[HyperDB] Partitioning wpmu data

Callum Macdonald lists.automattic.com at callum-macdonald.com
Thu Apr 23 18:57:29 GMT 2009

As Andy said, HyperDB is about on the money for what you want.

The biggest challenge you'll face will be moving the data. You have 11k
tables in one database right now, you need to move those to new
databases. The MultiDB class uses the same method as HyperDB did
originally, 4096 databases, first 3 digits of the md5 of the blog_id
(the NNN number).

I think your best bet will be to use HyperDB and create your own system
for managing which blog is in which database (maybe a lookup table like
Andy mentioned). That way you'll be able to migrate the data over time.

Other options that occur to me:

Migrate all the data at once. Take the whole system down for a few hours
and move all the tables as you need to. Pray nothing goes wrong. :-)

You could add some logic that checks if the table is found in the new
target database, and if not, fall back on the global database. That
would allow you to move blogs one at a time, without changing any code.
If the blog tables are in the new database, the queries go there, if
not, the queries go to the master table.

If you're looking for help, you could speak to the guys at Incsub. I'm a
(present and about to be) retired staffer there, so I'm biased. :-)

Best of luck with the project.

Cheers - Callum.

On Thu, 2009-04-23 at 10:32 -0700, Felix Gushansky wrote:
> Hello, folks. We have just inherited the site that uses wordpress MU (ver
> 2.5.1) with MySQL 5 on the back. Soon we have learned that the blog db is
> huge. Not size wise necessarily (it is slightly over a gig), but table wise.
> That db contains over 11,000 tables with the total of over 40,000 files in
> the same directory. That hugely affects performance AND maintenance ­ to the
> point in fact that we can not backup the db using mysqldump. We had to write
> a script dumping a table at a time.
> So, we need to scale somehow. That¹s why he have looked at HyperDB, which
> seems to have been built just for that. However, the problem we are seeing
> is that in our case the tables in the blog db are created and named
> dynamically. For each new user wpmu creates multiple tables (8?) in the
> database and names them like wp_<nnnn>_comments, wp_<nnnn>_links,
> wp_<nnnn>_options, wp_<nnnn>_postmeta, wp_<nnnn>_posts, etc, where <nnnn> is
> a four digit integer. Can we take advantage of HyperDB in this case? And if
> not what are our options?
> Thanks very much folks. Your help is very much appreciated.
> -- Felix
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