I'm skeptical that use-treads can every be very effective.
What order are the rows in? They are probably in PRIMARY KEY order, which means that the INSERTing threads will be fighting over similar spots in the table.
Is it I/O bound when it is single-threaded? If so, then there can't be any improvement with use-threads.
Suggest you file a bug with bugs.mysql.com. If nothing else, the documentation should say more than it does.
> -----Original Message-----
> From: Róbert Kohányi [mailto:kohanyi.robert@stripped]
> Sent: Tuesday, July 24, 2012 10:52 AM
> To: mysql@stripped
> Subject: mysqlimport --use-threads / mysqladmin processlist
> I'm in the middle of migrating an InnoDB database to an NDBCluster. I
> use mysqldump to first create two dumps, the first one contains only
> the database schema, the second one contains only tab delimited data
> (via mysqldump --tab). I edit my InnoDB schema here and there
> (ENGINE=InnoDB to ENGINE=NDB, etc.) import it and after this I import
> the InnoDB data *as is* using mysqlimport.
> I use it like this:
> mysqlimport --local --use-threads=4 db dir/*.txt
> (dir of course cotains the tab delimited data I dumped before.)
> The import starts, and I check its progress via mysqladmin, like this:
> mysqladmin --sleep=1 processlist
> this is what I see: http://pastebin.com/raw.php?i=M23fWVjc
> Only a single process seems to be loading my data. Is this what I
> *should* see, or, in my case using 4 threads, should I see four
> processes? I'm not asking which one will be faster, I'm just simply
> confused because I don't know what to expect. If I start four different
> mysqlimport processes, each one importing different files, then I can
> see four different process in the mysql processlist.
> If it's matters, here is my server version (I use the official
> Server version: 5.5.25a-ndb-7.2.7-gpl MySQL Cluster Community Server
> Kohányi Róbert
> MySQL General Mailing List
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