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debugging MDEV-5932, wrong result set for tokudb



TokuDB generates an empty result set for a select with sub-select, but
generated a non-empty result set for the same query when creating a new
table.  The result set should be the same in both cases.  What is going on
here?  InnoDB computes an empty result set for both cases.

I traced the problem to the tokudb::index_read function.  The
tokudb::index_read does not handle the null byte key prefix.
 Unfortunately, I do not understand how the null byte (byte 0) in the key
handed to the ::index_read function is supposed to work.   Most of the
time, the value of this byte is 0.  Sometimes it is set to 1.  How should
the storage engine work WRT this?

BTW, this problem exists with TokuDB in MySQL 5.5.36, MySQL 5.6.16.  I have
not been able to consistently see this on MariaDB 5.5.36 for some reason.
 In any case, I am interested in how the handler's index_read function is
supposed to process the null byte.


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