Currently, Alternator allows creating a table with a name up to 222
(max_table_name_length) characters in length. But if you do create
a table with such a long name, you can have some difficulties later:
You you will not be able to add Streams or GSI or LSI to that table,
because 222 is also the absolute maximum length Scylla tables can have
and the auxilliary tables we want to create (CDC log, materialized views)
will go over this absolute limit (max_auxiliary_table_name_length).
This is not nice. DynamoDB users assume that after successfully
creating a table, they can later - perhaps much later - decide to
add Streams or GSI to it, and today if they chose extremely long
names, they won't be able to do this.
So in this patch, we lower max_table_name_length from 222 to 192.
A user will not be able to create tables with longer names, but
the good news is that once successfully creating a table, it will
always be possible to enable Streams on it (the CDC log table has an
extra 15 bytes in its name, and 192 + 15 is less than 222), and it
will be possible to add GSIs with short enough names (if the GSI
name is 29 or less, 192 + 29 + 1 = 222).
This patch is a trivial one-line code change, but also includes the
corrected documentation of the limits, and a fix for one test that
previously checked that a table name with length 222 was allowed -
and now needs to check 192 because 222 is no longer allowed.
Note that if a user has existing tables and upgrades Scylla, it
is possible that some pre-existing Alternator tables might have
lengths over 192 (up to 222). This is fine - in the previous patches
we made sure that even in this case, all operations will still work
correctly on these old tables (by not not validating the name!), and
we also made sure that attempting to enable Streams may fail when
the name is too long (we do not remove those old checks in this patch,
and don't plan to remove them in the forseeable future).
Note that the limit we chose - 192 characters - is identical to the
table name limit we recently chose in CQL. It's nicer that we don't
need to memorize two different limits for Alternator and CQL.
Signed-off-by: Nadav Har'El <nyh@scylladb.com>
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