The variable innodb_dedicated_server is explained in detail when the feature was announced (2017-08-24):
It's just a shorthand for a number of tuning options. The new variable doesn't improve performance in any special way, it's exactly the same as setting those other tuning options yourself.
I’m sorry, but I don’t like this feature at all. I understand the goal
of improving the out-of-the-box experience for naive users, but I
don’t think this solution will be successful at this goal.
Trying to pre-tune a MySQL installation with some formula is a
one-size-fits-all solution, and these kinds of solutions are
unreliable. We can recall examples of other products that have tried
to do this, but eventually removed their auto-tuning features.
It’s not a good assumption that the buffer pool needs as much physical
RAM as you can afford. You already know this, because you need the
innodb_dedicated_server option. Rick mentioned the possibility that
the dataset is already smaller than RAM. In this case, adding more RAM
has little or no benefit.
Many naive users mistakenly believe (after reading some blog) that
increasing RAM allocation always increases performance. It’s difficult
to explain to them why this is not true.
Likewise innodb log file. We assume that bigger is better, because of
benchmarks showing that heavy write traffic benefits from bigger log
files, because of delaying checkpoints. But what if you don’t have
heavy write traffic? What if you use MySQL for a blog or a CMS that is
99% reads? The large log file is unnecessary. Sizing it for an assumed
workload or dataset size has a high chance of being the wrong choice
for tuning.
I understand the difficulty of asking users questions during
installation. I recently did a project automating MySQL provisioning
with apt. It was annoying having to figure out debconf to work around
the installation prompts that do exist (btw, please document MySQL’s
debconf variables!).
There’s also the problem that even if you do prompt the user for
information, they don’t know the answers to the questions. This is
especially true of the naive users that you’re targeting with this
feature.
If the installer asks “Do you use MySQL on a dedicated server?” do
they even know what this means? They might think “dedicated” is simply
the opposite of shared hosting.
If the installer asks “Do you want to use all available memory on this
system?” you will be surprised at how many users think “memory” refers
to disk space, not RAM.
In short: (1) Using formulas to tune MySQL is error-prone. (2) Asking
users to make choices without information is error-prone.
I have an alternative suggestion: Make it easier for users to become
less naive about their choices.
I think users need a kind of friendly cheat-sheet or infographic of
how to make tuning decisions. This could include a list of questions
about their data size and workload, and then a list of performance
indicators to monitor and measure, like buffer pool page create rate,
and log file write rate. Give tips on how to measure these things,
what config options to change, and then how to measure again to verify
that the change had the desired effect.
A simple monitoring tool would also be useful. Nothing so
sophisticated as PMM or VividCortex for long-term trending, but
something more like pt-mext for quick, ephemeral measurements.
The only thing the installation process needs to do is tell the user
that tuning is a thing they need to do (many users don’t realize
this), and refer them to the cheat-sheet documentation.
