Re: MySQL versus Postgres

On Thu, Aug 12, 2010 at 10:53 AM, Greg Smith <greg(at)2ndquadrant(dot)com> wrote:
> I'm happy that we've already made
> a big step forward in helping new users here in that update.  At least now
> DBAs used to other systems who go looking for the "how do I set the size of
> the cache?" knob will stumble on reasonable advice in the manual, which was
> not the case before.  So I already expect this situation to be much better
> than it has ever been.

Thanks for that.

While writing the message, I remembered that the manual does not
stress much on the point, but on checking the latest version I found
it to be better. I should have checked the earlier versions also :-)

>> Can a final
>> "We recommend that you to set shared_buffers to 25% of system memory
>> you can allocate for PostgreSQL"
>> be included.
>>
>
> If only it were that easy.  25%, but only on a dedicated server, don't go
> above 8GB, limit to much less than that on Windows, and be extremely careful
> if you're writing heavily lest large checkpoints squash you.  Giving simple
> advice that people might follow without thinking about actually has some
> worst-case downsides that are worse than not tuning the server at all.
>

What does a migrating PHP/MySQL user do? If MySQL performs fast just
out of box (I have not used MySQL), what is different there? Do MySQL
defaults give better performance? How do they arrive at those
defaults?

Or is it a completely different system, which can not be adapted in PostgreSQL?

>> This makes Increasing work_mem is a complex calculation for a new user
>> trying out PostgreSQL.
>>
>
> Increasing work_mem is a complex calculation for everyone, not just new
> users.  If it were easy for anyone, we'd just bottle whatever experts do
> into the software directly.  I tried doing a round of that with pgtune, and
> it's still not quite right yet even after surveying everyone who had an
> opinion on the subject.

Again, what happens in MySQL? Do they have an equivalent parameter to
be set? and how it is set?

Thanks and regards,

Ma Sivakumar
http://masivakumar.blogspot.com