[tarantool-patches] Re: [PATCH v1 1/1] sql: fix tarantoolSqlite3TupleColumnFast

[Kirill Shcherbatov <kshcherbatov@tarantool.org>]

Hi! Thank you for research, I've included your conclusions to
the commit message.


The tarantoolSqlite3TupleColumnFast routine used to lookup
offset_slot in unallocated memory in some cases.
The assert with exact_field_count same as motivation to change
old correct assert with field_count in 7a8de28 is not correct.
assert(format->exact_field_count == 0 ||
       fieldno < format->exact_field_count);
The tarantoolSqlite3TupleColumnFast routine requires offset_slot
that has been allocated during tuple_format_create call. This
value is stored in indexed field with index that limited with
index_field_count that is <= field_count. Look at
tuple_format_alloc for more details.

The format in cursor triggering valid assertion has such
structure because first 4 tuples in _space: 257, 272, 276 and
280 have an old format of _space with only one field
(format->field_count == 1).
It happens because these 4 tuples are recovered not after tuple
with id 280 which stores actual format of _space. After tuple
280 is recovered, an actual format is set in struct space of
_space and all next tuples have full featured formats.

So for these 4 tuples tarantoolSqlite3TupleColumnFast can fail
even if a field exists, is indexed and has a name. Those
features are just described in a newer format.
(thank Gerold103 for problem explanation)

Closes #3772