maria-discuss team mailing list archive

[Marko Mäkelä <marko.makela@xxxxxxxxxxx>]

Hi Rajat,

Foreign keys in MySQL or MariaDB are a bit of a second-class citizen, only
implemented inside InnoDB. Even the foreign key metadata is only stored
inside InnoDB. Also, foreign keys only work between InnoDB tables.

I think that once those issues have been fixed (once we have foreign keys
implemented avobe the storage engine layer, working on any transactional
tables), it should be more feasible to implement a multi-table truncate
operation. We certainly want the operation to be atomic, so it would have
to work something like this:

1. Lock all the tables, and check that all criteria are met.
2. Atomically write transaction log records to TRUNCATE every table.
3. Truncate the tables.
4. Remove the transaction log records.
5. Unlock the tables and return to the client.

Even if we ignore other storage engines than InnoDB, step 2 is a problem.
The logging of TRUNCATE was rewritten in WL#6501 in MySQL 5.7 in a way that
makes it challenging for tools like Mariabackup or xtrabackup to work. That
logging would have to be rewritten. I think that we need a transactional
"ddl_fixup" table that could also be used for implementing transactional,
fully crash-safe DDL operations with .frm files.

As you can see, the task is rather complex. There are many things that
would have to be refactored first. I do not know how much of this we can do
within the 10.4 release. Soon we will release MariaDB 10.3 as beta, to be
released as GA some time next year. This definitely cannot be done in 10.3.

Best regards,

Marko

On Sat, Nov 11, 2017 at 4:38 PM, Rajat Rawat <rajatrawat1997@xxxxxxxxx>
wrote:

> Respected Sir/Mam
>
>
>
> Hello, Myself Rajat from India. I wanted to contribute/work with Mariadb.
>
>
>
> As we know that Mariadb dosen’t have cascade truncate function available
> yet, so I want to contribute to Mariadb towards this topic.
>
> My topic is “*Cascade Truncate*”.
>
>
>
> Since we can’t truncate the parent table unless the referential integrity
> constraints are present in the child table also. Hence, we can do a way
> that we can provide a command that truncate the child table as well.
>
>
> This enhancement is already provided in the Oracle Database in their 12c
> Version, by using the *truncate cascade* command.
>
>
>
> It is better to truncate the child table at the time when we want to
> truncate our parent table.
>
>
> As we know that we have already on Delete Cascade command available, but
> that command works only row by row and not for all rows at one time.
>
>   So, at one time if we want to truncate our whole table then *Cascade
> Truncate* is a better Option.
>
>
>
> That’s all about my proposal. If you like my proposal, then let me know
> about about it.
>
>
>
> I am very eager to contribute for you. I also forked and downloaded on my
> local machine, the file of Maraidb which is available on Github,  and
> currently I am reading/understanding all the patches, but I am confused
> with only 1 thing that from where should I start.
>
>
>
> So, if you like proposal then let me know about it and please guide me
> that from where should I start contributing for it.
>
>
>
> My skills: C, C++, Java, SQL, PL/SQL
>
> Achievement: Oracle Certified Associate Java Programmer SE 7.
>
>
>
> By  contributing for you I will definitely learn many new things and
> implement my ideas, while working with you.
>
>
>
> Hope I could be of any help for you.
>
>
>
> Your sincerely
>
> Rajat
>
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-- 
Marko Mäkelä, Lead Developer InnoDB
MariaDB Corporation