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# HOW REPLICATION WORKS

IO_THREAD connects to a master, reads binary log events from the master as they come in and just copies them over to a local log file called relay log. 
SQL_THREAD reads events from a relay log stored locally on the replication slave and then applies them as fast as possible. 

There could be two reasons for delay in replication: 
1. IO_THREAD delay
2. SQL_THREAD deplay

# HOW TO INDENTIFY REPLICATION LAG

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-- 
-- To create the group 
-- 

-- Create a ro_group (readonly group)
CREATE ROLE ro_group;

-- Grant access to existing tables
GRANT USAGE ON SCHEMA public TO ro_group;