you want fully support LowCardinality(T), this is a good example (python, but code is pretty readable): https://github.com/mymarilyn/clickhouse-driver/blob/a6af47922826294a9173659c599a434c1e77803b/clickhouse_driver/columns/lowcardinalitycolumn.py

Technically, format is following:

Version UInt64
dictionary_size UInt64
Dictionary
indices_size UInt64
Indices

Version also contains the type of indices. version & 0xf is a number 0, 1, 2 or 3 for UInt8, UInt16, UInt32, UInt64 respectively.
Dictionary is a serialized column of type T.
If nested type is Nullable(T), we use type T for dictionary, and assume that 0th element contains Null.
Next element of dictionary (1st for Nullable, 0th for usual type) contains type default (zero or empty string).
Indices is a numeric column of type taken from version, which contains indices_size elements.

[vahid-sohrabloo]

Thanks @KochetovNicolai. you saved my day