pt-config-diff: MySQL truncates run-time variable values longer than 1024 characters

[dbnski]

pt-config-diff relies on SHOW GLOBAL VARIABLES for listing run-time variables. MySQL 5.7 and newer implement the command by reading the contents of the performance_schema table called global_variables, but the table definition uses VARCHAR(1024) for the value field. Any value longer than 1024 characters becomes truncated both in the table as well as in the SHOW GLOBAL VARIABLES command output. This makes comparing long run-time variables unreliable. The patch works around the problem by reading full values from the @@global object whenever necessary.

[it-percona-cla]

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