ORA-4031 and Shared&nb…

ORA-4031 and Shared Pool Duration

Posted by Riyaj Shamsudeen on August
6, 2009

After reading my earlier post on shared pool
A stroll through shared pool heap , one of my client contacted
me with an interesting ORA-4031 issue. Client was getting ORA-4031
errors and shared pool size was over 4GB ( in a RAC environment).
Client DBA queried v$sgastat to show that there is plenty of free
memory in the shared pool. We researched the issue and it is worth
blogging. Client DBA was confused as to how there can be ORA-4031
errors when the shared pool free memory is few GBs.

Heapdump Analysis

At this point, it is imperative to take heapdump in level 2 and
Level 2 is for the shared pool heap dump. [ Please be warned that
it is not advisable to take shared pool heap dumps excessively, as
that itself can cause performance issue. During an offline
conversation, Tanel Poder said that heapdump can freeze instance as
his clients have experienced.]. This will create a trace file in
user_dump_dest destination and that trace file is quite useful in
analyzing the contents of shared pool heap. Tanel Poder has an excellent
script heapdump_analyzer
. I modified that script adding code for aggregation at hea, extent
and type levels to debug this issue further and it is available as
heapdump_dissect.ksh
. ( with a special permission from Tanel to publish this
script.)

Shared pool review

You can read much more about shared pool in my earlier blog
entry posted above. Just as a cursory review, shared pool is split
in to multiple sub heaps. In 10g, each of those sub heaps are
divided in to even smaller sub heaps, let’s call it mini-heaps. For
example, in this specific database, there are three sub heaps. Each
of those sub heaps are further split in to four mini-heaps (1,0),
(1,1), (1,2) and (1,3) each.

sga heap(1,0)
sga heap(1,1)
sga heap(1,2)
sga heap(1,3)

sga heap(2,0)
sga heap(2,1)
sga heap(2,2)
sga heap(2,3)

sga heap(3,0)
sga heap(3,1)
sga heap(3,2)
sga heap(3,3)

One or more extents are allocated to these mini-heaps
dynamically as these areas grow over the course of instance life
until there is no more free memory to allocate. In this blog entry,
let’s focus on the contents of these sub-heaps.

Following shows output of heapdump_dissect script at extent level
aggregation. As you can see sga heap (1,0) is allocated with 34
extents of 16M each. [ 16M comes from _ksmg_granule_size.]

Extent level summary
------------------
Sub heap          Extent             Type              Allocation cmt   Size
---------------- -----------------   ---------------   --------------  --------
sga heap(1,0)          EXTENT 0              free                   1792
sga heap(1,0)          EXTENT 0              perm   perm            15096064
sga heap(1,0)          EXTENT 0            R-free                   616
sga heap(1,0)          EXTENT 0            R-perm   perm            1678560
sga heap(1,0)          EXTENT 0        R-freeable   reserved stoppe 96
sga heap(1,0)          EXTENT 1              free                   808
sga heap(1,0)          EXTENT 1              perm   perm            15097048
sga heap(1,0)          EXTENT 1            R-free                   1248
sga heap(1,0)          EXTENT 1            R-perm   perm            1677928
sga heap(1,0)          EXTENT 1        R-freeable   reserved stoppe 96
sga heap(1,0)          EXTENT 2              free                   456
sga heap(1,0)          EXTENT 2              perm   perm            15097400
sga heap(1,0)          EXTENT 2            R-free                   1679176
sga heap(1,0)          EXTENT 2        R-freeable   reserved stoppe 96
...
sga heap(1,0)         EXTENT 34              free                   160
sga heap(1,0)         EXTENT 34              perm   perm            15097696
sga heap(1,0)         EXTENT 34            R-free                   1679176
sga heap(1,0)         EXTENT 34        R-freeable   reserved stoppe 96

Duration: A KGH policy

It gets interesting here. Notice that all “sga heap(1,0)” chunks
has allocation comment as “perm”. Allocation comment “perm” is
passed for permanent chunks. In a nutshell, all permanent chunks
are allocated from first mini-heap in each of these sub heaps i.e.
sga heap(1,0), sga heap(2,0) and sga heap(3,0) and so on. They are
only allocated in the first mini-heap and not in any other
mini-heap in these sub-heaps. Another example: PL/SQL DIANA type
chunks are allocated only in fourth mini-sub-heap (1,3) (2,3) and
(3,3) [in this instance].

sga heap(1,3)          freeable   PL/SQL DIANA    1318912
...
sga heap(2,3)          freeable   PL/SQL DIANA    1675296
...
sga heap(3,3)          freeable   PL/SQL DIANA    1458176

Point is that there is a new KGH policy based upon duration of a
chunk. All chunks are classified based upon their type ( or more
formally based upon the duration of that chunk) and the chunks with
the same duration is allocated from the same shared pool
mini-heaps. I think, this is a great idea, especially since only
few heaps of shared pool tend to be over worked and that should not
unnecessarily flush other parts of the sub-heap. Another important
thing to consider is that shared pool extents can be de-allocated
and allocated to other parts of SGA. For example, shared pool
extents can be deallocated from shared pool and allocated to buffer
cache to increase buffer cache size [ These reallocated chunks will
be marked with a comment KGH:NO ACCESS ]. By keeping the perm
chunks in the first mini-heap, extents can be deallocated quite
easily, without the need to move the perm chunks to different
areas.

So, What’s the problem?

Drawback is that these chunks are contained in that mini-heap.
For example, let’s say that chunks with permanent duration must be
allocated and there is no free space in the first mini-heap ( say
sga heap(1,0) ) and if a new extent can’t be added to that
mini-heap then ORA-4031 error is thrown even if there is plenty of
free space in some other mini-heap ( say sga heap(1,1), sga
heap(1,2) etc). So permanent chunks will be allocated only from sga
heap(N, 0) [ where N is sub-heap id 1, 2,3... ] and if that
mini-heap runs out of space, ORA-4031 will be thrown.

This is why client encountered ORA-4031 errors. Even though
there was plenty of free memory in other pools, simply permanent
chunks can not be allocated in the first mini-heap leading to
ORA-4031 errors. Of course, other chunks in that mini-heap can not
be deallocated either since those chunks are also permanent chunks.
Chances of these errors occurring in other sub-heaps such as sga
heap(N,1), sga heap(N,2) etc are less since recreatable/freeable
chunks can be flushed to accommodate incoming requests. Quick
resolution was to increase shared pool_size temporarily (until we
can reduce perm chunk usage due to another issue, which will be
resolved soon).

Parameter:_enable_shared_pool_durations

Above undocumented parameter controls this specific KGH policy
and default is true. [Note that setting an undocumented parameter
needs Oracle support blessing in a production database]. I tested
this in my test database setting parameter
_enable_shared_pool_durations=false and mini-heaps disappeared. If
this parameter is false, then duration of a chunk is not
considered. Following example shows that EXTENT 0 in sga heap(1,0)
contains non-perm allocations if this parameter is set to
FALSE.

EXTENT 0 addr=3CC00000
...
Chunk 3cfdf23c sz=     4096    freeable  "sql area       "  ds=3CFE4E0C
Chunk 3cfe023c sz=      540    recreate  "KQR PO         "  latch=41AE8FD4
...

Summary

In essence, duration enabled chunk allocation policy has been
introduced in 10g [ I don't know exact version]. This is usually
beneficial and ORA-4031 errors are possible even if there is plenty
of free space in other mini-heaps.

This can be read in pdf format from
Investigations:ORA-4031 and shared pool duration.

Also, there is a patent documents “duration based memory
management” available in the web (patent US 6,253,226). Those
documents provides in-depth analysis.

Update 1: Looks like these mini-heaps are formally called
duration from an Oracle internal resource. There are exactly 4
durations in each sub-heap and each duration has its own free list.
x$ksmsp.ksmchdur column indicates the duration of that chunk.

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This entry was posted on August 6, 2009 at
3:01 pm and is filed under Oracle database internals, Performance tuning, RAC. Tagged: durations, heapdump, KGH:NO ACCESS, ORA-4031, oracle performance, sga
heap, shared pool, shared pool heapdump, _enable_shared_pool_durations, _ksmg_granule_size. You can follow any responses to this
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14 Responses to “ORA-4031 and Shared
Pool Duration”

johnny
said

August
7, 2009 at 7:46 am
Hello. Thank you for this great info! Keep up the good job!

Reply

orainternals said

August
8, 2009 at 4:04 am
Thanks you for reading this blog.

Reply

Shared pool freelists (and durations) «
Oracle database internals by Riyaj said

August
9, 2009 at 8:36 pm
[...] before and it is applicable prior to Oracle version 9i. In
9i, sub-heaps were introduced. Further, shared pool durations were
introduced in Oracle version 10g. So, his script may not be
applicable from version 9i [...]

Reply

Martin
Decker said

August
12, 2009 at 7:23 am
Hi Riyaj,

could you give some information about the reason for the high
perm chunk usage?

Great analysis!

Martin

Reply

orainternals said

August
12, 2009 at 10:13 pm
Martin

Thanks for reading my blog.

“enqueue_resources” had sudden outburst of growth.

Client found an unfortunate code issue, that may have caused the
problem growth. Client has fixed that part of their code for now.
But, point is that this issue can happen in any instance and for a
completely different reason.

Cheers

Riyaj

Reply

Blogroll Report 31/07/2009 – 07/08/2009 «
Coskan’s Approach to Oracle said

August
12, 2009 at 2:33 pm
[...] Riyaj Shamsudeen- ORA-4031 and Shared Pool Duration
[...]

Reply

Hans-Peter Sloot
said

August
20, 2009 at 8:36 am
Hi Riyaj,

Could this behavior also lead to ORA-4030′s?

According to Dion Cho on http://dioncho.wordpress.com/2009/07/27/playing-with-ora-4030-error/

ORA-4030 can also occur because of pl/sql issues.

Regards

Hans-Peter

Reply

Hans-Peter Sloot
said

August
21, 2009 at 12:25 pm
Hi Riyaj,

You can skip my previous post.

I mixed up the sga and the pga.

I am currently investigating a problem with impdp which gives
ORA-04030′s at different stages of the import.

We have ORA-04030 with the (sort subheap,sort key) arguments.

The sort subheap part is full with about 1200 piece marked perm and
has only 6k left whereas it wants to allocte 64k. There is enough
free and freeable space in other subheaps though.

The other is ORA-04030 with (kxs-heap-c,kghsseg: qcstxsInit)

Don’t have a heap dump of it yet.

Do you have any advice.

Regards Hans-Peter

Reply

orainternals said

August
21, 2009 at 6:27 pm
Hi Hans-Peter

I thought, I replied to your comment, Sorry. Yep, ORA-4031 is for
shared pool heap and ORA-4030 is pga heap. Unless, shared server or
MTS is in use, they don’t mix up ( I think).

Some of the basic things you might want to check is :

1. Is this 32 bit software? Is your SGA+PGA exceeds 32 bit
boundaries?

2. Is there any limits check ulimit?

3. Is pga_target too small for the workload? any other underscore
parameters limiting? Anything in v$pgastat?

Of course, correct thing to do is errorstack and heapdump and
analyze those trace files.

Cheers

Riyaj

Reply

Hans-Peter Sloot
said

August
24, 2009 at 7:41 am
Hi Riyaj,

I should have mentioned. It is 64 bit AIX, the limits have been
checked again and again.

The total pga for this process is 358M and there is 6M free in
various heaps.

The sort subheap error comes while the impdp process is creating
the indexes.

I analyzed the heap dump of the sort subheap error.

Since I have no direct access I cannot check things myself
easily.

Hopefully the dba’s can generate the kxs-heap heapdump today.

Regards Hans-Peter

Reply

ORA-04030: out of process memory when
trying to allocate 840 bytes (kgsp-heap,kglss) « Gopi Desaboyina
Solaris Blogs said

December
4, 2009 at 3:27 am
[...] http://orainternals.wordpress.com/2009/08/06/ora-4031-and-shared-pool-duration/
[...]

Reply

love wife
& love life ——Roger » Blog Archive »
缓解ora-04031的一种方法 said

August
31, 2011 at 9:35 am
[...]
关于文中提到的脚本，大家可以去这里下载http://orainternals.wordpress.com/2009/08/06/ora-
4031-and-shared-pool-duration/ Posted in mangement, Oracle rdbms on
八月 31, 2011 [...]

Reply

Shared pool freelists (and durations) -
OraInternals said

January
1, 2012 at 12:29 am
[...] before and it is applicable prior to Oracle version 9i. In
9i, sub-heaps were introduced. Further, shared pool durations were
introduced in Oracle version 10g. So, his script may not be
applicable from version 9i [...]

Reply

eurohavuz said

August
14, 2012 at 3:31 am
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servis

Reply