The crash scenario is as follows:
(1) A non-empty table exists.
(2) MDEV-15562 instant ADD/DROP/reorder has been invoked.
(3) Some purgeable undo log exists for the table.
(4) The table becomes empty, containing not even any delete-marked records,
only containing the hidden metadata record that was added in (2).
(5) An instant ADD/DROP/reorder column is executed, and the table
is emptied and the (2) metadata removed.
(6) Purge processes an undo log record from (3), which will refer to
a non-existent clustered index field, because the metadata that
was created in (2) was remoeved in (5).
We fix this by adjusting step (5) so that we will never remove the
MDEV-15562-style metadata record. Removing the MDEV-11369 metadata
record (instant ADD COLUMN to the end of the table) is completely
fine at any time when the table becomes empty, because
dict_index_t::n_fields will remain unchanged.
innobase_instant_try(): Never remove the MDEV-15562 metadata record.
page_cur_delete_rec(): Do not reset FIL_PAGE_TYPE when the
MDEV-15562 metadata record is being removed as part of
btr_cur_pessimistic_update() invoked by innobase_instant_try().
get_col_list_to_be_dropped() incorrectly returned uninteresting instantly
dropped column which was missing in a new dict_index_t
get_col_list_to_be_dropped(): rename to collect_columns_from_dropped_indexes
and stop return dropped columns
btr_push_update_extern_fields(): Add a parameter for the original number
of fields in the record before btr_cur_trim(). Assume that this function
will only be called for the clustered index, which is the only index
that can contain off-page columns.
trx_undo_prev_version_build(), btr_cur_pessimistic_update():
Only invoke btr_push_update_extern_fields() for the clustered index.
which are pointed to the table being altered
Problem:
========
InnoDB failed to change the column name present in foreign key cache
for instant add column. So it leads to column mismatch for the consecutive
rename of column.
Solution:
=========
Evict the foreign key information from cache and load the foreign
key information again for instant operation.
instant_alter_column_possible(): Do not support instantaneous removal
of NOT NULL if the table needs to be rebuilt for removing the hidden
FTS_DOC_ID column. This is not ideal and should ultimately be fixed
properly in MDEV-17459.
This basically is a duplicate of MDEV-18219, proving that the
assertion was not relaxed correctly.
dict_index_t::in_instant_init: A debug flag that will only be set in
btr_cur_instant_init_low() in order to suppress the assertion failure
in rec_init_offsets() for that code path only.
MDEV-11369 (instant ADD COLUMN) introduced a regression in the case the
leftmost leaf page of the clustered index is empty except for the
hidden metadata record.
btr_pcur_store_position(): If the only record in the leftmost leaf page
is the metadata record, store the position before the first user record
in the tree.
