Re: LOG FILE SYNC wait event

Hi Alberto,

Thanks a lot for your explanations. Have few more queries on ASMM itself. Considering that we have set ASMM for our instance.

> When more memory requered in a particular pool which pool Oracle does
choose to get the memory from?
> Is there any priorities associated?
> Why should we set the minimum values knowing that Oracle can adjust them
as and when required?

Please help me in understanding the concepts.

Thanks in Advance

Deepak

On 9/5/07, Alberto Dell'Era <alberto.dellera_at_gmail.com> wrote:
>
> From the Metalink note 373018.1 you suggested, I get this important
> fragment:
> "Oracle combines fixed SGA area and redo buffer together, if there is
> a free space after Oracle put combined buffer to fit in granule, that
> space is added to redo buffer"
> so, the log_buffer initialization parameter is not really "ignored",
> but rather,
> is used as a minimum value - the log buffer size is that value plus
> (possibly) any additional free space in the granule(s) used to store
> the fixed SGA+log buffer.
>
> So this explains nicely DBA Deepak's test case.
>
> But back to one of the the original questions - is the log buffer
> managed dynamically
> by ASMM, that is, can its (real) size change after instance boot time,
> stealing memory
> from other pools, or giving it back, depending on the workload ?
> If the documentation is consistent with the actual behavior (and I
> always assume it is,
> unless a convincing counterexample is presented), no:
>
> http://download.oracle.com/docs/cd/B19306_01/server.102/b14237/initparams192.htm
>
> "SGA_TARGET specifies the total size of all SGA components. If
> SGA_TARGET is specified, then the following memory pools are
> automatically sized:
>
> * Buffer cache (DB_CACHE_SIZE)
> * Shared pool (SHARED_POOL_SIZE)
> * Large pool (LARGE_POOL_SIZE)
> * Java pool (JAVA_POOL_SIZE)
> * Streams pool (STREAMS_POOL_SIZE)
>
> If these automatically tuned memory pools are set to non-zero values,
> then those values are used as minimum levels by Automatic Shared
> Memory Management. You would set minimum values if an application
> component needs a minimum amount of memory to function properly.
>
> The following pools are manually sized components and are not affected
> by Automatic Shared Memory Management:
>
> * Log buffer
> * Other buffer caches, such as KEEP, RECYCLE, and other block sizes
> * Fixed SGA and other internal allocations
> "
>
> So to recap - the log buffer size may be greater then log_buffer, and may
> be
> increased to make "fixed sga size" + "log buffer size" an exact multiple
> of
> a granule. This calculation is made at instance boot time; and the log
> buffer
> size is constant after the the instance has booted.
>
> HTH
> Alberto
>
>
>
>
> On 9/4/07, Rich Jesse <rjoralist_at_society.servebeer.com> wrote:
> > If I'm not mistaken, log_buffer will be automagically sized at instance
> > startup if using ASMM, effectively ignoring the setting of the
> log_buffer
> > parameter. This is eluded to in the paragraph below your reference:
> >
> > "The memory allocated to these pools [including log_buffer] is deducted
> from
> > the total available for SGA_TARGET when Automatic Shared Memory
> Management
> > computes the values of the automatically tuned memory pools."
> >
> > Also see MeatLink 373018.1.
> >
> > Someone please correct me if I'm wrong. (be gentle!)
> >
> > Rich
> >
> > > BTW The log buffer is not managed by the Automatic Shared Memory
> Management
> > > in 10gR2:
> > >
> > >
> http://download.oracle.com/docs/cd/B19306_01/server.102/b14237/initparams192.htm
> > >
> > > "The following pools are manually sized components and are not
> > > affected by Automatic Shared Memory Management:
> > > * Log buffer
> >
> >
> >
>
>
> --
> Alberto Dell'Era
> "the more you know, the faster you go"
>

-- 
Regards,

Deepak
Oracle DBA

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