[mythtv-users] my experience with myth on a solid state drive

[Steven Adeff]

On Thu, Jan 5, 2012 at 3:20 PM, Dan Wilga
<mythtv-users2 at dwilga-linux1.amherst.edu> wrote:
> While I don't necessarily disagree with you on the other points, I have
> a suggestion regarding this one:
>
> On 1/5/12 11:20 AM, Ronald Frazier wrote:
>> So what was doing all the writes to /tmp? Several times an hour, myth
>> recalculates its schedule. When it does, it uses about 500MB of
>> temporary mysql tables. That alone was responsible for over 90% of the
>> writes on the SSD. So instead, I created /tmp as a tmpfs partition.
>> I've got 2GB of ram, so that gives /tmp up to 1GB to use.
>
> You could also just use this in your my.cnf to achieve the same effect:
>
> tmpdir = /dev/shm
>
> However, in the case of MySQL, it's even faster if you prevent it from
> ever using temporary files. You can do this by throwing RAM at it with
> these two parameters in my.cnf:
>
> tmp_table_size
> max_heap_table_size
>
> The default for the heap is a ridiculously small 16M. In practice, I've
> found that MySQL will free up RAM it's not actively using, once it's
> done with the temporary, in-RAM tables. For more info, see:
>
> http://dev.mysql.com/doc/refman/5.1/en/internal-temporary-tables.html

ok, so looking into this further,

tmp_table_size
Default 	system dependent
max_heap_table_size
Default 	16777216 (regardless of 32/64bit)

So what your suggesting is to raise the value of both to a size that
will allow for these temporary tables to reside in memory, which as
Ronald suggests, is just over 500MB? (the documentation says the
smaller of the two values, in case anyone wants to run one at a higher
value)

Then I assume mysql frees this memory up once it's done with it?

-- 
Steve
http://www.mythtv.org/wiki/User:Steveadeff
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