Re: how does oracle store cursors in memory?
- From: Scott <oraracdba@xxxxxxxxx>
- To: oracle-l@xxxxxxxxxxxxx
- Date: Fri, 13 Feb 2004 22:06:27 -0800 (PST)
I have a website. I just wouldn't think using Yahoo
would be so difficult to publish a simple character
based diagram.
Thanks,
Scott
--- Mladen Gogala <mgogala@xxxxxxxxxxxx> wrote:
> Scott, with all due respect, this diagram is very
> hard to
> understand, probably because of Yahoo. Do you have
> any website
> with the information like that? Is there any
> Metalink note?
> Can you post these papers elsewhere? I'm sure that
> people at
> www.miracleas.dk and www.hotsos.com would gladly
> publish your
> articles.
> Thanks, you are a great resource for this list.
>
> On 02/13/2004 11:57:25 PM, Scott wrote:
> > Ryan, I am attaching a better buffer cache diagram
> (I
> > hope). Except under certain full table scan
> conditions
> > Datablocks are not stored in the PGA. Everything
> is
> > done via the shared_pool and SGA through pointers.
> > If you select address from v$sqlarea this gives
> you
> > the handle address of the object in the library
> cache.
> > The theory is that if your application executes a
> sql
> > statement it should generate a hash and that
> address
> > may or may not already exists in the shared pool
> if it
> > does not then your process should generate an
> > execution plan and load the dictionary objects
> into
> > the ?dc? area of the shared pool and your PGA will
> now
> > have a pointer to that address. If the address
> already
> > exists then your pga will establish a pointer to
> the
> > already existing SQL (execution plans and other
> > necessities). Your PGA will also keep certain
> status
> > information about the status of the cursor as well
> as
> > pointers to sort segment handles. The bottom line
> is
> > that the PGA is usually a series of pointers to
> the
> > SGA.
> >
> > Without source code you have to make some
> assumptions
> > but you can figure a lot this out using the
> oradebug
> > command and the GNU debugger (gdb) to dump the
> > processes and use gdb to dig into the structures
> of
> > the PGA.
> >
> > Have fun. I remember when I like to do this kinda
> > stuff. Now I am just happy I can get Oracle to
> > install, run and not have any bugs.
> >
> > Scott
> >
> >
> > --- Ryan <ryan.gaffuri@xxxxxxx> wrote:
> > > I know that data blocks are stored in the sga in
> > > linked lists. When hash maps are created the
> data
> > > blocks are stored in the pga as part of the hash
> map
> > > in arrays/linked lists.
> > > How are cursors stored? Now the data for the
> cursors
> > > is going to be in the SGA. Is a cursor just a
> > > pointer to the memory location of the data in
> the
> > > SGA? Now I know a 'REF' cursor is basically a
> named
> > > pointer. Am I correct? What data structure does
> > > oracle use to store cursors?
> > >
> >
>
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> > > Please see the official ORACLE-L FAQ:
> > > http://www.orafaq.com
> > >
> >
>
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> >
> > __________________________________
> > Do you Yahoo!?
> > Yahoo! Finance: Get your refund fast by filing
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> >
> > -- HTML Attachment decoded to text by Ecartis --
> > -- File: Buffer Cache Overview.htm
> > -- Desc: Buffer Cache Overview.htm
> >
> > Buffer Cache Overview: ~~~~~~~~~~~~~~~~~~~~~~
> This example applies
> > to
> > Oracle7 and Oracle8, although in reality there may
> be multiple LRU
> > chains.
> > InOracle8i the LRU concept is replaced by a
> touch-count algorithm but
> > the
> > idea is the same. LRU Chain: Most Recent Doubly
> linked list Least
> > Recent
> > +------+------+------+ - - - -
> +------+------+------+------+------+ |
> > | | |
> > || PTR | | | | +------+------+------+ - - - -
> > +------+------+------+------+------+ Newly used
> buffers | We search
> > for are
> > placed at this end. | LRU just FREE buffers |
> points from this end
> > LRUW
> > Chain(Dirty List): | to of the LRU.
> +------+------+ - - +------+ |
> > buffer
> > Dirty buffers | | | | | | headers. are moved to
> +------+------+ - -
> > +------+
> > | LRUW if there (Cleared by DBWR) | is room. | |
> Hashing is | based
> > on
> > DBA |
> > modulo the | number of buckets. | A LATCH protects
> | each hash chain
> > |
> > |
> > ,-------.
>
--------------------------------/----------------------+
> > Double |
> > Hash |
>
<------------------------------/---------------------+
> |
> > linked
> > |
> > Bucket| ,--------. ,---------V----. ,--------. | |
> hash | 1 | ----->|
> > Buffer
> > |--->| Buffer |---->| Buffer |--+ | chain.
> `-------' <-----| Header
> > |<---|
> > Header |<----| Header |<---+ | 40 | | 2 | | 999 |
> | | | | | |
> > |--------| | |
> > | | |Usr|Wait| | | | | `--------' `--------------'
> `--------'
> > ,-------. | |
> > |: |SO. |--------------' | | | | | | `-------' | |
> Buffer Handle | |
> > state
> > object | | | | (actual DB blocks) | |
> ,-------------------. ,-------.
> > | | |
> > 1| | Hash | | | | | | Bucket| | |
> +-------------------+ | 2 | -->...
> > |
> > `---------->| 2 | `-------' <--... | | | |
> +-------------------+
> > | : :
> > |
> > +-------------------+ :
> `-------------------------->| 40 Data Block |
> > : | |
> > +-------------------+ : : +-------------------+
> ,-------. | 999 | |
> > Hash | |
> > | | Bucket| +-------------------+ | N | | 1000 |
> `-------' | | There
> > are a
> > PRIME +-------------------+ number of Hash
> buckets.
> >
> >
>
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