Re: Background Writer and performances

Hello List,

I have uploaded charts on a ftp server.
You can access to these 6 graphs by doing
ftp visibull.frec.bull.fr
login : ftp
password : ftp
You are under the "/" directory and with "ls" command you see the
directory "PGS_bgwriter".

In this directory, the 3 charts joined to this e-mail and called
“DiskActivity_defaultBgwriter.png”, “DiskIO_defaultBgwriter.png”,
“DiskWriteThroughput_defaultBgwriter.png” are obtained by setting :
- bgwriter_delay = 200
- bgwriter_lru_percent = 1.0
- bgwriter_lru_maxpages = 5
- bgwriter_all_percent = 0.333
- bgwriter_all_maxpages = 5

and the 3 charts joined to this e-mail and called
“DiskActivity_maxBgwriter.png”, “DiskIO_maxBgwriter.png”,
“DiskWriteThroughput_maxBgwriter.png” are obtained by setting :
- bgwriter_delay = 50
- bgwriter_lru_percent = 100
- bgwriter_lru_maxpages = 1000
- bgwriter_all_percent = 100
- bgwriter_all_maxpages = 1000

I hope someone will give me explanations on the background writer.
Thank you very much for your help.

Regards,
Alexandra DANTE

Martijn van Oosterhout wrote:

>On Mon, Jul 10, 2006 at 02:56:48PM +0200, DANTE Alexandra wrote:
>
>
>>**********************************
>>I would like to send charts to show you exactly what happens on the
>>server but, with the pictures, this e-mail is not posted on the mailing
>>list.
>>I can send charts to a personal e-mail adress if needed.
>>**********************************
>>
>>
>
>The best idea is to upload them to a website.
>
>
>
>>By comparing the charts, I can see that the checkpoints are less
>>expensive in term of Disk activity, IO/s and disk write throughput when
>>the parameters are set to the maximum values but I don?t not reach to
>>have constant disk IO/s, disk activity, disk write throughput before and
>>after a checkpoint. I was expecting to see more activity on the disks
>>during the bench (and not only a peak during the checkpoint) when the
>>parameters are set to the maximum values. Is it possible ?
>>
>>
>
>I have very little experience with the bgwriter, but on the whole, I
>don't think the bgwriter will change the total number of I/Os. Rather,
>it changes the timing to make them more consistant and the load more
>even.
>
>However, reading the descriptions, there's always going to be an
>unavoidable spike at checkpoint time because the checkpoint actually
>needs to sync() the data to disk, whereas the bgwriter merely queues it
>to the kernel.
>
>
>
>>Have you already experimented the Background Writer ? What results could
>>I obtain by setting properly the parameters ?bgwriter_xxx? ? Could
>>somenone explain me how I can used it ?
>>
>>
>
>Looking arond I mostly see that people are still testing. I'm not
>really in a position to know however...
>
>Have a nice day,
>
>