Donnerstag, 16. November 2017

Backup stalled due to ASM rebalance stuck

I hit an issue where a full backup took much longer than normal.
In this case there was no alarm yet as no threshold was reached. But I worked on the DB for some other reason and out of a habit I most often start a ASH viewer whenever I work on a system - even if I only check data, it's worth to have an eye on the system.
In this case I saw some top session in waits 'ASM file metadata operation' & 'KSV master wait'.
It wasn't my query session (so I didn't break anything) but some RMAN worker processes.

That's worth to investigate. After some research (Google & MetaLink) I saw some links between ASM rebalance and 'ASM file metadata operation'.

Checking the ASM instance, there was really a ASM rebalance ongoing, but no progress (no change in v$asm_operation.SOFAR over some minutes). It was initiated the other evening by a colleague which added a disk to the DG. I agree with Kevin this is a bad habit, but in this environment it's not enough pain (and multiple teams involved) to re-work all the processes. The RBAL process was waiting in 'enq: RB - contention'.

As ASM rebalance can be stopped or re-started wit othe rpriority easily, I gave this a chance and run ALTER DISKGROUP dg REBALANCE POWER 2 - the power is not important here, ony to stop the current (stalled) rebalance and issue another.

The ASH viewer immediately showed the uncommon waits disappear and in RMAN logs I saw ordinary progress immediately.

To be honest I did not much analysis here, so it might be worth to do better, but in this case it was sufficient and the issue solved even before there was an alarm regarding the blocked backup.

Once again, ASH (and my curiosity) helped solving the issue. 

Donnerstag, 26. Oktober 2017

prelink makes instance unusable

I spent a recent night hunting an issue which was non trivial to detect.
On a 4 node cluster 2 nodes got Linux patches and were rebooted. This was done after 10pm for minimal business impact. (The application is written by Oracle - so it's not fully TAF aware).
The DBs started fine, all services were available.
At 3:50 in the morning I got a call some processes show strange errors.
As I connected to the Server, the Instance shows running proceses. But I could not connect to the instance:
With proper environment variables, the errors were:
sqlplus system/xxx

SQL*Plus: Release 11.2.0.4.0 Production on Thu Oct 19 03:58:52 2017

Copyright (c) 1982, 2013, Oracle.  All rights reserved.

Enter password:
ERROR:
ORA-01034: ORACLE not available
ORA-27123: unable to attach to shared memory segment
Linux-x86_64 Error: 22: Invalid argument
Additional information: 25
Additional information: 323780623
Additional information: -1610612736
Process ID: 0
Session ID: 0 Serial number: 0

Enter user-name:
ERROR:
ORA-01017: invalid username/password; logon denied

and

sqlplus system/xxx

SQL*Plus: Release 11.2.0.4.0 Production on Thu Oct 19 03:59:33 2017

Copyright (c) 1982, 2013, Oracle.  All rights reserved.

Connected to an idle instance.

SQL> 

So it seems it's related to shared memory.


First checks showed there are enough hugepages configured and available, ipcs lists them correct.

in alert.log I found entries like
Thu Oct 19 03:34:41 2017
Process q003 died, see its trace file
Thu Oct 19 03:35:40 2017
Process W000 died, see its trace file
Process W000 died, see its trace file
Process W000 died, see its trace file
Thu Oct 19 03:35:52 2017
Process W000 died, see its trace file
Process W000 died, see its trace file
Thu Oct 19 03:35:57 2017
Process m000 died, see its trace file
Process W000 died, see its trace file
Thu Oct 19 03:36:04 2017
and
Thu Oct 19 04:00:02 2017
Process J000 died, see its trace file
kkjcre1p: unable to spawn jobq slave process
Errors in file /...diag.../trace/INST_NAME_cjq0_61788.trc:
Process W000 died, see its trace file
Thu Oct 19 04:00:04 2017

this contains
*** 2017-10-19 04:00:02.536
*** SESSION ID:(631.21) 2017-10-19 04:00:02.536
*** CLIENT ID:() 2017-10-19 04:00:02.536
*** SERVICE NAME:(SYS$BACKGROUND) 2017-10-19 04:00:02.536
*** MODULE NAME:() 2017-10-19 04:00:02.536
*** ACTION NAME:() 2017-10-19 04:00:02.536

Process J000 is dead (pid=119122 req_ver=453 cur_ver=453 state=KSOSP_SPAWNED).

*** 2017-10-19 04:00:09.545
Process J000 is dead (pid=119264 req_ver=456 cur_ver=456 state=KSOSP_SPAWNED).

*** 2017-10-19 04:00:12.539
Process J000 is dead (pid=119278 req_ver=25 cur_ver=25 state=KSOSP_SPAWNED).

With all this information (and some search effort) the best match I found is Connected to an idle instance, while database instance is running (Process J000 died, see its trace file kkjcre1p: unable to spawn jobq slave process ) (Doc ID 1578491.1).

But why is prelink doing such bad things?


Some information about the memory structure of the running instance and new started process, together with a good old strace will shed some light:

first of all the /proc/<pid>/maps content of the running smon (any process attached to the instance would do):
00400000-0bdbb000 r-xp 00000000 fd:ac 4730278                            /O_H/bin/oracle
0bfba000-0c1b4000 rw-p 0b9ba000 fd:ac 4730278                            /O_H/bin/oracle
0c1b4000-0c20b000 rw-p 00000000 00:00 0
0c89b000-0c8fe000 rw-p 00000000 00:00 0                                  [heap]
60000000-a0000000 rw-s 00000000 00:0c 323747854                          /SYSV00000000 (deleted)
a0000000-3260000000 rw-s 00000000 00:0c 323780623                        /SYSV00000000 (deleted)
3260000000-3260200000 rw-s 00000000 00:0c 323813392                      /SYSV6a4ae364 (deleted)
3c2ee00000-3c2ee01000 r-xp 00000000 fd:01 1625                           /lib64/libaio.so.1.0.1
3c2ee01000-3c2f000000 ---p 00001000 fd:01 1625                           /lib64/libaio.so.1.0.1
3c2f000000-3c2f001000 rw-p 00000000 fd:01 1625                           /lib64/libaio.so.1.0.1
7feb42051000-7feb42061000 rw-p 00000000 00:05 4603                       /dev/zero
7feb42061000-7feb42071000 rw-p 00000000 00:05 4603                       /dev/zero
7feb42071000-7feb42081000 rw-p 00000000 00:05 4603                       /dev/zero
7feb42081000-7feb42091000 rw-p 00000000 00:05 4603                       /dev/zero
7feb42091000-7feb420a1000 rw-p 00000000 00:05 4603                       /dev/zero
...
7feb42750000-7feb42751000 rw-p 0007f000 00:05 4603                       /dev/zero
7feb42751000-7feb42891000 rw-p 00000000 00:00 0
7feb42891000-7feb4289d000 r-xp 00000000 fd:01 3650                       /lib64/libnss_files-2.12.so
7feb4289d000-7feb42a9c000 ---p 0000c000 fd:01 3650                       /lib64/libnss_files-2.12.so
7feb42a9c000-7feb42a9d000 r--p 0000b000 fd:01 3650                       /lib64/libnss_files-2.12.so
7feb42a9d000-7feb42a9e000 rw-p 0000c000 fd:01 3650                       /lib64/libnss_files-2.12.so
7feb42a9e000-7feb42b9e000 rw-p 00000000 00:00 0
7feb42b9e000-7feb42ba8000 r-xp 00000000 fd:a4 2880                       /usr/lib64/libnuma.so.1 (deleted)
7feb42ba8000-7feb42da8000 ---p 0000a000 fd:a4 2880                       /usr/lib64/libnuma.so.1 (deleted)
7feb42da8000-7feb42da9000 rw-p 0000a000 fd:a4 2880                       /usr/lib64/libnuma.so.1 (deleted)
7feb42da9000-7feb42f33000 r-xp 00000000 fd:01 118                        /lib64/libc-2.12.so (deleted)
7feb42f33000-7feb43133000 ---p 0018a000 fd:01 118                        /lib64/libc-2.12.so (deleted)
7feb43133000-7feb43137000 r--p 0018a000 fd:01 118                        /lib64/libc-2.12.so (deleted)
7feb43137000-7feb43139000 rw-p 0018e000 fd:01 118                        /lib64/libc-2.12.so (deleted)
7feb43139000-7feb4313d000 rw-p 00000000 00:00 0
7feb4313d000-7feb43153000 r-xp 00000000 fd:01 3646                       /lib64/libnsl-2.12.so (deleted)
7feb43153000-7feb43352000 ---p 00016000 fd:01 3646                       /lib64/libnsl-2.12.so (deleted)
7feb43352000-7feb43353000 r--p 00015000 fd:01 3646                       /lib64/libnsl-2.12.so (deleted)
7feb43353000-7feb43354000 rw-p 00016000 fd:01 3646                       /lib64/libnsl-2.12.so (deleted)
7feb43354000-7feb43356000 rw-p 00000000 00:00 0
7feb43356000-7feb4336d000 r-xp 00000000 fd:01 142                        /lib64/libpthread-2.12.so.#prelink#.O7kB09 (deleted)
7feb4336d000-7feb4356d000 ---p 00017000 fd:01 142                        /lib64/libpthread-2.12.so.#prelink#.O7kB09 (deleted)
7feb4356d000-7feb4356e000 r--p 00017000 fd:01 142                        /lib64/libpthread-2.12.so.#prelink#.O7kB09 (deleted)
7feb4356e000-7feb4356f000 rw-p 00018000 fd:01 142                        /lib64/libpthread-2.12.so.#prelink#.O7kB09 (deleted)
7feb4356f000-7feb43573000 rw-p 00000000 00:00 0
7feb43573000-7feb435f6000 r-xp 00000000 fd:01 3644                       /lib64/libm-2.12.so (deleted)
7feb435f6000-7feb437f5000 ---p 00083000 fd:01 3644                       /lib64/libm-2.12.so (deleted)
7feb437f5000-7feb437f6000 r--p 00082000 fd:01 3644                       /lib64/libm-2.12.so (deleted)
7feb437f6000-7feb437f7000 rw-p 00083000 fd:01 3644                       /lib64/libm-2.12.so (deleted)
7feb437f7000-7feb437f9000 r-xp 00000000 fd:01 3642                       /lib64/libdl-2.12.so (deleted)
7feb437f9000-7feb439f9000 ---p 00002000 fd:01 3642                       /lib64/libdl-2.12.so (deleted)
7feb439f9000-7feb439fa000 r--p 00002000 fd:01 3642                       /lib64/libdl-2.12.so (deleted)
7feb439fa000-7feb439fb000 rw-p 00003000 fd:01 3642                       /lib64/libdl-2.12.so (deleted)
7feb439fb000-7feb43a07000 r-xp 00000000 fd:ac 4593158                    /O_H/lib/libocrutl11.so
7feb43a07000-7feb43b06000 ---p 0000c000 fd:ac 4593158                    /O_H/lib/libocrutl11.so
...
Here we see at the top 3 shared memory segments (bold) - the one with id 323780623 will be of special interest.

As I try to attach a new process (sqlplus) to the instance, strace shows me
...
9134  shmat(323780623, 0xa0000000, 0)   = -1 EINVAL (Invalid argument)
9134  shmctl(323780623, IPC_STAT, 0x7fffc48703c8) = 0
9134  shmat(323780623, 0, 0)            = 0x2aaaaac00000
9134  shmdt(0x2aaaaac00000)             = 0
9134  uname({sys="Linux", node="av3l291p", ...}) = 0
9134  times({tms_utime=0, tms_stime=1, tms_cutime=0, tms_cstime=0}) = 432291212
9134  times({tms_utime=0, tms_stime=1, tms_cutime=0, tms_cstime=0}) = 432291212
9134  stat("/O_H/rdbms/log", {st_mode=S_IFDIR|0755, st_size=503808, ...}) = 0
9134  stat("/O_H/rdbms/log/ebssip021_ora_9134.trc", 0x7fffc486c810) = -1 ENOENT (No such file or directory)
9134  open("/O_H/rdbms/log/ebssip021_ora_9134.trc", O_WRONLY|O_CREAT|O_TRUNC, 0660) = 4
9134  lstat("/O_H/rdbms/log/ebssip021_ora_9134.trc", {st_mode=S_IFREG|0640, st_size=0, ...}) = 0
...
Its a nice habit to write a trace file in such a situation.  Oracle Trace Files are often great. In this case, it contains (beside many other things) information about the shared memory segments:
*********************** Dumping ipcs output ********************
------ Shared Memory Segments --------
key        shmid      owner      perms      bytes      nattch     status
0x00000000 260440066  oracle     600        4096       0
0x00000000 260472835  oracle     600        4096       0
0x2bac4398 260505604  oracle     600        24576      95
0x00000000 320405509  oracle     640        67108864   85
0x00000000 320438278  oracle     640        10670309376 85
0xa6f47cf8 320471047  oracle     640        2097152    85
0x00000000 323485704  oracle     640        33554432   94
0x00000000 323551241  oracle     640        16777216   146
0x00000000 323584010  oracle     640        1056964608 146
0x8015f33c 323616779  oracle     640        2097152    146
0x00000000 323649548  oracle     640        2113929216 94
0xb047bb08 323682317  oracle     640        2097152    94
0x00000000 323747854  oracle     640        1073741824 76
0x00000000 323780623  oracle     640        213674622976 75
0x6a4ae364 323813392  oracle     640        2097152    76
0x00000000 326828049  oracle     640        50331648   128
0x00000000 326860818  oracle     640        5318377472 128
0x3df7a980 326893587  oracle     640        2097152    128

and the process map:
******************* Dumping process map ****************
00400000-0bdbb000 r-xp 00000000 fd:ac 4730278                            /O_H/bin/oracle
0bfba000-0c1b4000 rw-p 0b9ba000 fd:ac 4730278                            /O_H/bin/oracle
0c1b4000-0c20b000 rw-p 00000000 00:00 0
0d2c4000-0d309000 rw-p 00000000 00:00 0                                  [heap]
60000000-a0000000 rw-s 00000000 00:0c 323747854                          /SYSV00000000 (deleted)
324e000000-324e020000 r-xp 00000000 fd:01 119                            /lib64/ld-2.12.so
324e220000-324e221000 r--p 00020000 fd:01 119                            /lib64/ld-2.12.so
324e221000-324e222000 rw-p 00021000 fd:01 119                            /lib64/ld-2.12.so
324e222000-324e223000 rw-p 00000000 00:00 0
324e400000-324e58a000 r-xp 00000000 fd:01 120                            /lib64/libc-2.12.so
324e58a000-324e78a000 ---p 0018a000 fd:01 120                            /lib64/libc-2.12.so
324e78a000-324e78e000 r--p 0018a000 fd:01 120                            /lib64/libc-2.12.so
324e78e000-324e790000 rw-p 0018e000 fd:01 120                            /lib64/libc-2.12.so

My sqlplus process tried to attach the shared memory segment 323780623 at address 0xa0000000 ( shmat(323780623, 0xa0000000, 0) ) but it failed (-1 EINVAL).
The reason for the failure is the alredy linked library /lib64/ld-2.12.so at address 324e000000 (and some others as well).

But why is it so important to have this shared memory at the specific address? As strace shows, it was able to map it on some other address without any issue ( shmat(323780623, 0, 0  = 0x2aaaaac00000 ).

But Oracle requires the shared memory segments mapped at the same address for all processes of an instance. It uses the direct memory address to access all it's memory structures. E.g. when querying saddr or paddr from v$session, these are the real addresses.
So if you map a shared memory process with your own binary at the same address, you can access the memory structures direct using these addresses.

So what bad did prelink make to the system?


The Linux server was patched at about midnight. A lot of new RPMs were installed and the server rebooted. Clusterware started and fine and int started all instances.
But sometime close to 03:34 prelink was started, it did a lot of work with all the new libraries and created a new /etc/prelink.cache file, so all new started binaries loads their libraries according to this file. In my case the shared memory segment could not be loaded at the specific address anymore - so the Instance was still healthy, but no new process could attach anymore.

My solution was to kill the instance and restart it.
Generally I recommend to disable prelink on Linux hosts running Oracle database.

Oracle also recommends doing so.

Freitag, 20. Oktober 2017

Oracle Bundle Patches - release timing

I have to invest much of my time (at work) into Oracle and managing of patches, merge patches, patch requests and similar things.
At this task I identified an interesting (but probably worthless) information:
It seems a Bundle Patch (for Version 12.1) is defined approximately (at least) 40 days before it's released.
At least the 12.1.0.1.171017 BP follows this rule.

I have requested a lot of one-off and merge patches on top of 12.1.0.2.171017BP over the last days. In the picture you can see 2 requests with date of 18th and 20th Oct. Others with Requested "Not Specified" are delivered already.
But there are some in the list with 7th and 8th of September. As my "Associated Request" ID is increasingit's shown I requested them in order (and without time machine) - all of them were requests based on Database Proactive Bundle Patch 12.1.0.2.171017 Patch 26635880 which was nit GA before 10th of October.
So a valid conclusion is: The content of Patch 26635880 was defined before 7th of September.
At about 7th and 8th September many merge request were raised internally - by whatever mechanism they were chosen.
Many of them were available when Patch 26635880 was available - others still pending. (Maybe they wait for more customers to request - like a kind of vote - but that's pure guessing).
Is this information of any value?
At a first sign no. As a customer still we don't know which patches will be fixed in an upcoming BundlePatch/RCU.
But if we are really demanding, we can start approx. 40 days early to force Support / Presales / Account Manager to make sure a patch for a given bug is available within next PSU/RCU.

So, if it's really urgent, don't wait until mid of January 2018 - start in early December to request your merge patches on top of  12.1.0.2.18.01.16 (or 12.2 ...)

Montag, 25. September 2017

digging into mrskew internals

I'm spending some time working with Method-Rs trace file analyzer mrskew.
As the requirements are beyond simple analyses (here an example about the uncommon things to do) I'm consulting the documentation and all available information in detail. After many readings I started to take this part of the documentation serious:

EXPRESSIONS
Wherever mrskew requires an expression (such as in --group and --where option arguments), you may use any valid Perl expression consisting of:
Perl operators
Operators such as or xor and not , = ?: || && | ^ < > <= >= lt gt le ge == != <=> eq ne cmp + - . * / % =~ !~ ! ~ ** ...and so on. See http://perldoc.perl.org/perlop.html for details.
Perl builtin functions
Functions such as lc uc s/// int join split sprintf substr ...and so on. See http://perldoc.perl.org/perlfunc.html for details.
File::Basename functions
The functions fileparse, basename, and dirname. See http://perldoc.perl.org/File/Basename.html for details.
mrskew expression variables
Any of the variable names described in "EXPRESSION VARIABLES".
For more information about Perl expression syntax, see http://perldoc.perl.org/perl.html#Tutorials.

It's written "any valid Perl expression" and Jeff showed me a very clever example on StackOverflow. But that's not the end, it raised some questions:
Where in the work of mrskew is the specific expression executed?
What's the order of these expressions?
Can they interact?

A small testcase can answer some of these questions.

I used a very simple artificial tracefile:
Oracle Release 11.2
PARSING IN CURSOR #1 len=20 dep=0 uid=7 oct=6 lid=7 tim=2 hv=1 ad='1' sqlid='A'
insert
END OF STMT

EXEC #1:c=1,e=1,p=0,cr=0,cu=0,mis=0,r=0,dep=0,og=3,tim=100
EXEC #1:c=2,e=4,p=0,cr=0,cu=0,mis=0,r=0,dep=0,og=6,tim=400

a small rc file (rc file is used here to store parameters whenever it's boring to type them on command line):
--init='
 my $trace_string = "trace: ";
 my $test_string;
    sub xfrm {
   if ($_[0] eq "where0") {
     $test_string = $test_string . "x";}
   if ($_[0] eq "where1") {
     $test_string =~ s/x/u/g ;}  
      $trace_string = $trace_string . "$_[0]" . "{ $test_string } " . "[$line] -> ";
   
   if ($_[0] eq "group") {
     return $trace_string;}
  else {
    return $_[1]}
    }
'

this uses the --init parameter:
--init=stringExecute string, which must contain syntactically correct Perl code, before beginning file processing. The default value is --init=''.
There I'm setting 2 variables which will be used later.
Also a function xfrm is defined. Depending of the 1st parameter it does different things, always it extends the variable $trace_string with some additional parameters. When the 1st parameter is "group", this $trace_string is returned - my dirty hack for a print of a debug value.

Checking the manpage where an expression ls allowed for a parameter gives me this execution:
(slightly modified for better readability

mrskew --rc martin3.rc  \
  --select='xfrm( "select", 1)' \
  --where0='xfrm( "where0", 1)==1' \
  --where1='xfrm( "where1", 1)==1' \
  --group='xfrm( "group",1)' \
  berx2.trc

The idea is simple: wherever a expression is allowed, my generic function xfrm is called with the name of the mrskew-parameter as it's 1st parameter.

It's result provides some interesting insights:
Summary information by file (modified)
mrskew --rc martin3.rc  --select='xfrm( "select", 1)' --where0='xfrm( "where0", 1)==1' --where1='xfrm( "where1", 1)==1' --group='xfrm( "group",1)' berx2.trc "D:\TEMP\berx2.trc"
Run began 2017-09-25T09:54:40, lasted 0,445000 seconds

input files:
 'D:\TEMP\berx2.trc'

where expression:
 ((xfrm( "where0", 1)==1) and (xfrm( "where1", 1)==1)) and ($nam=~/(?^:(?i).+)/)

group expression:
 xfrm( "group",1)

matched call names:
 'EXEC'

'xfrm( "group",1)'                                                                                                                                                                                                                                                                                                 'xfrm( "select", 1)'       %  CALLS      MEAN       MIN       MAX
-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------  --------------------  ------  -----  --------  --------  --------
trace: where0{ x } [1] -> where1{ u } [1] -> where0{ ux } [4] -> where1{ uu } [4] -> where0{ uux } [5] -> where1{ uuu } [5] -> where0{ uuux } [6] -> where1{ uuuu } [6] -> select{ uuuu } [6] -> group{ uuuu } [6] ->                                                                                                          1.000000   50.0%      1  1.000000  1.000000  1.000000
trace: where0{ x } [1] -> where1{ u } [1] -> where0{ ux } [4] -> where1{ uu } [4] -> where0{ uux } [5] -> where1{ uuu } [5] -> where0{ uuux } [6] -> where1{ uuuu } [6] -> select{ uuuu } [6] -> group{ uuuu } [6] -> where0{ uuuux } [7] -> where1{ uuuuu } [7] -> select{ uuuuu } [7] -> group{ uuuuu } [7] ->               1.000000   50.0%      1  1.000000  1.000000  1.000000
-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------  --------------------  ------  -----  --------  --------  --------
TOTAL (2)                                                                                                                                                                                                                                                                                                                      2.000000  100.0%      2  1.000000  1.000000  1.000000
mrskew: file 'berx2.trc' does not exist

As the $trace_string is quite long I cut it down into pieces and my interpretation:
trace: where0{ x } [1] -> where1{ u } [1] -> 
where0 is called before where1
where1 can modify a variable set by where0 (the x becomes an u).

where0{ ux } [4] -> where1{ uu } [4] -> where0{ uux } [5] -> where1{ uuu } [5] -> 
where0 and where1 are NOT used in lines 2 & 3 of the trace file (PARSING IN CURSOR and the insert statement)

where0{ uuux } [6] -> where1{ uuuu } [6] -> select{ uuuu } [6] -> group{ uuuu } [6] -> 

in line 6 (EXEC) where0, where1, select and group functions are used (in that order)

where0{ uuuux } [7] -> where1{ uuuuu } [7] -> select{ uuuuu } [7] -> group{ uuuuu } [7] ->

the same is true for line 7.

There is probably more to identify as my simplified tracefile did not show all possible lines and their combination. But the possibility to run code inside mrskew at different positions, and even manipulate some values is shown. Even manipulating mrskews own variables might be of some interest, but it must be identified first where/when they are set and changed. This is open for the readers exercise, the method is shown here :-)

Dienstag, 12. September 2017

wrong permission on shm kills JAVA_JIT

We found a lot of trace files from several DBs on one of our DB Servers.
They look like:


*********_ora_26444.trc or *********_m000_5598.trc
*** 2017-09-08 15:11:29.181
*** SESSION ID:(632.5995) 2017-09-08 15:11:29.181
*** CLIENT ID:(SYSADMIN) 2017-09-08 15:11:29.181
*** SERVICE NAME:(****_****) 2017-09-08 15:11:29.181
*** MODULE NAME:(*::***:******.****.***.****.******) 2017-09-08 15:11:29.181
*** ACTION NAME:(/) 2017-09-08 15:11:29.181

peshmmap_Create_Memory_Map:
Map_Length = 4096
Map_Protection = 7
Flags = 1
File_Offset = 0
mmap failed with error 1
error message:Operation not permitted

*** 2017-09-08 15:11:29.181
Exception [type: SIGSEGV, Address not mapped to object] [ADDR:0x0] [PC:0x33BEF41, ioc_pin_shared_executable_object()+1509] [flags: 0x0, count: 1]
DDE: Problem Key 'ORA 7445 [ioc_pin_shared_executable_object()+1509]' was flood controlled (0x6) (incident: 61088)
ORA-07445: exception encountered: core dump [ioc_pin_shared_executable_object()+1509] [SIGSEGV] [ADDR:0x0] [PC:0x33BEF41] [Address not mapped to object] []
ssexhd: crashing the process...
Shadow_Core_Dump = PARTIAL
ksdbgcra: writing core file to directory '/***/diag/rdbms/***/***/cdump'

A quick search on MOS (and a opened SR) showedd as top result Ora‑7445 [Ioc_pin_shared_executable_object()] (Doc ID 1316906.1)

But the suggestions there did not solve the issue. (and we could not set java_jit_enabled = false due to application requirements).

But the Note was good enough to make me search more regarding /dev/shm, mmap and Operation not permitted.  This led to Shared executable memory on StackExchange. Again not a perfect fit, but it makes enough sense to guess:
with java_jit_enabled, the m000 process is doing the compilation (in time). To let the server process execute the compiled code, it's put into shared memory. This shared memory must be executable, otherwise the server process can not use it. So the memory is mapped with PROT_EXEC.
I checked on the affected host, if there is a reason against this:
> mount|grep shm    
tmpfs on /dev/shm type tmpfs (rw,nosuid,nodev,noexec,seclabel)

noexec prevents shared memory to be executed, so the memory mapping fails.

It's stated in Oracle Database Preinstallation Tasks
rw and execute permissions must be set, but noexec and nosuid must not be set.

this was changed after the DBs were installed. Probably for good intentions but with bad effects.

With the proper changes of the mount options, the test statement
SELECT dbms_java.longname('TEST') long_name FROM  dual;
completes without any error.



SecureFile LOB - managing free blocks

This blog post continues with all the objects and settings from SecureFile LOB - the empty tableSecureFile LOB - the 1st insert SecureFile LOB - the 1st update and SecureFile LOB - more inserts.

It starts with some inserts:
insert into berx.TEST_BLOBS
select 4, comments, file_content
from berx.source_blobs
where id=4;

commit;

insert into berx.TEST_BLOBS
select 5, comments, file_content
from berx.source_blobs
where id=1; 

insert into berx.TEST_BLOBS
select 6, comments, file_content
from berx.source_blobs
where id=4; 

insert into berx.TEST_BLOBS
select 7, comments, file_content
from berx.source_blobs
where id=1; 

insert into berx.TEST_BLOBS
select 8, comments, file_content
from berx.source_blobs
where id=4;

insert into berx.TEST_BLOBS
select 9, comments, file_content
from berx.source_blobs
where id=1; 

insert into berx.TEST_BLOBS
select 10, comments, file_content
from berx.source_blobs
where id=4; 

commit;

This leads to 10 lines with 10 LOBs. The LOBs are 1 or 2 blocks in size.

The LOBMAP summary of the rows and LOBs is this:

1 11.1 kB AABu7gAAEAAA+N7AAA

ROWID   = AABu7gAAEAAA+N7AAA
ROWNUM  = 1
LOBID   = 00000001000099BF531D
EXTENT# = 0
rdba   = 17032588 - 0x  103e58c
Block  = 255372
nblks  = 2
offset = 0
length = 11389

2 2-byte AABu7gAAEAAA+N/AAA

ROWID   = AABu7gAAEAAA+N/AAA
ROWNUM  = 2
LOBID   = 00000001000099BF67D1
EXTENT# = 0
rdba   = 17032590 - 0x  103e58e
Block  = 255374
nblks  = 1
offset = 0
length = 2

3 close to 4 kB AABu7gAAEAAA+N/AAB

ROWID   = AABu7gAAEAAA+N/AAB
ROWNUM  = 3
LOBID   = 00000001000099C090E3
EXTENT# = 0
rdba   = 17032587 - 0x  103e58b
Block  = 255371
nblks  = 1
offset = 0
length = 4038

4 11.1 kB AABu7gAAEAAA+N9AAA

ROWID   = AABu7gAAEAAA+N9AAA
ROWNUM  = 4
LOBID   = 00000001000099C56EFB
EXTENT# = 0
rdba   = 17032591 - 0x  103e58f
Block  = 255375
nblks  = 1
offset = 0
length = 8060
---
ROWID   = AABu7gAAEAAA+N9AAA
ROWNUM  = 5
LOBID   = 00000001000099C56EFB
EXTENT# = 1
rdba   = 17033787 - 0x  103ea3b
Block  = 256571
nblks  = 1
offset = 8060
length = 3329

This one is somehow special, as the LOB is 11kB in size, so it requires 2 blocks.
These 2 blocks are spread over 2 tablespace extents (and 2 LOB extents also).
 In this case space optimization won against avoiding fragmentation.

5 1-byte AABu7gAAEAAA+N/AAC

ROWID   = AABu7gAAEAAA+N/AAC
ROWNUM  = 6
LOBID   = 00000001000099C633A9
EXTENT# = 0
rdba   = 17033788 - 0x  103ea3c
Block  = 256572
nblks  = 1
offset = 0
length = 1

6 11.1 kB AABu7gAAEAAA+N/AAD

ROWID   = AABu7gAAEAAA+N/AAD
ROWNUM  = 7
LOBID   = 00000001000099C633AA
EXTENT# = 0
rdba   = 17033789 - 0x  103ea3d
Block  = 256573
nblks  = 2
offset = 0
length = 11389

7 1-byte AABu7gAAEAAA+N/AAE

ROWNUM  = 8
LOBID   = 00000001000099C633AB
EXTENT# = 0
rdba   = 17033791 - 0x  103ea3f
Block  = 256575
nblks  = 1
offset = 0
length = 1

8 11.1 kB AABu7gAAEAAA+N/AAF

ROWNUM  = 9
LOBID   = 00000001000099C633AC
EXTENT# = 0
rdba   = 17033792 - 0x  103ea40
Block  = 256576
nblks  = 2
offset = 0
length = 11389

9 1-byte AABu7gAAEAAA+N/AAG

ROWNUM  = 10
LOBID   = 00000001000099C633AD
EXTENT# = 0
rdba   = 17033794 - 0x  103ea42
Block  = 256578
nblks  = 1
offset = 0
length = 1

10 11.1 kB AABu7gAAEAAA+N/AAH

ROWID   = AABu7gAAEAAA+N/AAH
ROWNUM  = 11
LOBID   = 00000001000099C633AE
EXTENT# = 0
rdba   = 17033795 - 0x  103ea43
Block  = 256579
nblks  = 2
offset = 0
length = 11389

After row 4s commit, the NGLOB: Persistent Undo block changed:

Persistent Undo information

after row 4th commit
Block dump from disk:
buffer tsn: 4 rdba: 0x0103ea05 (4/256517)
scn: 0xa9d.9b8d2fe9 seq: 0x01 flg: 0x04 tail: 0x2fe94001
frmt: 0x02 chkval: 0x39b1 type: 0x40=NGLOB: Persistent Undo
Hex dump of block: st=0, typ_found=1
Dump of memory from 0x00007FDB0460C800 to 0x00007FDB0460E800
...
  Dump of Persistent Undo Block
  --------------------------------------------------------
 Inst: 1 Objd:454499 Inc:3472328295419215872 SyncTime:4126781815622353101 Flag:0x1
 Total: 2 LoadTime:1505116365 Opcode:1 Xid: 0x01b4.014.00002aca
  --------------------------------------------------------
Chunk: dba: 0x103ea3b: len: 1: Xid:  0x01b4.00d.00002abc: Scn: 2717.-1685245975: Flag: IN USE: FBR: False
Chunk: dba: 0x103ea3c: len: 68: Xid:  0x0000.000.00000000: Scn: 2708.1852084450: Flag: FREE: FBR: False

Block 0x103ea3b is marked as IN USE. This is the 2nd block from the LOB just inserted.
The remaining blocks in this LOB extent are marked as FREE.

After the other 6 inserts, some meta information changed again:

Persistent Undo information

after row 10th commit
Block dump from disk:
buffer tsn: 4 rdba: 0x0103ea05 (4/256517)
scn: 0xa9d.9d4b7340 seq: 0x01 flg: 0x04 tail: 0x73404001
frmt: 0x02 chkval: 0x5850 type: 0x40=NGLOB: Persistent Undo
Hex dump of block: st=0, typ_found=1
Dump of memory from 0x00007F880DC72800 to 0x00007F880DC74800
...
  Dump of Persistent Undo Block
  --------------------------------------------------------
 Inst: 1 Objd:454499 Inc:3472328295419215872 SyncTime:3473457525430831671 Flag:0x1
 Total: 5 LoadTime:1505118775 Opcode:1 Xid: 0x01af.000.00003334
  --------------------------------------------------------
Chunk: dba: 0x103ea3c: len: 1: Xid:  0x01af.021.00003338: Scn: 2717.-1655999709: Flag: IN USE: FBR: False
Chunk: dba: 0x103ea3d: len: 2: Xid:  0x01af.021.00003338: Scn: 2717.-1655999697: Flag: IN USE: FBR: False
Chunk: dba: 0x103ea3f: len: 4: Xid:  0x01af.021.00003338: Scn: 2717.-1655999697: Flag: IN USE: FBR: False
Chunk: dba: 0x103ea43: len: 8: Xid:  0x01af.021.00003338: Scn: 2717.-1655999680: Flag: IN USE: FBR: False
Chunk: dba: 0x103ea4b: len: 53: Xid:  0x0000.000.00000000: Scn: 2708.1852084450: Flag: FREE: FBR: False

There are several Persistent Undo Chunks now, with size of 1, 2, 4, 8 as IN USE and 53 FREE.
The LOBs from this insert are in the Chunks with len: 1, 2,4 and partially 8. To reflect the Chunk starting at 0x103ea43 with len: 8 is only partially filled (2 blocks for LOBID: 00000001000099C633AE) another structure is changed:

Hash Bucket - Range: 32k to 64k

Block dump from disk:
buffer tsn: 4 rdba: 0x0103e585 (4/255365)
scn: 0xa9d.9d4b7347 seq: 0x02 flg: 0x04 tail: 0x73473d02
frmt: 0x02 chkval: 0xdefc type: 0x3d=NGLOB: Hash Bucket
Hex dump of block: st=0, typ_found=1
Dump of memory from 0x00007F880DC72800 to 0x00007F880DC74800
...
  Dump of Hash Bucket Block
  --------------------------------------------------------
Hash Bucket Header Dump
Range: 32k to 64k
Inst:1 Flag:5 Total:0 FSG_COUNT:0 OBJD:454499 Inc:0
Self Descriptive
 fsg_count:0
Head:0x 0x00000000  Tail:0x 0x00000000
 Opcdode:0 Locker Xid: 0x0000.000.00000000
Fsbdba: 0x0    Fbrdba: 0x0
Head Cache Entries
-------------------
-------------------
Tail Cache Entries
-------------------
-------------------
Free Space Chunk Summary
Inst:1 Minc:0 Maxc:0 Count:1 Tot:6 MAXC:1
CFS Chunk List
--------------
Chunk:0 DBA: 0x0103ea45 Len:6 Xid: 0x01af.021.00003338 Ctime:0
Scn: 0x0000.00000000

This CFS Chunk list points to a chunk of 6 blocks (Len: 6) (size: 48k) starting with DBA: 0x103ea45 as free.

Here some meta information about used and unused blocks is stored in NGLOB: Persistent Undo and NGLOB: Hash Bucket blocks. It's also shown LOBs can be split up to fit into the first space available (against filling continuous blocks / least count of extents to avoid fragmentation).

Montag, 4. September 2017

SecureFile LOB - more inserts

This blog post continues with all the objects and settings from SecureFile LOB - the empty tableSecureFile LOB - the 1st insert and SecureFile LOB - the 1st update

The next insert is a small LOB with 2 bytes again:
insert into berx.TEST_BLOBS
select 2, comments, file_content
from berx.source_blobs
where id=2; 
--2 byte 
The table row points to a new block in the LOB segment:
ROWID   = AABu7gAAEAAA+N/AAA
ROWNUM  = 1
LOBID   = 00000001000099BF67D1
EXTENT# = 0
HOLE?   = n
Superchunk cont? = n
Overallocation  = n
rdba   = 17032590 - 0x  103E58E
File   = 4
Block  = 255374
nblks  = 1
offset = 0
length = 2
---

It's the 4th trans data block:

Block dump from disk:
buffer tsn: 4 rdba: 0x0103e58e (4/255374)
scn: 0xa9c.b1d49a00 seq: 0x02 flg: 0x04 tail: 0x9a000602
frmt: 0x02 chkval: 0x4617 type: 0x06=trans data
Hex dump of block: st=0, typ_found=1
Dump of memory from 0x00007FDC9B903800 to 0x00007FDC9B905800
7FDC9B903800 0000A206 0103E58E B1D49A00 04020A9C  [................]
...
Block header dump:  0x0103e58e
 Object id on Block? Y
 seg/obj: 0x6ef63  csc: 0xa9c.b1d49a00  itc: 1  flg: E  typ: 5 - LOCAL LOBS
     fsl: 0  fnx: 0xffffffff ver: 0x01

 Itl           Xid                  Uba         Flag  Lck        Scn/Fsc
0x01   0x01b0.011.000210a9  0x00000000.0000.00  -B--    0  fsc 0x0000.00000000
========
bdba    [0x0103e58e]
kdlich  [0x7fdc9b90384c 56]
  flg0  0x20 [ver=0 typ=data lock=n]
  flg1  0x00
  scn   0x0a9c.b1d49a00
  lid   00000001000099bf67d1
  rid   0x00000000.0000
kdlidh  [0x7fdc9b903864 24]
  flg2  0x00 [ver=0 lid=short-rowid hash=n cmap=n pfill=n]
  flg3  0x00
  pskip 0
  sskip 0
  hash  0000000000000000000000000000000000000000
  hwm   2
  spr   0
  data  [0x7fdc9b903880 52 8060]
41 42 00 6f 00 74 00 68 00 65 00 72 00 5f 00 78 00 6d 00 6c 00 3e 00 3c 00 69

The structure is well known already, lid is equal to LOBID, hwm is 2 bytes and the content is 0x41 0x42 which is A B.

There is no change in any of the Hash Bucket blocks (neither UFS nor CFS).



the 2nd insert is
insert into berx.TEST_BLOBS
select 3, comments, file_content
from berx.source_blobs
where id=3; 
--4 kbyte 

Again only 1 block.

ROWID   = AABu7gAAEAAA+N/AAB
ROWNUM  = 1
LOBID   = 00000001000099C090E3
EXTENT# = 0
HOLE?   = n
Superchunk cont? = n
Overallocation  = n
rdba   = 17032587 - 0x  103E58B
File   = 4
Block  = 255371
nblks  = 1
offset = 0
length = 4038
---

the LOB is now stored in 0x0103e58b - the 1st trans data block. It was used at the 1st insert, but not in use anymore since the 1st update - since then it was on the UFS list.

buffer tsn: 4 rdba: 0x0103e58b (4/255371)
scn: 0xa9c.b1d52068 seq: 0x02 flg: 0x04 tail: 0x20680602
frmt: 0x02 chkval: 0x7711 type: 0x06=trans data
Hex dump of block: st=0, typ_found=1
Dump of memory from 0x00007FF37EF64800 to 0x00007FF37EF66800
7FF37EF64800 0000A206 0103E58B B1D52068 04020A9C  [........h ......]
7FF37EF64810 00007711 00000005 0006EF63 B1D52068  [.w......c...h ..]
7FF37EF64820 00000A9C 00220001 FFFFFFFF 001D01A9  [......".........]
7FF37EF64830 00001782 00000000 00000000 00004000  [.............@..]
7FF37EF64840 00000000 00000000 00000000 B1D52068  [............h ..]
7FF37EF64850 00200A9C 01000000 C0990000 0000E390  [.. .............]
7FF37EF64860 00000000 00000000 00000000 00000000  [................]
7FF37EF64870 00000000 00000000 00000000 00000FC6  [................]
7FF37EF64880 6C636564 0D657261 2020200A 20202020  [declare..       ]
7FF37EF64890 44495220 20202020 574F5220 0D3B4449  [ RID     ROWID;.]
...
Block header dump:  0x0103e58b
 Object id on Block? Y
 seg/obj: 0x6ef63  csc: 0xa9c.b1d52068  itc: 1  flg: E  typ: 5 - LOCAL LOBS
     fsl: 0  fnx: 0xffffffff ver: 0x01

 Itl           Xid                  Uba         Flag  Lck        Scn/Fsc
0x01   0x01a9.01d.00001782  0x00000000.0000.00  -B--    0  fsc 0x0000.00000000
========
bdba    [0x0103e58b]
kdlich  [0x7ff37ef6484c 56]
  flg0  0x20 [ver=0 typ=data lock=n]
  flg1  0x00
  scn   0x0a9c.b1d52068
  lid   00000001000099c090e3
  rid   0x00000000.0000
kdlidh  [0x7ff37ef64864 24]
  flg2  0x00 [ver=0 lid=short-rowid hash=n cmap=n pfill=n]
  flg3  0x00
  pskip 0
  sskip 0
  hash  0000000000000000000000000000000000000000
  hwm   4038
  spr   0
  data  [0x7ff37ef64880 52 8060]

Also, nothing fancy here. Everything as expected.

There is another block of interest, the UFS Hash Bucket which UFS List points to this block. It did NOT change and still contains block 0x0103e58b:

Block dump from disk:
buffer tsn: 4 rdba: 0x0103e583 (4/255363)
scn: 0xa9c.916207e5 seq: 0x01 flg: 0x04 tail: 0x07e53d01
frmt: 0x02 chkval: 0xa4e3 type: 0x3d=NGLOB: Hash Bucket
Hex dump of block: st=0, typ_found=1
Dump of memory from 0x00007FF37EF64800 to 0x00007FF37EF66800
...
  Dump of Hash Bucket Block
  --------------------------------------------------------
Hash Bucket Header Dump
Inst:1 Flag:6 Total:0 FSG_COUNT:0 OBJD:454499 Inc:0
Self Descriptive
 fsg_count:0
Head:0x 0x00000000  Tail:0x 0x00000000
 Opcdode:3 Locker Xid: 0x01b0.019.00020f35
Fsbdba: 0x0    Fbrdba: 0x0
Head Cache Entries
-------------------
-------------------
Tail Cache Entries
-------------------
-------------------
Free Space Chunk Summary
Inst:0 Minc:0 Maxc:0 Count:0 Tot:0 MAXC:1
UFS List
--------------
Deleted - Chunk:0 DBA: 0x0103e58b Len:140681653780481 Xid: 0x01b0.019.00020f35 Ctime:1504343585
Scn: 0x0a9c.9062fe3c
  --------------------------------------------------------


this looks confusing: How can a block which is in use be present in a Free Space list?
My assumption here: as the blocks SCN (0x0a9c.b1d52068) is higher than the UFS entry SCN (0x0a9c.9062fe3c), I'd claim the UFS entry outdated and a cleanup will happen when there is a need to write this Hash Bucket block.