what is the difference between a child cursor and a parent cursor?
>
> From: Riyaj Shamsudeen <rshamsud@(protected)>
> Date: 2004/03/31 Wed PM 12:15:42 EST
> To: oracle-l@(protected)
> Subject: RE: shared pool latch
>
> Let me try to keep this alive.. Responses in line..
> HTH
> Thanks
> Riyaj "Re-yas" Shamsudeen
> Certified Oracle DBA
>
> -----Original Message-----
> From: oracle-l-bounce@(protected)
> [mailto:oracle-l-bounce@(protected)
> Sent: Wednesday, March 31, 2004 4:21 AM
> To: oracle freelists.org
> Subject: shared pool latch
>
>
> Hi guys
> The following questions are confusing me,please could someone give
> explanation
> on the below
>
> 1)Is librarycache latch held during the whole process of parse,execute
> and fetch phases ,
> or it is held upto the time searching for the object in hash table and
> release.
>
> Library cache latch is held while searching for a parent cursor and
> subsequent child cursor with similar attributes with parent cursor
> pinned. Also library cache latch is held when creating a new library
> cache object if the child cursor is not_found or
> found_but_not_shareable. Since, parent cursor is pinned while searching
> for a child cursor, I am not sure whether the search for child cursor
> needs to hold on to the library cache latch or not. But if a new parent
> cursor is to be created then the library cache latch must be held.
>
> Execute and Fetch uses library cache pin and library cache locks to
> maintain the objects from undergoing concurrent modification.
>
> 2)session_cached_cursor caches the child cursor or parent cursors also.
> As far as I know, session_cached_cursor is searched for pinned child
> cursor. I don't know whether the parent is also kept in the session
> cached cursor or not.
>
> 3)While doing hard parse which latch is acquired ,shared pool or library
> cache latch or both,
> if it is both which latch will be acquired first?
>
> library cache latch is already held while requesting for shared pool
> latch. Shared pool latch is acquired to request/release space from the
> shared pool free memory area and released immediately after that.
> Request for library cache latch can never be made while holding the
> shared pool latch (at least up to 9i) as latch level semantics will
> prevent that ( as shared pool latch gets are always in willing-to-wait
> mode).
>
> Thanks in advance
> Syed
>
>
>
>
>
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-----Original Message-----
From: oracle-l-bounce@freelists.org [mailto:oracle-l-bounce@freelists.org] On Behalf Of Sultan Syed
Sent: Wednesday, March 31, 2004 4:21 AM
To: oracle freelists.org
Subject: shared pool latch

Hi guys
The following questions are confusing me,please could someone give explanation
on the below

 

1)Is librarycache latch held during the whole process of parse,execute and fetch phases ,
or it is held upto the time searching for the object in hash table and release. 

 

Library cache latch is held while searching for a parent cursor and subsequent child cursor with similar attributes with parent cursor pinned. Also library cache latch is held when creating a new library cache object if the child cursor is not_found or found_but_not_shareable. Since, parent cursor is pinned while searching for a child cursor, I am not sure whether the search for child cursor needs to hold on to the library cache latch or not. But if a new parent cursor is to be created then the library cache latch must be held.

 

Execute and Fetch uses library cache pin and library cache locks to maintain the objects from undergoing concurrent modification.

 

2)session_cached_cursor caches the child cursor or parent cursors also. 

As far as I know, session_cached_cursor is searched for pinned child cursor. I don't know whether the parent is also kept in the session cached cursor or not. 

 

3)While doing hard parse which latch is acquired ,shared pool or library cache latch or both,

if it is both which latch will be acquired first? 

 

library cache latch is already held while requesting for shared pool latch. Shared pool latch is acquired to request/release space from the shared pool free memory area and released immediately after that. Request for library cache latch can never be made while holding the shared pool latch (at least up to 9i) as latch level semantics will prevent that ( as shared pool latch gets are always in willing-to-wait mode).

 

Thanks in advance
Syed