Re: Blocks read for index scans

Поиск
Список
Период
Сортировка
От Terje Elde
Тема Re: Blocks read for index scans
Дата
Msg-id 4445A1DF.6000705@elde.net
обсуждение исходный текст
Ответ на Re: Blocks read for index scans  ("Jim C. Nasby" <jnasby@pervasive.com>)
Ответы Re: Blocks read for index scans  ("Jim C. Nasby" <jnasby@pervasive.com>)
Список pgsql-performance
Jim C. Nasby wrote:
>> That said, it's the transactions against disk that typically matter.  On
>> FreeBSD, you can get an impression of this using 'systat -vmstat', and
>> watch the KB/t column for your drives.
>>
>
> On a related note, you know of any way to determine the breakdown
> between read activity and write activity on FreeBSD? vmstat, systat,
> iostat all only return aggregate info. :(
>


Can't think of a right way to do this ATM, but for a lab-type setup to
get an idea, you could set up a gmirror volume, then choose a balancing
algorithm to only read from one of the disks.  The effect should be that
writes go to both, while reads only go to one.  Activity on the
write-only disk would give you an idea of the write activity, and
(read/write disk - write-only disk) would give you an idea of the
reads.  I have to admit though, seems like quite a bit of hassle, and
I'm not sure how good the numbers would be, given that at least some of
the info (KB/transaction) are totals, it'd require a bit of math to get
decent numbers.  But at least it's something.

Terje



В списке pgsql-performance по дате отправления:

Предыдущее
От: Christopher Kings-Lynne
Дата:
Сообщение: Re: SELECT FOR UPDATE performance is bad
Следующее
От: Mark Kirkwood
Дата:
Сообщение: Re: merge>hash>loop