Обсуждение: Expensive log_line_prefix ?
In 9.1.x
Are there any "extra" costs to logging all this cool stuff ?
log_line_prefix = '%m %a %u %p %c %m %v %x'
Are any of these expensive ?
Or is the only cost the number of bytes that the textual representation of their values take in the written log file ?
Thanks,
-dvs-
On Thu, Oct 11, 2012 at 12:19 PM, Sahagian, David <david.sahagian@emc.com> wrote: > Are there any "extra" costs to logging all this cool stuff ? > > log_line_prefix = '%m %a %u %p %c %m %v %x' The formatting cost only but it is so insignificant that does not worth bothering with it. -- Sergey Konoplev a database and software architect http://www.linkedin.com/in/grayhemp Jabber: gray.ru@gmail.com Skype: gray-hemp Phone: +14158679984
On 10/11/12 2:57 PM, Sergey Konoplev wrote: > On Thu, Oct 11, 2012 at 12:19 PM, Sahagian, David > <david.sahagian@emc.com> wrote: >> >Are there any "extra" costs to logging all this cool stuff ? >> > >> > log_line_prefix = '%m %a %u %p %c %m %v %x' > The formatting cost only but it is so insignificant that does not > worth bothering with it. i'd think the time spent writing the extra output to the log file would be the most significant part of it, along with any disk IO contention if those logs are on the same physical storage as the database. -- john r pierce N 37, W 122 santa cruz ca mid-left coast
Sergey Konoplev <gray.ru@gmail.com> writes:
> On Thu, Oct 11, 2012 at 12:19 PM, Sahagian, David
> <david.sahagian@emc.com> wrote:
>> Are there any "extra" costs to logging all this cool stuff ?
>>
>> log_line_prefix = '%m %a %u %p %c %m %v %x'
> The formatting cost only but it is so insignificant that does not
> worth bothering with it.
IIRC, %m would imply a gettimeofday call, which might be expensive
depending on your OS and hardware. I think all the other info is
"just sitting around", though.
regards, tom lane
Tom Lane escribió: > Sergey Konoplev <gray.ru@gmail.com> writes: > > On Thu, Oct 11, 2012 at 12:19 PM, Sahagian, David > > <david.sahagian@emc.com> wrote: > >> Are there any "extra" costs to logging all this cool stuff ? > >> > >> log_line_prefix = '%m %a %u %p %c %m %v %x' > > > The formatting cost only but it is so insignificant that does not > > worth bothering with it. > > IIRC, %m would imply a gettimeofday call, which might be expensive > depending on your OS and hardware. I think all the other info is > "just sitting around", though. Yeah, and having two %m means two gettimeofday calls. Also, %c sort of implies %p, so having both is probably just a waste. One other point is that it's probably a good idea to put in a %q in there so that processes that don't have things like %v, %x don't have to print a bunch of zeros (and also to prevent %a, %u from adding spaces unnecessarily). -- Álvaro Herrera http://www.2ndQuadrant.com/ PostgreSQL Development, 24x7 Support, Training & Services