&reftitle.constants; &extension.constants;

`YAC_VERSION` (`string`)

`YAC_MAX_KEY_LEN` (`int`)

- Max length of a key could be, it is 48 bytes.

`YAC_MAX_VALUE_RAW_LEN` (`int`)

`YAC_MAX_RAW_COMPRESSED_LEN` (`int`)

`YAC_SERIALIZER_PHP` (`int`)

- Use php serialize as serializer

`YAC_SERIALIZER_JSON` (`int`)

- Use json as serializer(requrie --enable-json)

`YAC_SERIALIZER_IGBINARY` (`int`)

- Use igbinary as serializer(require --enable-igbinary)

`YAC_SERIALIZER_MSGPACK` (`int`)

- Use msgpack as serializer(require --enable-msgpack)

`YAC_SERIALIZER` (`string`)

- Which serialzier is yac used