what does kgl stand for?
srivenu_at_hotmail.com (srivenu) wrote in message news:<1a68177.0405262359.2afd3545_at_posting.google.com>...
> ryan,
> i may be wrong in making some of these observations, but i would
> anyway.
> > Is buffer_gets the same thing as 'consistent gets' in autotrace outputs? Its
> > how many latch gets oracle takes on the buffer cache?
>
> buffer gets can be both consistent gets and db block gets.
> There are basically 2 types of latches protecting the access of Buffer
> Cache, they are cache buffers lru chain latches & cache buffers chains
> latches.
> Every access to a buffer (or buffer header), even a lookup on the
> cache buffer hash chain needs to take the correspoding cache buffers
> chains latch. This latch is taken at several points in oracle code (I
> think you can see all those paths using this query - select "WHERE"
> from v$latch_misses where parent_name like 'cache buffers chains')
> This latch is taken more times than the consistent gets and db block
> gets combined.
> cache buffers lru chain latches is taken to manipulate buffers (or
> buffer headers) on the LRU chain. Normally the number os times these
> latches are acquired is almost equal to (or a bit more than) the
> Physical Reads.
>
> > What is meant by 'shared memory used by a cursor'? What is considered
> > shared?
> > I'm assuming that a parent cursor is the initial parse of the cursor. A
> > child cursor is created when a soft parse is done and new values are 'bound'
> > to the cursor. Am I correct?
> These 2 questions are related. The parse creates a parent cursor ( or
> loosely called that) which contains only the SQL_TEXT and some other
> info which is shared among all users. So if 2 users USERA and USERB
> have created table x and gave a query like this 'select * from x where
> a like 'AB%', there is only one parent cursor which contains this text
> 'select * from x where a like 'AB%'
> But each user is referring to his own object X so each will have his
> only context area (which you have called as a child cursor) which
> stores the context of the users like the object referenced (even
> non-existence of objects also !) and other information (like execution
> plan etc) which varies on execution. The parent is allocated in parse
> phase and the child during execute phase for each user. In the
> beginning of execute the child is allocated and for anything but
> selects it is freed at the end of execute. The total memory used by
> the parent and child is the Shared Memory shown in V$SQLAREA. There
> are actually 6 different sub heaps for each KGL object. If you want to
> see the memory used by each, you can query kglobhs0, kglobhs1,
> kglobhs2, kglobhs3, kglobhs4, kglobhs5, kglobhs6 from x$kglcursor
> where kglnaobj = <your query>.
> regards
> Srivenu
Received on Thu May 27 2004 - 09:34:01 CDT
