Use case
Remove long base64 and hex encoded paramters that look random. Example:

http://yandex.ru/clck/jsredir?from=yandex.ru;search%2F;web;;&text=&etext=1004&cst=AiuY0DBWFJ5Hyx_fyvalFPA3abBqdnSOApSiLPWwVkIeiz46AroRCQXrfJ8M5oYTWorWEWccK4Kw_QEhSDD6X4nGMT4OabEk0xnry4NtnOEzWFPU4iTzunSVVjkuY7CYolnD7hb04cMRv7iMnaO8LjNm0hxqvwN9sXCzUYeXp_muLsdY4W99_U5MJKGmz7IAmR5-ceoAoaBB2XGYAS9BTYKbbvlmneBpbf_SwAd_6OOACXtLmRXqXad3AQbcArYE8LCO0zmE9vpha3yoT0jl8pd9CUmbGZR5nA3sf5TcDFTpr5nYaOdxjmHep2cZeW3QHvPtKA2xWXW6qzGrQeZ1SEOPcJ1afJqmAHisup90hhNYyl2hxl8xn_DtCRbJqYHb88JtuQ3591EGW42wPZhSbxBFdU0KIZN3c_VZOmk6avzKzqG_kJpjPObWXbh9qs0S23WxDGCcPUrIzi3ESSLv1qgaRhqkfjBc57BFVA4RxlljpKQdeVeTbklJgqptznf1aHZQ2wYARBzC_jvv994MCTZIus_NctCMWoSaU74OaMmo0h5ScYLI2CWy6nj5PbhCrgeLsaEBVOQT9xoLSoCRfJ78xI_T1ruuD3QBJmHY6YW8f5UM36LRbzhd5vmNTPRvrs2wcCFhF_w&l10n=ru&cts=1458904227333&mc=1.584962500721156

Note: these parameters are usually not "garbage" but they are impossible to decrypt and they will waste space on disk. We are already removing these parameters from Yandex, Google, etc. before inserting into ClickHouse.

Implementation
For parameters of some minimal length, quickly calculate some statistics like:

• does not contain symbols that are not in base64 or base64-for-URL;
• distribution looks uniform.