 | | | LOG FILE SYNC wait event | LOG FILE SYNC wait event 2007-09-05 - By DBA Deepak
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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@(protected)> 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@(protected)> 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
<div>Hi Alberto,</div>
<div> </div>
<div>Thanks a lot for your explanations. Have few more queries on ASMM
itself. Considering that we have set ASMM for our instance. </div>
<div> </div>
<div>> When more memory requered in a particular pool which pool Oracle does
choose to get the memory from?</div>
<div>> Is there any priorities associated?</div>
<div>> Why should we set the minimum values knowing that Oracle can adjust
them as and when required?</div>
<div> </div>
<div>Please help me in understanding the concepts.</div>
<div> </div>
<div>Thanks in Advance</div>
<div> </div>
<div>Deepak<br><br> </div>
<div><span class="gmail_quote">On 9/5/07, <b class="gmail_sendername">Alberto
Dell'Era</b> <<a href="mailto:alberto.dellera@(protected)">alberto.dellera
@(protected)</a>> wrote:</span>
<blockquote class="gmail_quote" style="PADDING-LEFT: 1ex; MARGIN: 0px 0px 0px 0
.8ex; BORDER-LEFT: #ccc 1px solid">From the Metalink note 373018.1 you suggested
, I get this important<br>fragment:<br>"Oracle combines fixed SGA area and
redo buffer together, if there is
<br>a free space after Oracle put combined buffer to fit in granule, that<br
>space is added to redo buffer"<br>so, the log_buffer initialization
parameter is not really "ignored",<br>but rather,<br>is used as a
minimum value - the log buffer size is that value plus
<br>(possibly) any additional free space in the granule(s) used to store<br>the
fixed SGA+log buffer.<br><br>So this explains nicely DBA Deepak's test case
.<br><br>But back to one of the the original questions - is the log buffer
<br>managed dynamically<br>by ASMM, that is, can its (real) size change after
instance boot time,<br>stealing memory<br>from other pools, or giving it back,
depending on the workload ?<br>If the documentation is consistent with the
actual behavior (and I
<br>always assume it is,<br>unless a convincing counterexample is presented),
no:<br><a href="http://download.oracle.com/docs/cd/B19306_01/server.102/b14237
/initparams192.htm">http://download.oracle.com/docs/cd/B19306_01/server.102
/b14237/initparams192.htm
</a><br><br>"SGA_TARGET specifies the total size of all SGA components. If
<br>SGA_TARGET is specified, then the following memory pools are<br
>automatically sized:<br><br> * Buffer cache (DB_CACHE
_SIZE)<br> * Shared pool (SHARED_POOL_SIZE)
<br> * Large pool (LARGE_POOL_SIZE)<br> *
Java pool (JAVA_POOL_SIZE)<br> * Streams
pool (STREAMS_POOL_SIZE)<br><br>If these automatically tuned memory pools are
set to non-zero values,<br>then those values are used as minimum levels by
Automatic Shared
<br>Memory Management. You would set minimum values if an application<br
>component needs a minimum amount of memory to function properly.<br><br>The
following pools are manually sized components and are not affected<br>by
Automatic Shared Memory Management:
<br><br> * Log buffer<br> * Other
buffer caches, such as KEEP, RECYCLE, and other block sizes<br> *
Fixed SGA and other internal allocations<br>"<br><br>So to
recap - the log buffer size may be greater then log_buffer, and may be
<br>increased to make "fixed sga size" + "log buffer size"
an exact multiple of<br>a granule. This calculation is made at instance boot
time; and the log buffer<br>size is constant after the the instance has booted.
<br><br>HTH<br>Alberto<br><br><br><br><br>On 9/4/07, Rich Jesse <<a href=
"mailto:rjoralist@(protected)">rjoralist@(protected)</a>>
wrote:<br>> If I'm not mistaken, log_buffer will be automagically sized
at instance
<br>> startup if using ASMM, effectively ignoring the setting of the log
_buffer<br>> parameter. This is eluded to in the paragraph below
your reference:<br>><br>> "The memory allocated to these pools
[including log_buffer] is deducted from
<br>> the total available for SGA_TARGET when Automatic Shared Memory
Management<br>> computes the values of the automatically tuned memory pools.
"<br>><br>> Also see MeatLink 373018.1.<br>><br>> Someone
please correct me if I'm wrong. (be gentle!)
<br>><br>> Rich<br>><br>> > BTW The log buffer is not managed by
the Automatic Shared Memory Management<br>> > in 10gR2:<br>> ><br>
> > <a href="http://download.oracle.com/docs/cd/B19306_01/server.102
/b14237/initparams192.htm">
http://download.oracle.com/docs/cd/B19306_01/server.102/b14237/initparams192
.htm</a><br>> ><br>> > "The following pools are manually sized
components and are not<br>> > affected by Automatic Shared Memory
Management:
<br>> > * Log buffer<br>><br>>
<br>><br><br><br>--<br>Alberto Dell'Era<br>"the more you know, the
faster you go"<br></blockquote></div><br><br clear="all"><br>-- <br
>Regards,<br><br>Deepak
<br>Oracle DBA
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