DB locking issue
Oracle database - analyzing a deadlock [ORA-00060]
As a weblogic administrator the interaction among the application server and the database is often strong. In fact, according to Confio Software (2013) approximately 70% of applications’ performance problems are caused by the database. Whit this in mind, knowing some methods or common cases about the database performance is a relevant skill for application server administrators. The aim of this post is to describe how a performance problem that caused the crash of the database and the application server was solved through the analysis of the TRC file generated by the Oracle database.
The system affected
The system who suffered that problem was used by an important company.
- At peak hours the credit evaluation module was slower.
- During the financial close periods the database had to be restarted at least three times.
- The application server was affected by the database contention and it had to be restarted.
- Hundreds of locks were identified on the database.
- Some deadlocks were detected on the database.
- Most locks were generated by delete sentences like this:
DELETE FROM Table_A WHERE CREDITEVALUATIONID = :B DELETE FROM Table_A WHERE CREDITEVALUATIONID = :B DELETE FROM Table_A WHERE CREDITEVALUATIONID = :B DELETE FROM Table_A WHERE CREDITEVALUATIONID = :B
It was clear we had a deadlock problem, but we needed the root cause. It was found using the TRC file generated by the Oracle database and the sources of information that can be found in the references section within this document.
This is the TRC generated at that time:
/ora_control/admin/xxxxx/udump/ora_24473.trc Oracle Database 10g Enterprise Edition Release 10.2.0.4.0 - 64bit Production With the Partitioning, Data Mining and Real Application Testing options ORACLE_HOME = /oracle10/product/db/10.2.0 System name: test Node name: test Release: B.11.11 Version: U Machine: test Instance name: test Redo thread mounted by this instance: 1 Oracle process number: 1087 Unix process pid: 24473, image: oracle@****** *** 2012-01-31 19:26:46.853 *** ACTION NAME:() 2012-01-31 19:26:46.845 *** MODULE NAME:(JDBC Thin Client) 2012-01-31 19:26:46.845 *** SERVICE NAME:(SYS$USERS) 2012-01-31 19:26:46.845 *** SESSION ID:(3988.49756) 2012-01-31 19:26:46.845 DEADLOCK DETECTED ( ORA-00060 ) [Transaction Deadlock] The following deadlock is not an ORACLE error. It is a deadlock due to user error in the design of an application or from issuing incorrect ad-hoc SQL. The following information may aid in determining the deadlock: Deadlock graph: ---------Blocker(s)-------- ---------Waiter(s)--------- Resource Name process session holds waits process session holds waits TM-0004a1a4-00000000 1087 3988 SX SSX 733 3151 SX SSX TM-0004a1a4-00000000 733 3151 SX SSX 1087 3988 SX SSX session 3988: DID 0001-043F-0003D9CF session 3151: DID 0001-02DD-000FE20F session 3151: DID 0001-02DD-000FE20F session 3988: DID 0001-043F-0003D9CF Rows waited on: Session 3151: no row Session 3988: no row Information on the OTHER waiting sessions: Session 3151: pid=733 serial=40226 audsid=292398699 user: 1633/TEST O/S info: user: SYSTEM, term: unknown, ospid: 1234, machine: xxxxxxxxxx program: JDBC Thin Client application name: JDBC Thin Client, hash value=2546894660 Current SQL Statement: DELETE FROM Table_A WHERE CREDITEVALUATIONID = :B End of information on OTHER waiting sessions. Current SQL statement for this session: DELETE FROM Table_A WHERE CREDITEVALUATIONID = :B ----- PL/SQL Call Stack ----- object line object handle number name c0000003bbe25980 1941 package body ************************* c0000003bbe25980 2470 package body ************************* c00000035ce033a0 12 procedure ****************************** c00000035ae75f88 1 anonymous block
As can be seen in the previous trace it is evident than some delete sentences are related to the problem, it makes sense with the sentences shown in the symptoms section.
The most important piece of information given by the previous trace is the following
---------Blocker(s)-------- ---------Waiter(s)--------- Resource Name process session holds waits process session holds waits TM-0004a1a4-00000000 1087 3988 SX SSX 733 3151 SX SSX TM-0004a1a4-00000000 733 3151 SX SSX 1087 3988 SX SSX
The TM (at the beginning of each line) means that the lock found in the trace is table lock caused by the application and often generated by relationships between parent and child tables without indexing the foreign key (Burleson D., n.d).
This problem is also described by [Oracle] (https://asktom.oracle.com/pls/asktom/f?p=100:11:0::::P11_QUESTION_ID:1528515465282).
How can I identify the tables involved in this deadlock? I have to use this data: TM-0004a1a4-00000000 , the number remarked has to be converted from hexadecimal to decimal. In that case I got 303524, whit this data you have to execute this query:
SELECT * FROM dba_objects WHERE object_id= 303524;
The previous query returns the locked object that in my case was: Table_C
Now we had to execute this query to get the relationships between this table and others:
SELECT c.TABLE_NAME,c.* FROM ALL_CONSTRAINTS c WHERE CONSTRAINT_TYPE='R' AND R_CONSTRAINT_NAME IN (SELECT CONSTRAINT_NAME FROM ALL_CONSTRAINTS WHERE CONSTRAINT_TYPE IN ('P','U') AND TABLE_NAME='Table_C');
Or you can use a tool to get the relationships visually. In that case, I got this
The previous image shows that Table_C has a relationship by FK (column CREDITEVALUATIONID) with the table Table_A. However, this FK is not indexed and this was the root cause of that problem.
After that a query was executed to detect other cases like this and after fixing them, the performance of that module was improved.
This is an example of reactive support. However, we can use health checks to discover these kinds of problems in advance (proactive support). In fact, [SYSCO AS] (http://www.sysco.no) is investing a lot of time on providing health checks to identify database problems before they happen.
Confio Software (2013) The Missed Opportunity for Improved Application Performance [Online document] Available from: http://cdn.swcdn.net/creative/v13.2/pdf/Whitepapers/DevOps_Essentials_DBAs_%20Developers_WP_Confio_May2014.pdf (Accessed: 30 June, 2015)
Houri Mohamed (2012) Mohamed Houri’s Oracle Notes Performance [Online document] Available from: http://hourim.wordpress.com/category/deadlock/ (Accessed: 30 June, 2015)
Burleson Donald (n.d.) Oracle Metric TM http://www.dba-oracle.com/m_tm.htm [Online document] Available from: http://hourim.wordpress.com/category/deadlock/ (Accessed: 30 June, 2015)
Oracle (2015)Troubleshooting “ORA-00060 Deadlock Detected” Errors [ID 62365.1] [Online document] Available from: support.oracle.com (Accessed: 30 June, 2015)
Oracle (n.d) Andre – Thanks for the question regarding “Reading deadlock trace files”, version 8.1.5 [Online document] Available from: https://asktom.oracle.com/pls/asktom/f?p=100:11:0::::P11_QUESTION_ID:1528515465282 (Accessed: 30 June, 2015)