maria-discuss team mailing list archive

[Guillaume Lefranc <guillaume@xxxxxxxxxxxx>]

Hi Sergey,

I might be able to try again, though I moved to a different database at
this point.
But the phenomenon I observed was very high IO for several hours, and the
table was still not dropped and recreated.
if TRUNCATE TABLE just unlinks the data files we shouldn't observe that
behavior.

Thanks
Guillaume

Le dim. 9 juil. 2017 à 22:34, Sergey Petrunia <sergey@xxxxxxxxxxx> a écrit :

> Hello,
>
> On Fri, Jun 30, 2017 at 08:58:08AM -0700, MARK CALLAGHAN wrote:
> > This started as a question on a MyRocks list. MyRocks comes from MariaDB
> in
> > this case and the code that determines whether the truncate table fast
> path
> > is used looks different in MariaDB than in FB MySQL. By "fast path" for
> > truncate I mean the use of drop/recreate for truncate. The slow path is
> > delete one row at a time. In this case, truncate is doing delete one row
> at
> > a time for MyRocks in MariaDB but drop/recreate in FB MySQL.
> >
> > https://groups.google.com/forum/#!topic/myrocks-dev/dhweTwN-9xg
>
> I didn't try to measure speed, but when I debugged TRUNCATE statements in
> MariaDB and MySQL, I see they both call ha_rocksdb::create(), which
> re-creates
> the table.
>
> MariaDB 10.2:
> https://gist.github.com/spetrunia/35738308469e27381056c6e90a5e2ce6
> FB/MySQL-5.6
> <https://gist.github.com/spetrunia/35738308469e27381056c6e90a5e2ce6FB/MySQL-5.6>:
> https://gist.github.com/spetrunia/18096aa8ec965dc37a502496217c0bb0
>
> MariaDB also prints these statements into stderr
>
> 2017-07-08  2:53:10 140737294370560 [Note] RocksDB: Begin filtering
> dropped index (0,261)
> 2017-07-08  2:53:10 140736961083136 [Note] RocksDB: Finished filtering
> dropped index (0,261)
>
> which is another indication that there is no row-by-row deletion.
>
> I was using current github trees of both FB/mysql-5.6 and MariaDB-10.2.
> Maybe
> that is the reason... I'll do more checks.
>
>
> BR
>  Sergei
> --
> Sergei Petrunia, Software Developer
> MariaDB Corporation | Skype: sergefp | Blog: http://s.petrunia.net/blog
>
>
>
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