maria-developers team mailing list archive

[Jeremy Cole <jeremycole@xxxxxxxxxx>]

Haha, this is the code in storage/innobase/handler/ha_innodb.cc:

3260 ▸       if (innobase_buffer_pool_instances == 0) {
3261 ▸       ▸       innobase_buffer_pool_instances = 8;
3262
3263 #if defined(__WIN__) && !defined(_WIN64)
3264 ▸       ▸       if (innobase_buffer_pool_size > 1331 * 1024 * 1024) {
3265 ▸       ▸       ▸       innobase_buffer_pool_instances
3266 ▸       ▸       ▸       ▸       = ut_min(MAX_BUFFER_POOLS,
3267 ▸       ▸       ▸       ▸       ▸       (long)
(innobase_buffer_pool_size
3268 ▸       ▸       ▸       ▸       ▸       / (128 * 1024 * 1024)));
3269 ▸       ▸       }
3270 #endif /* defined(__WIN__) && !defined(_WIN64) */
3271 ▸       }

So basically 0 means 8 unless you're on 32-bit Windows where it means one
per 128 MiB of buffer pool, but only if the buffer pool is bigger than 1.3
GiB.

Gotta love the lack of comments.

Basically 0 is the default for the actual parameters, but it's fixed up to
8 at runtime. So the --help output will show 0 even though it will end up
with 8 (or N). It's basically using 0 as a way to say "the user didn't
specify, so figure it out".

Regards,

Jeremy



On Wed, Aug 6, 2014 at 2:26 PM, Daniel Bartholomew <dbart@xxxxxxxxxxx>
wrote:

> I was chatting with some folks on IRC and someone pointed this out to me.
>
> On the "Upgrading From MariaDB 5.5 to MariaDB 10.0" page, it says that
> the new default value for innodb-buffer-pool-instances is '0':
>
> https://mariadb.com/kb/en/upgrading-from-mariadb-55-to-mariadb-100/
>
> And when I run the following, it says the default is indeed '0':
>
> mysqld --no-defaults --verbose --help | grep innodb-buffer-pool-instances
> ...
> innodb-buffer-pool-instances                               0
>
>
> But when I'm in the client, I get the following:
>
> MariaDB [(none)]> select @@innodb_buffer_pool_instances;
> +--------------------------------+
> | @@innodb_buffer_pool_instances |
> +--------------------------------+
> |                              8 |
> +--------------------------------+
>
> So when innodb-buffer-pool-instances is set to '0', does that mean the
> actual value is dynamic or calculated in some way based on my other
> settings?
>
> Just trying to understand what's going on, and once I do, use it to
> update the XtraDB/InnoDB buffer-pool page (which doesn't appear to
> have been updated for 10.0).
>
> https://mariadb.com/kb/en/xtradbinnodb-buffer-pool/
>
>
> Thanks!
>
> --
> Daniel Bartholomew, MariaDB Release Manager
> MariaDB | http://mariadb.com
>
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