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DB schema change from varchar(64) to 255 takes 4 yrs and counting
WP transients being cut off because column is too short (64 characters). Considering you can add underscores and make sure transient unique and self explanatory when searching for it to debug - it's very easy to reach the limit... And extending varchar doesn't need that much of the debugging anyway prior to deployment. Good job Wordpress.
https://core.trac.wordpress.org/ticket/13310