Re: Direct SGA access problem because of structs' changing start addresses (e.g., x$ksmsp)
- From: "keydana@xxxxxx" <keydana@xxxxxx>
- To: Tanel Poder <tanel@xxxxxxxxxxxxxx>
- Date: Mon, 13 Jan 2014 22:01:07 +0100
Hi Tanel,
thanks a lot, this is extremely helpful (and your advice on how to proceed is,
too :-)!
Looking forward very much to the next installments of the series!
Ciao
Sigrid
Am 10.01.2014 um 20:43 schrieb Tanel Poder:
> Not all X$ tables read their data directly from the source data structure.
> For some X$ tables a helper function is first executed, which then extracts
> th required data from wherever needed (by walking some linked list or even
> doing disk IO) and then copies the required data to your sessions UGA for
> presentation via the X$ fixed table interface. So you can't trust the
> addresses.
>
> I just wrote a blog entry to elaborate this and hopefully have time to write
> part 2 & 3 some day too:
>
> https://blog.tanelpoder.com/2014/01/10/oracle-x-tables-part-1-where-do-they-get-their-data-from/
>
> If you want to walk the shared pool structures, then I'd start from reading a
> bunch of shared pool heapdumps and Julian Dyke's shared pool presentation...
>
> --
> Tanel Poder
> Enkitec (The Exadata Experts)
> Services | Training | Troubleshooting | Exadata Book
>
>
>
> On Wed, Jan 8, 2014 at 12:33 AM, keydana@xxxxxx <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$ksuse...)
>
> It'd be great if anyone had advice, or an idea, what I could do to get this
> working all the same (and as to what the reason might be?)
> It ought to be possible somehow to do this, as I've tried oradebug direct
> access with x$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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