During a 11gR1 Clusterware installation for a Single Instance Failover Cluster at a customer site, I have experienced an interesting behaviour, which was caused by an Oracle Bug.

The environment was:

• 2 Node Oracle Clusterware 11.1.0.7 Cluster on Linux x86_64 using latest Recommended Patches as of October 19th. (pre PSU 11.1.0.7.1)
• Clusterware installed as unix user crs
• ASM installed as unix user oracle

The ASM instances could be started with SQL*Plus without any problems, but if the ASM instances were started by means of clusterware using srvctl (either from root, crs or oracle) the  ASM instances would crash at diskgroup mount with:

ORA-07445: exception encountered: core dump  [sskgds_find_rtn_hdr()+1171]
[SIGBUS] [ADDR:0x2AACD701342C] [PC:0x25799DF]
[Non-existent physical address] []

Oracle Support identified this behaviour as Bug 6952915, for which there are patches for Linux x86, x86_64 and Solaris Sparc64.

I have encountered the following problem on a 10.2.0.4 database on Linux x86_64 today:
A user session has been waiting for “enq: RO – fast object reuse” for almost 60 minutes while executing a “truncate table” SQL statement.

SQL> select username, event, sql_id, taddr, last_call_et from v$session where sid = 234;

USERNAME EVENT SQL_ID TADDR LAST_CALL_ET
———- —————————– ————- —————- ————
MD enq: RO – fast object reuse ljk299jlkj003 0000000153264570 3542

SQL> select sql_text from v$sqlstats where sql_id = ‘ljk299jlkj003’;

SQL_TEXT
————————————-
truncate table tab1

The Session was blocked by the CKPT process:

SQL> select * from dba_waiters;

WAITING_SESSION HOLDING_SESSION LOCK_TYPE MODE_HELD MODE_REQUESTED LOCK_ID1 LOCK_ID2
————— ————— ————————– —————————————- —————————————- ———- ———-
234 423 RO Row-S (SS) Exclusive 65573 1

SQL> select sid, serial#, sql_id, last_call_et, machine, program, username from v$session where sid = 423;

SID SERIAL# SQL_ID LAST_CALL_ET MACHINE PROGRAM
———- ———- ————- ———— —————- ——————————–
423 1 4133636 ora-vm1.intra oracle@ora-vm1.intra (CKPT)

The checkpoint process was waiting for database writer DBWR process, which was spinning on one cpu:

top

PID USER PR NI VIRT RES SHR S %CPU %MEM TIME+ COMMAND
10712 oracle 25 0 2201m 1.7g 1.7g R 99.5 21.7 108:18.03 oracle

PID 10712 maps to DBW0:

[oracle@ora-vm1 ]$ ps -ef|grep 10712
oracle 10712 1 0 2008 ? 03:23:05 ora_dbw0_MDDB01

mpstat

Linux 2.6.9-78.ELsmp (ora-vm1.intra) 01/20/2009

02:21:56 PM CPU %user %nice %system %iowait %irq %soft %idle intr/s
02:21:57 PM all 49.75 0.00 0.00 0.00 0.00 0.00 50.25 1055.00
02:21:57 PM 0 0.00 0.00 0.00 0.00 0.00 0.00 100.00 1006.00
02:21:57 PM 1 100.00 0.00 0.00 0.00 0.00 0.00 0.00 49.00

02:21:57 PM CPU %user %nice %system %iowait %irq %soft %idle intr/s
02:21:58 PM all 50.75 0.00 0.00 0.50 0.00 0.00 48.76 1161.00
02:21:58 PM 0 1.00 0.00 0.00 1.00 0.00 0.00 98.00 1087.00
02:21:58 PM 1 100.00 0.00 0.00 0.00 0.00 0.00 0.00 74.00

The stack of dbw0 during the time showed these signatures:

[oracle@ora-vm1 oracle]$ pstack 10712
#0 0x000000000074b7fb in kslfre ()
#1 0x00000000010ccc3b in kcbo_exam_buf ()
#2 0x00000000010d0d62 in kcbo_service_ockpt ()
#3 0x0000000001080cd7 in kcbbdrv ()
#4 0x00000000007ddcc2 in ksbabs ()
#5 0x00000000007e4b32 in ksbrdp ()
#6 0x0000000002efcb50 in opirip ()
#7 0x00000000012da326 in opidrv ()
#8 0x0000000001e62456 in sou2o ()
#9 0x00000000006d2555 in opimai_real ()
#10 0x00000000006d240c in main ()
[oracle@ora-vm1 oracle]$ pstack 10712
#0 0x000000000074b36d in kslfre ()
#1 0x00000000010cc203 in kcbo_write_process ()
#2 0x00000000010ce608 in kcbo_write_q ()
#3 0x0000000001080a6d in kcbbdrv ()
#4 0x00000000007ddcc2 in ksbabs ()
#5 0x00000000007e4b32 in ksbrdp ()
#6 0x0000000002efcb50 in opirip ()
#7 0x00000000012da326 in opidrv ()
#8 0x0000000001e62456 in sou2o ()
#9 0x00000000006d2555 in opimai_real ()
#10 0x00000000006d240c in main ()
[oracle@ora-vm1 oracle]$ pstack 10712
#0 0x00000000010ccb60 in kcbo_exam_buf ()
#1 0x00000000010d0d62 in kcbo_service_ockpt ()
#2 0x0000000001080cd7 in kcbbdrv ()
#3 0x00000000007ddcc2 in ksbabs ()
#4 0x00000000007e4b32 in ksbrdp ()
#5 0x0000000002efcb50 in opirip ()
#6 0x00000000012da326 in opidrv ()
#7 0x0000000001e62456 in sou2o ()
#8 0x00000000006d2555 in opimai_real ()
#9 0x00000000006d240c in main ()
[oracle@ora-vm1 oracle]$ pstack 10712
#0 0x00000000010d0da5 in kcbo_service_ockpt ()
#1 0x0000000001080cd7 in kcbbdrv ()
#2 0x00000000007ddcc2 in ksbabs ()
#3 0x00000000007e4b32 in ksbrdp ()
#4 0x0000000002efcb50 in opirip ()
#5 0x00000000012da326 in opidrv ()
#6 0x0000000001e62456 in sou2o ()
#7 0x00000000006d2555 in opimai_real ()
#8 0x00000000006d240c in main ()

A MetaLink Research for the term “kcbo_service_ockpt” leads to Bug 7376934, which is a duplicate of Bug 7385253 – DBWR IS CONSUMING HIGH CPU.

Patch 7385253 is available for Linux x86_64, HP-UX, Solaris, AIX.
Reference:
MetaLink Note 762085.1 – Subject: ‘enq: RO – fast object reuse’ contention when gathering schema/table statistics in parallel

When upgrading from pre 10.2.0.4 to 10.2.0.4, Oracle enables NUMA support. This has the effect that there can be multiple shared memory segments (MetaLink Note: 429872.1) although shmmax/shmall are set to high values.

I have read MetaLink Notes (7171446.8, 6730567.8, 6689903.8) and this blog entry, where a customer had problems on HP-UX with the default NUMA settings.

Better than that, it can also lead to instance crashes in 10.2.0.4 as reported in MetaLink Note 743191.1. Good news is that there is a patch available for Linux x86_64/10.2.0.4.

I have asked Oracle Support whether it is safe to leave NUMA enabled for Linux Itanium, but they would not comment on it. Instead they asked me to check with the OS vendor. Great. ;-(