Hi Kristian, Sergei.
What about this plan:
1. In 10.0:
a. Make "ALTER TABLE t1 FORCE" fully rebuild the table
and change old DECIMAL to new DECIMAL.
b. Keep "CHECK TABLE t1 FOR UPGRADE" to still return a line with
Msg_type=status and Msg_text=OK, but also add new
lines with Msg_type=note and Msg_text telling something like:
"The table 'db.table' has deprecated columns types incompatible with
Row-based replication."
"REPAIR TABLE is recommended. Note, this can take some time.".
c. mysql_upgrade will NOT upgrade tables with the old DECIMAL
automatically, because they will still be reported as "OK".
But mysql_upgrade should detects and prints the new notes
in the "CHECK TABLE t1 FOR UPGRADE" output.
d. Make the master running with --binlog-format=row refuse to do any
INSERT/UPDATE/ALTER or any other queries that can modify a table
with the old DECIMAL.
Also, make "mysqld --binlog-format=row" disallow queries like:
"CREATE TABLE t2 AS SELECT old_decimal FROM t1";
Make it print an error:
"The table 'db.table' has deprecated columns types incompatible
with Row-based replication."
(the same text with #b, but this time an error instead of a note).
Note, one will have to stop binary logging, upgrade the table,
and restart mysqld with binary logging again.
e. A SELECT from a table with the old DECIMAL should probably also
print a warning, to give the user another chance to know about the
problem.
f. Make INFORMATION_SCHEMA.COLUMNS somehow print information about the
deprecated data types (in DATA_TYPE or COLUMN_TYPE or
COLUMN_COMMENT).
2. In 10.1
Change "b" to return Msg_type=error and Mst_text=
"Table upgrade required. Please do "REPAIR TABLE `tablename`" or
dump/reload to fix it!"
This will also force mysql_upgrade to rebuild tables with the old
DECIMAL automatically.
Looks like a lot of work...
On 12/23/2014 02:17 PM, Alexander Barkov wrote:
Hi Kristian,
On 12/23/2014 02:08 PM, Kristian Nielsen wrote:
On Dec 22, Alexander Barkov wrote:
Hi Sergei, Kristian,
So, there are a lot of details in that bug and in the discussion, and
I did
not get a full overview of the problem, or what you were asking from
me, but
I'll try to answer as best I can.
Do I understand correctly that row-based replication writes directly the
internal representation of a DECIMAL column into the binlog event,
without
marking whether it is the old (pre-5.0) or the new format?
RBR does mark that this is the old pre-5.0 format.
so the slave knows that it is an old DECIMAL.
But it does not know which exactly DECIMAL(M,N),
because M and N are not available.
That indeed seems unfortunate. But I tend to agree that this is not
something
to try fixing, giving that this is a problem from 4.x days.
I would however suggest that in 10.1, we give an error on an attempt
to binlog
a row-based event with the old-format DECIMAL. The error should
explain that
the table needs to be converted to the new format to work with row-based
replication.
Good idea.
I'd also do the same with the old TIME/DATETIME/TIMESTAMP types with
fractional precision, as they have the same problem.
I think that CHECK TABLE..FOR UPDATE should report
the problem with long DECIMALs in a warning.
mysql_upgrade should also warn about the problem,
but should not touch these tables.
I think that sounds reasonable.
I assume that fixing the internal types requires a full table rebuild?
Yes.
Full table rebuild can be extremely painful on large tables. So it is
rather
dangerous to add that in a minor stable release. For example, the
Debian/Ubuntu packages run mysql_upgrade automatically, and minor stable
releases arrive as security fixes.
So one could argue for fixing in 10.1 from this point of view.
Maybe / hopefully, given that this is a pre-5.0 problem, the issue is not
_that_ important one way or the other.
Perhaps we chould fix this in 10.1, and add an error in earlier versions
on attempt to RBR-binlog a table with the old DECIMAL.
- Kristian.
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