Re: pg_stat_statements

I understand there must be "some" overhead because we're collecting
extra info.   I'm curious if there're considerable amount of overhead
to the users who don't want such additional trance.

2008/6/16 ITAGAKI Takahiro <itagaki.takahiro@oss.ntt.co.jp>:
>
> Robert Treat <xzilla@users.sourceforge.net> wrote:
>
>> On Friday 13 June 2008 12:58:22 Josh Berkus wrote:
>> > I can see how this would be useful, but I can also see that it could be a
>> > huge performance burden when activated.  So it couldn't be part of the
>> > standard statistics collection.
>>
>> A lower overhead way to get at this type of information is to quantize dtrace
>> results over a specific period of time.  Much nicer than doing the whole
>> logging/analyze piece.
>
> DTrace is disabled in most installation as default, and cannot be used in
> some platforms (especially I want to use the feature in Linux). I think
> DTrace is known as a tool for developers, but not for DBAs. However,
> statement logging is required by DBAs who used to use STATSPACK in Oracle.
>
>
> I will try to measure overheads of logging in some implementation:
>  1. Log statements and dump them into server logs.
>  2. Log statements and filter them before to be written.
>  3. Store statements in shared memory.
>
> I know 1 is slow, but I don't know what part of it is really slow;
> If the reason is to write statements into disks, 2 would be a solution.
> 3 will be needed if sending statements to loggger itself is the reason
> of the overhead.
>
> Regards,
> ---
> ITAGAKI Takahiro
> NTT Open Source Software Center
>
>
>
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-- 
------
Koichi Suzuki