Re: Direct SGA access problem because of structs' changing start addresses (e.g., x$ksmsp)
- From: Frits Hoogland <frits.hoogland@xxxxxxxxx>
- To: keydana@xxxxxx
- Date: Tue, 7 Jan 2014 23:56:14 +0100
See inline.
Frits Hoogland
http://fritshoogland.wordpress.com
frits.hoogland@xxxxxxxxx
Phone: +31 20 8946342
On 07 Jan 2014, at 23:33, keydana@xxxxxx wrote:
> Hi,
>
> I'm trying to write some Haskell code for direct SGA access of - preferredly,
> as of today - x$ksmsp (sql queries against this table being expensive,
> possibly...), and for that I'm following the approach from Kyle Hailey, as
> detailed in the Oracle Wait Interface book.
>
> So I need the struct's start address, but unfortunately, when I query x$ksmsp
> several times in a row - even from the same sqlplus process - I get
> different results every time... (Actually, this seems to be the case with
> most fixed tables, apart from those "fixed" fixed ones as x$ksuse...)
This seems very logical to me. This view externalises the shared pool
administration (if memory serves me well), which has a lot of stuff going on
all the time.
You even might think twice about doing this on a real life, busy, system.
I would have to look it up, but I think this view holds latches to get a more
or less consistent view, which is the reason this view can take some time
(acquiring the latches).
The X$ views are essentially Oracle memory structures externalised as database
tables. Because the data is so transient (you are watching memory areas, hash
tables, arrays, etc. of a running program), the design of this views is the
tables can be inconsistent (it would hang your system to lock everything down
for a consistent version).
This means that even if you dump the shared pool of a running system a few
times from oradebug, you will see differences too, because all the processes
keep on doing stuff.
>
> It'd be great if anyone had advice, or an idea, what I could do to get this
> working all the same (and as to what the reason might be?)
Becasue the X$ tables are not tables, but externalised views on memory
structures of a running program.
> It ought to be possible somehow to do this, as I've tried oradebug direct
> access with x$ksmsp and it worked (of course, it runs in sqlplus, so I don't
> know...)
>
> Thanks a lot in advance!
>
> Sigrid--
> //www.freelists.org/webpage/oracle-l
>
>
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