How to get full query text from performance_schema.threads? According to documentation:
Access to the threads table does not require a mutex 
and has minimal impact on server  performance. The other
sources have negative performance consequences because they require a mutex. 

So yes, I want to use threads table to examine running queries. The trouble is, the PROCESSLIST_INFO column does not contain the full query. It just contains a truncated version of the query. There is a flag viz performance_schema_max_sql_text_length which controls how many bytes are allocated for the SQL query. But it seems to affect the events_statements_history_long table. There is no change in the thread table output. Am I missing something?
As I read the manual, ... (In other words, I did not test the following.)
It cannot be set dynamically; the manual is clear on that.  Instead, you should be able to set performance_schema_max_sql_text_length in the config file (my.cnf, etc).  That would require a restart of the server.
Note: The setting is limited to 1MB.