Archive for September 2017

Super-Sizing PGA Workareas in Oracle 12c

After a customer asked me for possibilities of super-sizing PGA workareas in version 12c, I took the chance to revisit the topic and perform some tests. Great material has already been posted by Alex Fatkulin (Hotsos Symposium 2014) and Norbert Debes (Secrets of the Oracle Database, Apress), but I wanted to verify, how the current release is behaving and I found some interesting things.

Super-Sizing PGA Workareas in 12c


Cloud Control – Privilege Delegation – so you don´t have the oracle / root password?

Quite frequently in database environments, security policies dictate that only personalized logons to Unix / Linux are allowed and that from there, one has to “sudo” to change to the oracle account. While this adds an additional layer of security, it makes administration a little more complicated.

Oracle Enterprise Manager – Cloud Control has a feature, which allows to cope with such a sudo environment. The feature is called “Privilege Delegation”. This post describes how to set it up and for what it can be used.

  1. Setup of “sudo” by the root account
  2. In order to use privilege delegation, specific sudo rules have to be defined. This rule normally already exists:

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    mdecker ALL=(root) NOPASSWD:/bin/su - oracle

    In addition to this one, two additional rules are required. If only sudo to “oracle” is required, then only the first line is needed.

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    mdecker ALL=(oracle) SETENV:/u01/app/oracle/cloud/agent/sbin/nmosudo *
    mdecker ALL=(root) SETENV:/u01/app/oracle/cloud/agent/sbin/nmosudo *
  3. Setup of Privilege Delegation in Cloud Control
  4. Go to Setup -> Security -> Privilege Delegation.

    Then you can either set it globally via template or individually for each host. This depends mainly on the path to “sudo” binary in the operating system. Then you choose “sudo” and provide the path to the sudo binary on your operating system (bash$ which sudo). The required parameters are then appended: /usr/bin/sudo -E -u %RUNAS% %COMMAND%

  5. The next step is to configure a Named Credential.
  6. If you are in a team of administrators, then each administrator should have his own account to log on to Cloud Contol and avoid using “sysman” user. For obvious reasons, each administrator has to create his own “named credential” (Setup->Security->Named Credential), because it contains his personalized username and password.

    Here you provide your personalized credentials (username/password) and specify that sudo should be used to change to “oracle”.

  7. Lastly, verify that it works as desired.
  8. Go to “Targets” -> “Host” and click “Run Host Command”. Then give the command to run, e.g. “id -a”, and then add a named credential as well as a specific host and click “Run”.

    If all is well, then you will get this output showing you the id of user oracle.

How does this work behind the scenes? The agent java process spawns a process “nmo”. This process was granted SETUID root Privileges by executing $ORACLE_HOME/root.sh at the time of agent deployment. This executable is calling “sudo” to run command “nmosudo” as user oracle with the “payload” command, which the user wanted to execute.

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root   14595  3149  0 14:23 pts/0    00:00:00 /u01/app/oracle/cloud/agent/sbin/nmo
root   14598 14595  0 14:23 pts/1    00:00:00   /usr/bin/sudo -p ###AGENT-PDP-PASSWORD-PROMPT### -E -u oracle /u01/app/oracle/cloud/agent/sbin/nmosudo DEFAULT_PLUGIN DEFAULT_FUNCTIONALITY DEFAULT_SUBACTION DEFAULT_ACTION /bin/sh -c id -a
oracle 14602 14598  0 14:23 pts/1    00:00:00     sleep 300

The linux logfile /var/log/secure will contain this messages. It can be seen that the personal user “mdecker” was running the command “nmosudo” with the payload command “id -a” as attribute.

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Sep 13 22:03:59 xxx sudo:  mdecker : TTY=pts/2 ; PWD=/u01/app/oracle/cloud/agent/agent_inst/sysman/emd ; USER=oracle ; COMMAND=/u01/app/oracle/cloud/agent/sbin/nmosudo DEFAULT_PLUGIN DEFAULT_FUNCTIONALITY DEFAULT_SUBACTION DEFAULT_ACTION /bin/sh -c id -a


ORA-4031 Troubleshooting – Issue with durations in 11gR2

I recently had to troubleshoot an ORA-4031 issue at a client site. The issue reappeared 3 times within 2 months and only after escalating the SR to SEV1 and being quite persistent for an explanation, the second engineer attempting to solve the issue finally got it right.  Being curious, I digged into the trace files again to confirm and understand the issue here. This blog post describes the method to analyze the issue and how to troubleshoot.

  • First, when the issue first appears, it creates a 4031 trace file, which does not really give enough information to solve the problem. So I asked Oracle Support for specific trace events to properly diagnose it. The correctly mentioned event 10235 level 65536 and heapdump level 536870914  but required an instance restart. After explaining that this is not really possible and researching myself, I found these two events, which do not really need an instance restart. Event 10235 was not really necessary in this case, because the description of the allocations did not matter here.
ALTER system SET events '4031 trace name HEAPDUMP level 536870914, lifetime 1; name errorstack level 3, lifetime 1';
  • Now, after the issue appeared again, we finally had the relevant diagnostic information.

 

Allocation Request Summary Informaton
=====================================
Allocation request for: kglsim object batch
...
Heap: 0x6007b278, size: 3896
******************************************************
HEAP DUMP heap name="sga heap(3,0)"  desc=0x6007b278
extent sz=0xfe0 alt=248 het=32767 rec=9 flg=-126 opc=2
...
durations enabled for this heap
reserved granules for root 0 (granule size 134217728)
Total heap size    =2684352800. (2559 MB)
Total free space   =    38360
Total reserved free space   =120837856 (115MB) 
Permanent space    =2563474760
 
==============================================
TOP 10 MEMORY USES FOR SGA HEAP SUB POOL 1
----------------------------------------------
"free memory               "       6597 MB 71%
"gcs resources             "       1080 MB 12%
"gcs shadows               "        748 MB  8%
"db_block_hash_buckets     "        200 MB  2%
"kglsim object batch       "        189 MB  2%
"kglsim heap               "        112 MB  1%
"gcs res hash bucket       "         64 MB  1%
"ges big msg buffers       "         54 MB  1%
"dbktb: trace buffer       "         51 MB  1%
"KGLH0                     "         48 MB  1%
-----------------------------------------
free memory                        6597 MB
memory alloc.                      2747 MB
Sub total                          9344 MB
==============================================
TOP 10 MEMORY USES FOR SGA HEAP SUB POOL 2
----------------------------------------------
"free memory               "       6641 MB 70%
"gcs resources             "       1080 MB 11%
"gcs shadows               "        747 MB  8%
"db_block_hash_buckets     "        512 MB  5%
"gcs res hash bucket       "         64 MB  1%
"kglsim object batch       "         59 MB  1%
"dbktb: trace buffer       "         51 MB  1%
"KGLH0                     "         44 MB  0%
"kglsim heap               "         35 MB  0%
"ges enqueues              "         22 MB  0%
-----------------------------------------
free memory                        6641 MB
memory alloc.                      2831 MB
Sub total                          9472 MB
==============================================
TOP 10 MEMORY USES FOR SGA HEAP SUB POOL 3
----------------------------------------------
"free memory               "       6488 MB 71%
"gcs resources             "       1080 MB 12%
"gcs shadows               "        747 MB  8%
"db_block_hash_buckets     "        200 MB  2%
"kglsim object batch       "        105 MB  1%
"gc name table             "         72 MB  1%
"gcs res hash bucket       "         64 MB  1%
"kglsim heap               "         63 MB  1%
"dbktb: trace buffer       "         51 MB  1%
"KGLH0                     "         46 MB  1%
-----------------------------------------
free memory                        6488 MB
memory alloc.                      2600 MB
Sub total                          9088 MB
==============================================
TOP 10 MEMORY USES FOR SGA HEAP SUB POOL 4
----------------------------------------------
"free memory               "       6663 MB 70%
"gcs resources             "       1080 MB 11%
"gcs shadows               "        749 MB  8%
"db_block_hash_buckets     "        512 MB  5%
"kglsim object batch       "         59 MB  1%
"dbktb: trace buffer       "         51 MB  1%
"KGLH0                     "         47 MB  0%
"kglsim heap               "         35 MB  0%
"FileOpenBlock             "         35 MB  0%
"ges enqueues              "         22 MB  0%
-----------------------------------------
free memory                        6663 MB
memory alloc.                      2809 MB
Sub total                          9472 MB
TOTALS ---------------------------------------
Total free memory                    26 GB
Total memory alloc.                  11 GB
Grand total                          37 GB
  • This shows that 4031 was triggered for memory allocation request in sga heap (3,0) with size of 3896. This is smaller than 4400 bytes (_shared_pool_reserved_min_alloc), so the request can not be served the the shared pool reserved area.  Next, we can see that we have 4 subpools (kghdsidx_count) and each of them has around 6 GB of free memory. So, in total, we have 37 GB shared pool with 26 GB of it free, but one mini-subpool (duration 0) of subpool 3 still has run out of free contigous memory bigger than 3792 bytes.
  • Running Tanel´s heapdump_analyzer, I could verify that the largest chunk for sga heap(3,0) was indeed 3792 bytes and that all bigger chunks were allocated by “PERM” allocations.

 

 ./heapdump_analyzer  ./PROD1_ora_27396.trc > heap.txt
 
grep -e "---" -e "Total_size" -e "sga heap(3,0)"  heap.txt
 
-- Heapdump Analyzer v1.00 by Tanel Poder ( http://www.tanelpoder.com )
 
Total_size #Chunks  Chunk_size,        From_heap,       Chunk_type,  Alloc_reason
---------- ------- ------------ ----------------- ----------------- -----------------
 
114123720      17    6713160 ,    sga heap(3,0),           R-free,
28442152       1   28442152 ,    sga heap(3,0),             perm,  perm
...
7485000       1    7485000 ,    sga heap(3,0),             perm,  perm
6713080       1    6713080 ,    sga heap(3,0),           R-free,
6712104       1    6712104 ,    sga heap(3,0),           R-perm,  perm
...
3028568       1    3028568 ,    sga heap(3,0),             perm,  perm
...
 
8928       4       2232 ,    sga heap(3,0),             perm,  perm
7864       1       7864 ,    sga heap(3,0),             perm,  perm
5488       2       2744 ,    sga heap(3,0),             perm,  perm
3792       1       3792 ,    sga heap(3,0),             free,  <<<<<<<<<<<<<<
...

This shows that the first chunk of chunk_type “free” is of 3792 bytes, but request was for 3896 bytes. The
subpool (3,0) only has R-free (for shared_pool_reserved area) and PERM allocations of bigger size. The subpool (3,0) consists of 20 Extents á (128M Granule size). Each extent has

Researching the issue with “PERM” allocations brought me to:

ORA-4031: unable to allocate 4160 bytes of shared memory (“shared pool”,”unknown object”,”sga heap(4,0)”,”modification “) (Doc ID 1675470.1)

This note also confirms that the classification in 4 durations leads to a weak spot of duration 0 in any subpool for memory allocations due to high PERM utilization. The note mentions patch 8857940, which was also finally recommended by the support engineer.

HEAP DUMP heap name="sga heap(1,0)"  desc=0x600680e8
Total heap size    =2818570440
Total free space   =    28008 <<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<< 
Total reserved free space   =127549960
HEAP DUMP heap name="sga heap(1,1)"  desc=0x60069940
Total heap size    =805305840
Total free space   =632590232
Total reserved free space   = 40243520
HEAP DUMP heap name="sga heap(1,2)"  desc=0x6006b198
Total heap size    =1879046960
Total free space   =1734275840
Total reserved free space   = 93975928
HEAP DUMP heap name="sga heap(1,3)"  desc=0x6006c9f0
Total heap size    =4294964480
Total free space   =4072007248
Total reserved free space   =214821040
HEAP DUMP heap name="sga heap(2,0)"  desc=0x600719b0
Total heap size    =2952788080
Total free space   =    19144 <<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<
Total reserved free space   =147689440
HEAP DUMP heap name="sga heap(2,1)"  desc=0x60073208
Total heap size    =671088200
Total free space   =524561448
Total reserved free space   = 33565720
HEAP DUMP heap name="sga heap(2,2)"  desc=0x60074a60
Total heap size    =1879046960
Total free space   =1738701544
Total reserved free space   = 93984160
HEAP DUMP heap name="sga heap(2,3)"  desc=0x600762b8
Total heap size    =4429182120
Total free space   =4202264536
Total reserved free space   =221534200
HEAP DUMP heap name="sga heap(3,0)"  desc=0x6007b278
Total heap size    =2684352800
Total free space   =    38360 <<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<
Total reserved free space   =120837856
HEAP DUMP heap name="sga heap(3,1)"  desc=0x6007cad0
Total heap size    =671088200
Total free space   =526361840
Total reserved free space   = 33565720
HEAP DUMP heap name="sga heap(3,2)"  desc=0x6007e328
Total heap size    =1879046960
Total free space   =1736230384
Total reserved free space   = 93977784
HEAP DUMP heap name="sga heap(3,3)"  desc=0x6007fb80
Total heap size    =4294964480
Total free space   =4076323080
Total reserved free space   =214821040
HEAP DUMP heap name="sga heap(4,0)"  desc=0x60084b40
Total heap size    =2952788080
Total free space   =     8536 <<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<
Total reserved free space   =140977632
HEAP DUMP heap name="sga heap(4,2)"  desc=0x60087bf0
Total heap size    =1879046960
Total free space   =1735347144
Total reserved free space   = 93984160
HEAP DUMP heap name="sga heap(4,3)"  desc=0x60089448
Total heap size    =4429182120
Total free space   =4198496144
Total reserved free space   =221534200

For reference, these are the relevant parameters. Please note that all of these are set to default, except _kghdsidx_count which was reduced from 4 earlier and _ksmg_granule_size which was reduced to 128M.

NAME                                     VALUE
---------------------------------------- --------------------
__shared_pool_size                       38923141120
_dm_max_shared_pool_pct                  1
_enable_shared_pool_durations            TRUE
_io_shared_pool_size                     4194304
_kghdsidx_count                          4
_ksmg_granule_size                       134217728
_memory_imm_mode_without_autosga         TRUE
_shared_pool_max_size                    0
_shared_pool_minsize_on                  FALSE
_shared_pool_reserved_min_alloc          4400
_shared_pool_reserved_pct                5
shared_pool_reserved_size                1946157056
shared_pool_size                         38654705664

Thanks to Tanel, Riyaj and Hatem Mahmoud