Let us introduce the parameter innodb_read_only_compressed
that is ON by default, making any ROW_FORMAT=COMPRESSED tables
read-only.
I developed the ROW_FORMAT=COMPRESSED format based on
Heikki Tuuri's rough design between 2005 and 2008. It might
have been a good idea back then, but no proper benchmarks were
ever run to validate the design or the implementation.
The format has been more or less obsolete for years.
It limits innodb_page_size to 16384 bytes (the default),
and instant ALTER TABLE is not supported.
This is the first step towards deprecating and removing
write support for ROW_FORMAT=COMPRESSED tables.
Allow instant changes of columns in ROW_FORMAT=REDUNDANT
from NOT NULL to NULL.
Later, this may be implemented for ROW_FORMAT=COMPACT or DYNAMIC,
but in that case any indexes on the table must be rebuilt.
dict_table_t::prepare_instant(): Add some debug assertions,
and relax a debug assertion so that the number of fields is
allowed not to change.
dict_index_t::instant_add_field(): Relax a debug assertion,
allowing a column to change from NOT NULL to NULL.
dict_table_t::instant_column(): Add debug assertions.
instant_alter_column_possible(): Allow ALTER_COLUMN_NULLABLE
when applicable.
innodb_insert_sys_columns(): Add the parameter bool update=false
to run UPDATE instead of INSERT.
innobase_instant_add_col(): Remove; let the only caller invoke
innodb_insert_sys_columns() directly.
innobase_instant_try(): Update the SYS_COLUMNS record if the
column is changed. Only convert the table to the instant ALTER TABLE
format if necessary. For ALTER_COLUMN_NULLABLE in ROW_FORMAT=REDUNDANT,
there is no data format change.
