Re: checkpointer continuous flushing

On Sun, Aug 23, 2015 at 12:33 PM, Fabien COELHO <coelho(at)cri(dot)ensmp(dot)fr> wrote:

>
> Hello Amit,
>
> I have tried your scripts and found some problem while using avg.py
>> script.
>> grep 'progress:' test_medium4_FW_off.out | cut -d' ' -f4 | ./avg.py
>> --limit=10 --length=300
>> : No such file or directory
>>
>
> I didn't get chance to poke into avg.py script (the command without
>> avg.py works fine). Python version on the m/c, I planned to test is
>> Python 2.7.5.
>>
>
> Strange... What does "/usr/bin/env python" say?

Python 2.7.5 (default, Apr 9 2015, 11:07:29)
[GCC 4.8.3 20140911 (Red Hat 4.8.3-9)] on linux2
Type "help", "copyright", "credits" or "license" for more information.
>>>

> Can the script be started on its own at all?

I have tried like below which results in same error, also I tried few
other variations but could not succeed.
./avg.py
: No such file or directory

>
> Here, I think above calculation can go for toss if backend or bgwriter
>> starts writing buffers when checkpoint is in progress. The tablespace
>> written parameter won't be able to consider the one's written by backends
>> or bgwriter.
>>
>
> Sure... This is *already* the case with the current checkpointer, the
> schedule is performed with respect to the initial number of buffers it
> think it will have to write, and if someone else writes these buffers then
> the schedule is skewed a little bit, or more... I have not changed this
> logic, but I extended it to handle several tablespaces.
>
>
I don't know how good or bad it is to build further on somewhat skewed
logic, but the point is that unless it is required why to use it.

> I do not think that Heikki version worked wrt to balancing writes over
> tablespaces,

I also think that it doesn't balances over tablespaces, but the question
is why do we need to balance over tablespaces, can we reliably
predict in someway which indicates that performing balancing over
tablespace can help the workload. I think here we are doing more
engineering than required for this patch.

> and I'm not sure it worked at all.

Okay, his version might have some bugs, but then those could be
fixed as well.

With Regards,
Amit Kapila.
EnterpriseDB: http://www.enterprisedb.com