btr_cur_optimistic_update(), btr_cur_pessimistic_update(): Do not trim
the 'default row' record.

innobase_instant_add_try(): Compute and apply the update vector for
the 'default row'.

FIXME: The rollback of the 'default row' operations (that is, the
ROLLBACK of the ALTER TABLE…ADD COLUMN operation) has not been tested
and is unlikely to work. We need a test that flushes the redo log
and kills the server at the end of innobase_instant_add_try(), before
the ALTER TABLE transaction is committed.

btr_cur_instant_init_low(): Read and validate the 'default row'

btr_cur_instant_root_init(): Avoid tripping a debug assertion

innobase_add_instant_try(): Use field_ref_zero for empty values.
Tolerate the hidden FTS_DOC_ID column.

The space management and recovery of operations on off-page columns
relies on the undo log records. Inserting off-page columns during
rollback could break this.

The solution to the rollback problem is simple: Do not duplicate
'default row' data in individual records. In this way, the ROLLBACK
of an UPDATE to a record that was originally written before instant
ADD COLUMN, would never have to insert off-page records, even if
there were instantly added BLOB columns with long DEFAULT values.
This will also reduce space consumption (a simple form of compression).

dtuple_t::trim(index): Omit a redundant suffix of an index tuple right
before insert or update. After instant ADD COLUMN, if the last fields
of a clustered index tuple match the 'default row', there will be no
need to store them. While trimming the entry, we must hold a page latch,
so that the table cannot be emptied and the 'default row' be deleted.

btr_cur_optimistic_update(), btr_cur_pessimistic_update(),
row_upd_clust_rec_by_insert(), row_ins_clust_index_entry_low():
Invoke dtuple_t::trim() if needed.

row_ins_clust_index_entry(): Restore dtuple_t::n_fields after calling
row_ins_clust_index_entry_low().

rec_get_converted_size(), rec_get_converted_size_comp(): Allow the number
of fields to be between n_core_fields and n_fields.

rec_convert_dtuple_to_rec_comp(): Assign the status bits based on the
number of fields.

innobase_add_instant_try(): If the table is empty, remove the 'default row'
instead of adding one.

dict_index_t::commit_instant_copy(): Allow !instant.is_instant() for
the clustered index.

ha_innobase_inplace_ctx::commit_instant(): Allow !instant_table->is_instant()

row_sel_try_search_shortcut_for_mysql(): Skip the 'default row', like row_sel_try_search_shortcut() does

row_upd_changes_field_size_or_external(): Revert some unnecessary
changes, and assert that the update vector does not contain the
magic value UNIV_SQL_DEFAULT.

row_upd_rec_in_place(): Remove a redundant assertion.
rec_set_nth_field() already asserts the same.

row_upd_build_sec_rec_difference_binary(): Assert that there are
no default values in a secondary index tuple.

The ALGORITHM=INPLACE interface is not accessible to temporary tables.
Therefore, instant ADD COLUMN cannot be used either.

dict_table_t::is_temporary(): New predicate.

dict_table_is_temporary(): Define as a wrapper macro.

In the temporary file that is applied by row_log_table_apply(),
we must identify whether the records contain the extra header for
instantly added columns. For now, we will allocate an additional byte
for this for ROW_T_INSERT and ROW_T_UPDATE records when the source table
has been subject to instant ADD COLUMN. The ROW_T_DELETE records are
fine, as they will be converted and will only contain 'core' columns
(PRIMARY KEY and some system columns) that are converted from dtuple_t.

rec_get_converted_size_temp(), rec_init_offsets_temp(),
rec_convert_dtuple_to_temp(): Add the parameter 'status'.

rec_set_n_add_field(): Simplify the interface to resemble
rec_get_n_add_field().

rec_init_offsets_comp_ordinary(): Handle the new rec_leaf_format
constant REC_LEAF_TEMP_COLUMNS_ADDED.

rec_get_converted_size_comp_prefix_low(),
rec_convert_dtuple_to_rec_comp(): Handle
index->is_instant() for both temp and !temp.

Ensure that no adaptive hash index exists for any system tables,
so that the blocked TRUNCATE TABLE t1 will not block the concurrent
TRUNCATE TABLE t2.

Ensure that no adaptive hash index exists for any system tables,
so that the blocked TRUNCATE TABLE t1 will not block the concurrent
TRUNCATE TABLE t2.

Made a few links in README.md secure (https).

This bug is a regression caused by the code refactoring in
commit f5a833c3. It was not present
in any release of the MariaDB server. The bug affects table-rebuilding
ALTER TABLE when the source table is in ROW_FORMAT=REDUNDANT and
contains no virtual columns.

row_log_table_low_redundant(): Log virtual column data only if
virtual columns are present.

In TRUNCATE TABLE, clear the 'instant' status of a table. TODO: Do the same when the table becomes empty

dict_col_t::remove_instant(): Remove the instantness of a column.

dict_index_t::remove_instant(): Remove the instantness of a clustered index.