Noticed in my Postgres log that inserts into the user_preference table have been failing. Here is the log entry:

ERROR: value too long for type character varying(255)
STATEMENT: UPDATE mdl_user_preferences SET value = 'a:2:{s:14:\"aggregatesonly\";a:11:

s:10:\"gradesonly\";a:2:{i:1;s:4:\"1620\";i:2;s:4:\"3024\";}}' WHERE id =
'1619';

A quick look at the DB for the record in question:

select * from mdl_user_preferences where id = '1619';
id | userid | name | value
---------------------------------------------------+-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
1619 | 12405 | grade_report_grader_collapsed_categories | a:2:{s:14:"aggregatesonly";a:11:

s:10:"gradesonly";a:1:{i:1;s:4:"1620";}}

Unfortunately, I cannot determine how exactly this was triggered. I
cannot decipher exactly what was being clicked on by the user at the
time these things were logged. Any tips on recreating the problem?

If I were to guess, I would say that there is a problem where a
person may belong to too many courses with too many categories and
have PHP pref arrays that don't serialize to a small enough value.
Perhaps the size of the serialized value should be checked or else a
note presented to the user to that the settings were not saved?