Motivation:

• logs will be stored in structured format for easy and efficient searching, visualization and analytics, even in distributed clusters;
• allow to store data for larger periods of time due to better compression and usability;
• the user will be able to fine tune TTL in ClickHouse and to store old text logs in files for shorter time;
• allow to store more fields in structured log.

Downsides:

• logs in system tables are available only if clickhouse-server is alive; but it's Ok, because text logs in files will be available nevertheless.

Look for SystemLog.h and QueryLog, QueryThreadLog, PartLog for implementation. Proposed name: TextLog, system.text_log.

Fields (already existing in text log):

• event_date Date;
• event_time DateTime;
• microseconds UInt32;
• thread_number UInt32;
• query_id String;
• level Enum;
• logger_name String;
• message String;

Fields (extra):

• os_thread_id UInt32;
• thread_name LowCardinality(String);
• server version and revision fields similar to query_log;
• source_file LowCardinality(String); - information about source file location;
• source_line UInt64;