Indeed, its a really annoying behavior that can lead to bad surprises
and similar issues can happen with command line tools that also supports
abbreviations such as the mysql CLI, mysqladmin or mysqldump (eg:
MDEV-7208).
The first solution, to put a prefix/suffix on options would break
compatibility with MySQL and other derivatives and add another level of
complexion that most of the users wont even bother try to understand.
The second solution seems the best to me : i think that such an option
should be added even on 10.0 and even if it would be disabled by default
on 10.0, there should be at least a warning throwed when an abbreviation
is used telling how it was really interpreted and that abbreviation use
is not recommended/deprecated ; that option would be enabled by default
on 10.1 or at least this option would be enabled on the default/example
my.cnf files supplied with MariaDB so it wouldnt break existing setups
and could be disabled for peoples that wants to stick with their bad habits.
The third solution makes sense if the second one requires much work to
be implemented and doesnt seems to be that important, a simple
deprecation warning for abbreviated commands on 10.0 would do the trick
then but i suspect that doing that, does takes almost as implementing
solution #2.
ps: i never used abbreviations and never saw configurations or users
using them (on purpose at least).
Le 05/01/2015 20:20, Sergei Golubchik a écrit :
Hi,
We've got a bit of a problem with command-line option prefixes in the
test suite. As you know, in MariaDB a command line option (the same
applies to my.cnf too) doesn't need to be specified completely, it's
sufficient to use an unambigous prefix of it.
For example, 'net-retry-count=5' in my.cnf can be abbreviated as
'net-ret=5'. But not as 'net-re=5', the latter will fail with an error
mysqld: ambiguous option '--net-re' (net_read_timeout, net_retry_count)
This is the historical behavior of MySQL since about 2002.
But it creates problems for plugins. InnoDB is particularly badly
affected - it has lots of I_S plugins that are prefixes of other I_S
plugins. For example:
INNODB_BUFFER_PAGE
INNODB_BUFFER_PAGE_LRU
...
INNODB_CMP
INNODB_CMPMEM
INNODB_CMPMEM_RESET
INNODB_CMP_PER_INDEX
INNODB_CMP_PER_INDEX_RESET
INNODB_CMP_RESET
...
INNODB_SYS_FOREIGN
INNODB_SYS_FOREIGN_COLS
...
INNODB_SYS_TABLES
INNODB_SYS_TABLESPACES
INNODB_SYS_TABLESTATS
also, it has plugins that match other plugin variables, like
INNODB_LOCKS and innodb_locks_unsafe_for_binlog.
As a result one cannot see or predict what these options will do.
For example --enable-innodb-buffer-page might enable INNODB_BUFFER_PAGE
plugin. Or it might enable INNODB_BUFFER_PAGE_LRU plugin - depending on
which plugin will loaded (and will see and consume the option) first.
And one cannot possibly disable INNODB_BUFFER_PAGE plugin, if the server
will try to load INNODB_BUFFER_PAGE_LRU first.
I see few solutions for this issue:
1. support a special suffix to option names that will disable prefix
matching, for example:
mysqld --enable-innodb-buffer-page!
this will not match innodb-buffer-page-lru, so it's unambiguous. Of
course, any dedicated character can be used, --enable-innodb-buffer-page$,
or even a prefix --enable-exact-innodb-buffer-page,
--enable-strict-innodb-buffer-page
2. add a special command-line option to disable prefix matching:
mysqld --disable-getopt-prefix-matching --enable-innodb-buffer-page
3. do like mysql-5.7 is doing and completely remove support for prefix
matching. In 5.7 one has to specified option names in full. I suspect
that this is likely to break many exising setups.
Opinions? Anybody cares about this obscure issue at all?
Regards,
Sergei
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