What does it mean when MySQL is in the state Sending data

Question

What does it mean if the Mysql query   SHOW PROCESSLIST    returns  Sending data  in the State column     I imagine it means the query has been executed and MySQL is sending    result    Data to the client but I m wondering why its taking so much time  up to an hour    Thank you

User · Answer

In this state      The thread is reading and processing rows for a   SELECT statement  and sending data to the client        Because operations occurring during this this state tend to perform   large amounts of disk access  reads     That s why it takes more time to complete and so is the longest-running state over the lifetime of a given query

User · Answer

This is quite a misleading status  It should be called  reading and filtering data    This means that MySQL has some data stored on the disk  or in memory  which is yet to be read and sent over  It may be the table itself  an index  a temporary table  a sorted output etc   If you have a 1M records table  without an index  of which you need only one record  MySQL will still output the status as  sending data  while scanning the table  despite the fact it has not sent anything yet

[mysql] What does it mean when MySQL is in the state "Sending data"?

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