Tales From A Lazy Fat DBA

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Archive for June, 2022

Exceptionally high stats collection time on FIXED OBJECTS during an upgrade …

Posted by FatDBA on June 26, 2022

Someone recently asked about a situation where they were trying to upgrade their database to 19c and as a part of their upgrade plan, they were trying to run fixed object statistics but it was going on forever, and they were totally clueless why and where its taking time. This being a mandatory step, they tried several times, but same result.

About fixed object stats, It is recommended that you re-gather them if you do a major database or application upgrade, implement a new module, or make changes to the database configuration. For example if you increase the SGA size then all of the X$ tables that contain information about the buffer cache and shared pool may change significantly, such as X$ tables used in v$buffer_pool or v$shared_pool_advice.

About fixed objects stats collection idle time, I mean anything between 1-10 minutes is I will say normal and average, but anything that goes beyond 20 minutes or even more or even in hours is abnormally high and points to a situation.

So, I was asked to take a look on ad-hoc basis and during the analysis I found a SQL trying to do a count all on unified_audit_trail, and was running from the same time since they called the DBMS_STATS for FIXED OBJECTS on the database. When asked, they told me that they’d enabled auditing on the database some 6 months back and haven’t purged anything since then, the audit trail had grown behemoth and has ~ 880 Million records. I immediately offered them two approaches to handle the situation – Either lock your unified table statistics (using dbms_stats.lock_table_stats) or else take backup of the table and purge audit records before calling the stats gathering job again. They agreed with the second approach, they took backup of audit table and purged audit trail. As soon as they purged audit table, the stats collection on fixed objects got finished in ~ 3 minutes.

This was the situation and what we did …

SQL> select * from dba_audit_mgmt_last_arch_ts;

AUDIT_TRAIL RAC_INSTANCE LAST_ARCHIVE_TS
-------------------- ------------ ------------------------------
STANDARD AUDIT TRAIL 0 22-MAY-22 06.00.00.000000 AM +00:00


SQL> select count(*) from aud$;

COUNT(*)
----------
885632817

BEGIN
DBMS_AUDIT_MGMT.clean_audit_trail(
audit_trail_type => DBMS_AUDIT_MGMT.AUDIT_TRAIL_AUD_STD,
use_last_arch_timestamp => FALSE);
END;
/

SQL> select count(*) from aud$;

COUNT(*)
----------
0


SQL> SET TIMING ON
SQL> BEGIN
DBMS_STATS.GATHER_FIXED_OBJECTS_STATS;
END;
/

Elapsed: 00:03:10.81

Hope It Helped!
Prashant Dixit

Posted in Advanced, troubleshooting | Tagged: , , , , | 2 Comments »

What is that strange looking wait event ‘TCP Socket (KGAS)’ in AWR report ?

Posted by FatDBA on June 13, 2022

Hi Guys,

Recently someone shared me an AWR report from a production 19c system, and he was very tensed about one of the strange looking wait event called ‘TCP Socket (KGAS)’. He was strained because the event was coming with a very high average wait time of 7863.68ms (7.86 seconds), and was consuming around 98.0% of the total DB Time.

Luckily I’d encountered something similar in the past for one of the customer, where the application team was unable to send the mail as DBMS scheduler, and it was stuck for a long time with wait event “TCP Socket(KGAS)” where problem was not with the scheduler, but was an underlying network or third-party application problem.

So, today’s post is all about the wait event, what it is, how to resolve it etc.

KGAS is a element in the server which handles TCP/IP sockets which is typically used in dedicated connections i.e. by some PLSQL built in packages such as UTL_HTTP and UTL_TCP.
A session is waiting for an external host to provide requested data over a network socket. The time that this wait event tracks does not indicate a problem, and even a long wait time is not a reason to contact Oracle Support. It naturally takes time for data to flow between hosts over a network, and for the remote aspect of an application to process any request made to it. An application that communicates with a remote host must wait until the data it will read has arrived.

From an application/network point of view, delays in establishing a network connection may produce unwanted delays for users. We should make sure that the application makes network calls efficiently and that the network is working well such that these delays are minimized.

From the database point of view, these waits can safely be ignored; the wait event does not represent a database issue. It merely reports the total elapsed time for a network connection to be established or for data to arrive from over the network. The database waits for the connection to be established and reports the time taken. Its always good to check with the network or the third-party application vendors to investigate the underlying socket.

But in case of systemwide waits – If the TIME spent waiting for this event is significant then it is best to determine which sessions are showing the wait and drill into what those sessions are doing as the wait is usually related to whatever application code is executing eg: What part of the application may be using UTL_HTTP or similar and is experiencing waits. This statement can be used to see which sessions may be worth tracing

SELECT sid, total_waits, time_waited
FROM v$session_event WHERE event='TCP Socket (KGAS)' and total_waits>0 ORDER BY 3,2;

In order to reduce these waits or to help find the origin of the socket operations try:

  • Check the current SQL/module/action of V$SESSION for sessions that are waiting on the event at the time that they are waiting to try and identify any common area of application code waiting on the event.
  • Get an ERRORSTACK level 3 dump of some sessions waiting on the event. This should help show the exact PLSQL and C call stacks invoking the socket operation if the dump is taken when the session is waiting. Customers may need assistance from Oracle Support in order to get and interpret such a dump but it can help pinpoint the relevant application code.
  • Trace sessions incurring the waits including wait tracing to try and place the waits in the context of the code executing around the waits. eg: Use event 10046 level 8 or DBMS_MONITOR.SESSION_TRACE_ENABLE.
  • Use DBA_DEPENDENCIES to find any application packages which may ultimately be using UTL_HTTP or UTL_TCP underneath for some operation.

Example:
Execute the following SQL from a session on a dedicated connection and then check the resulting trace file to see “TCP Socket (KGAS)” waits:

alter session set events '10046 trace name context forever, level 8';

Hope It Helped!
Prashant Dixit

Posted in Advanced, troubleshooting | Tagged: , , | Leave a Comment »

FatDBA ranked 27th among top 100 Oracle database blogs on the planet … :)

Posted by FatDBA on June 4, 2022

Hello All, my blog FatDBA have been awarded with the ‘Top 100 Oracle Blogs on the planet‘ (Rank 27) by feedspot. The best Oracle blog list curated from thousands of blogs on the web and ranked by traffic, social media followers, domain authority & freshness.

Thank you so much guys for your support \,,/

https://blog.feedspot.com/oracle_blogs/

Posted in Uncategorized | Tagged: | Leave a Comment »

Oracle 21c welcomes the ‘Attention Log’ …

Posted by FatDBA on June 1, 2022

Hi Guys,

Alert log is always been a very important logfile which contain important information about error messages and exceptions that occur during database operations. Its very crucial for any analysis or for troubleshooting any critical event that has happened. Specially over the period of last few years, with all those new database releases, its slowly becoming very messy, loud and has got whole lot of new content added to it that it has to record for all those regular and critical database events, and finally with the inception of Oracle 21c we have the ‘Attention Log‘ that helps to segregate all those critical and vital events which otherwise gets mixed up with other regular incidents of alertlog file.

Each of the database has its own Attention log and is a regular JSON format file which is very easy to translate. Few of the important dimensions or its properties are
URGENCY: Class with possible values INFO, IMMEDIATE etc.
CAUSE : A quick detail about the possible cause or reason.
NOTIFICATION : A regular message in case of any event i.e. “PMON (ospid: 1901): terminating the instance due to ORA error 12752” etc.
ACTION : What possibly you can do
TIME : A timestamp of the event

Let’s see how it looks like!

[oracle@witnessalberta ~]$ !sql
sqlplus / as sysdba

SQL*Plus: Release 21.0.0.0.0 - Production on Fri Apr 8 22:38:25 2022
Version 21.3.0.0.0

Copyright (c) 1982, 2021, Oracle.  All rights reserved.


Connected to:
Oracle Database 21c Enterprise Edition Release 21.0.0.0.0 - Production
Version 21.3.0.0.0

SQL> set linesize 400 pagesize 400


SQL> col NAME for a30
SQL> col value for a70
SQL>
SQL> select name, value from v$diag_info where value like '%attention%';

NAME                           VALUE
------------------------------ ----------------------------------------------------------------------
Attention Log                  /opt/oracle/diag/rdbms/orclcdb/ORCLCDB/trace/attention_ORCLCDB.log




[oracle@witnessalberta trace]$ pwd
/opt/oracle/diag/rdbms/orclcdb/ORCLCDB/trace
[oracle@witnessalberta trace]$

[oracle@witnessalberta trace]$
[oracle@witnessalberta trace]$ ls -ltrh *.log*
-rw-r-----. 1 oracle oinstall 6.0K Apr  8 22:32 attention_ORCLCDB.log
-rw-r-----. 1 oracle oinstall 244K Apr  8 22:34 alert_ORCLCDB.log
[oracle@witnessalberta trace]$




{
  "NOTIFICATION" : "Starting ORACLE instance (normal) (OS id: 3309)",
  "URGENCY"      : "INFO",
  "INFO"         : "Additional Information Not Available",
  "CAUSE"        : "A command to startup the instance was executed",
  "ACTION"       : "Check alert log for progress and completion of command",
  "CLASS"        : "CDB Instance / CDB ADMINISTRATOR / AL-1000",
  "TIME"         : "2022-04-08T22:32:47.914-04:00"
}

....
.....
.........
{
  "NOTIFICATION" : "Shutting down ORACLE instance (immediate) (OS id: 9724)",
  "URGENCY"      : "INFO",
  "INFO"         : "Shutdown is initiated by sqlplus@localhost.ontadomain (TNS V1-V3). ",
  "CAUSE"        : "A command to shutdown the instance was executed",
  "ACTION"       : "Check alert log for progress and completion of command",
  "CLASS"        : "CDB Instance / CDB ADMINISTRATOR / AL-1001",
  "TIME"         : "2021-09-16T23:11:56.812-04:00"
}

.....
......
........

{
  "ERROR"        : "PMON (ospid: 1901): terminating the instance due to ORA error 12752",
  "URGENCY"      : "IMMEDIATE",
  "INFO"         : "Additional Information Not Available",
  "CAUSE"        : "The instance termination routine was called",
  "ACTION"       : "Check alert log for more information relating to instance termination rectify the error and restart the instance",
  "CLASS"        : "CDB Instance / CDB ADMINISTRATOR / AL-1003",
  "TIME"         : "2021-09-16T23:34:26.117-02:00"
}
...
.....
......
{
  "ERROR"        : "PMON (ospid: 3408): terminating the instance due to ORA error 474",
  "URGENCY"      : "IMMEDIATE",
  "INFO"         : "Additional Information Not Available",
  "CAUSE"        : "The instance termination routine was called",
  "ACTION"       : "Check alert log for more information relating to instance termination rectify the error and restart the instance",
  "CLASS"        : "CDB Instance / CDB ADMINISTRATOR / AL-1003",
  "TIME"         : "2022-04-08T23:38:11.258-04:00"
}


Hope It Helped!
Prashant Dixit

Posted in Basics, troubleshooting | Tagged: , | Leave a Comment »

 
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