Re: ASSM bug: slow INSERT after uncomitted DELETE
Date: Thu, 13 Aug 2009 10:37:31 +0100
"ca111026" <ca111026_at_gmail.com> wrote in message
> Sorry, how buffer busy waits are related to ASSM? I thought buffer
> busy waits ('read by other session' in later versions) is event that
> happens when multiple sessions are reading the same block from memory.
> This is why it is called 'buffer' (from 'buffer cache'). If table is
> "narrow" i.e. rows are short then there will be many rows per block,
> ASSM or no ASSM.
There are several causes of "buffer busy waits". They can also appear when two people want to modify the same block at the same - and if you have a table with freelists = 1, then there is only one insertion point available at a time, so concurrent inserts can see buffer busy waits.
There's a lot that could be said about multiple freelists, multiple freelist groups, ASSM, and RAC at this point and the various pros and cons of different technologies - but essentially ASSM was introduced to hide a common problem instead of instructing people about an existing solution.
-- Regards Jonathan Lewis http://jonathanlewis.wordpress.com Author: Cost Based Oracle: Fundamentals http://www.jlcomp.demon.co.uk/cbo_book/ind_book.html The Co-operative Oracle Users' FAQ http://www.jlcomp.demon.co.uk/faq/ind_faq.htmlReceived on Thu Aug 13 2009 - 04:37:31 CDT