Problems with mysql indexing

problem description

take over a new database, today found table data 50G, and then various indexes 75G, of which three large indexes are each around 23g, and most of the large indexes are bound to timestamps.

what result do you expect? What is the error message actually seen?

so now you need to optimize this table. How can I reduce the index size? In general, how to solve this kind of problem, and what are the steps

MySQL Query : SELECT * FROM `codeshelper`.`v9_news` WHERE status=99 AND catid='6' ORDER BY rand() LIMIT 5
MySQL Error : Disk full (/tmp/#sql-temptable-64f5-1b355c5-34339.MAI); waiting for someone to free some space... (errno: 28 "No space left on device")
MySQL Errno : 1021
Message : Disk full (/tmp/#sql-temptable-64f5-1b355c5-34339.MAI); waiting for someone to free some space... (errno: 28 "No space left on device")
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