Problem:
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- When online alter of InnoDB statistics table happens,
any transaction which updates the statistics table
has to read the undo log and log the DML changes during
transaction commit. Applying undo log
(UndorecApplier::apply_undo_rec) requires a shared
lock on dictionary cache but dict_stats_save() already
holds write lock on dictionary cache. This leads to
abort of server during commit of statistics table changes.

Solution:
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- Disallow LOCK=NONE operation for the InnoDB statistics table.
The reasoning is that statistics tables are typically
rather small, so any blocking would be rather short.
Writes to the statistics tables should be a rare operation.