ORA-00060

How to Identify ORA-00060 Deadlock Types Using Deadlock Graphs in Trace (Doc ID 1507093.1)

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Oracle Database - Enterprise Edition - Version 9.0.1.0 and later
Oracle Database Cloud Schema Service - Version N/A and later
Oracle Database Exadata Express Cloud Service - Version N/A and later
Gen 1 Exadata Cloud at Customer (Oracle Exadata Database Cloud Machine) - Version N/A and later
Oracle Cloud Infrastructure - Database Service - Version N/A and later
Information in this document applies to any platform.

Goal

When Oracle detects a deadlock, the current SQL in the session detecting the deadlock is cancelled and 'statement-level rollback' is performed so as to free up resources and not block all activity. The session that detected the deadlock is still 'alive' and the rest of the transaction is still active. If you repeat the last (cancelled) operation in the session, then you will get the deadlock again.

When such a deadlock is detected a trace file is produced containing a "Deadlock Graph" (along with other useful information). By examination of numerous Service Requests, we have seen that the most common types of deadlock can be identified by a "signature" deadlock graph that can be used to identify the "type" of deadlock being encountered. This article presents examples of each type so that investigation and resolution can continue along the right track.

The aim of this document is to show how to use a "Deadlock Graph" produced by and ORA-00060 error to identify the base problem.

NOTE: Some deadlock traces DO NOT contain a "Deadlock Graph"  section because the deadlock is such that it would be inappropriate or irrelevant. In these cases then the recommended action is to collect some extra diagnostic information and then create a Service Request with Support as outlined in the following document:

Document 1552194.1 ORA-00060 Deadlock Graph Not Matching any Examples: Suggested Next Steps

If you are not already using it, you can use the Troubleshooting Assistant to help you diagnose common ORA-00060 Deadlock issues:

Document 60.1 Troubleshooting Assistant: Oracle Database ORA-00060 Errors on Single Instance (Non-RAC) Diagnosing Using Deadlock Graphs in ORA-00060 Trace Files

Deadlock Graph Interpretation

A typical deadlock graph might look like this:

 

In order to differentiate different types, we have taken the Lock Type and the mode held/waited for by the holder and waiter and used this to create a signature for each type. For example, the previous graph shows the following characteristics:

• >1 row in the Deadlock Graph
• All Lock Types are TX
• The lock modes for the Holders and the Waiters are all X (eXclusive, mode 6)

By focusing on these particular characteristics in the graph:

 

will give us the following type (which is typically an application deadlock):

TX X X
TX X X

Note that the most relevant parts of the "Key Signature" for deadlock type recognition are the lock Type and the Mode it is requesting. The main types are highlighted in the table below

The most common types are:

"Key Signature"	Lock Type	Requested Lock Mode	Deadlock Graph	Likely Deadlock Type	Comments
Type TX Lock Requesting Mode X (6)	TX	X(6)	TX X X TX X X	Application	TX Lock Held in Mode X (6) Requesting Mode X (6)
Type TM Lock Requesting Mode SSX (5)	TM	SSX (5)	TM SX SSX SX SSX TM SX SSX SX SSX	Missing Index on Foreign Key (FK) Constraint	TM  Lock Held in Mode SX (3) Held SSX (5) Requested
Type TX Lock Requesting Mode S(4)	TX	S(4)	TX X S TX X S	Insufficient Interested Transaction List (ITL) Provision OR Bitmap Index OR PK/UK Index	TX Lock Held in Mode X (6) Requesting Mode S (4) ITL, Bitmap Index and PK/UK Index Signatures are the Same. Further Investigation will be required to identify absolute cause
Type TX Lock Requesting Mode X (6) Single Row in Deadlock Graph	TX	X(6)	TX X X Single Row in Deadlock Graph	Self Deadlock OR Autonomous Transaction Self Deadlock	This looks the same as a standard application deadlock except that there is only a single row in the deadlock graph.
Type UL Lock in Deadlock Graph	UL	ANY	UL ? ? ?	Application Deadlock Featuring User Defined Locks	This is very similar to the standard application deadlock except that it features User Defined Locks

 

Note: this table is not exhaustive and outlines the most common issues. There are some rare conditions where deadlocks can be achieved that are not mentioned. For cases that do not match those above, the recommended action is to collect some extra diagnostic information and then create a Service Request with Support as outlined in the following document:

Document 1552194.1 ORA-00060 Deadlock Graph Not Matching any Examples: Suggested Next Steps

For information on how to identify and diagnose the various different types of ORA-00060 Deadlock Types that you may encounter, please refer to the following document:

Document 1559695.1 How to Diagnose Different ORA-00060 Deadlock Types Using Deadlock Graphs in Trace

Note: these are the most common types and causes. There are rare cases where similar symptoms can be found with different causes. If there is any doubt about the identification of a particular non-application deadlock type or if different graphs are seen, then file a Service Request with Oracle Support

For Reference, the Oracle lock modes are :

0 - none
1 - null (NULL)
2 - Row Share, also called a subshare table lock  (SS)
3 - Row eXclusive Table Lock, also called a subexclusive table lock (SX)
4 - Share Table Lock (S)
5 - Share Row-eXclusive, also called a share-subexclusive table lock (SSX)
6 - EXclusive (X)

Note: Often you will see a combination of an application deadlock "Signature" plus one of the others as opposed to a "classic" repeating signature. For example you may see something like:

Deadlock graph:
                     ---------Blocker(s)--------  ---------Waiter(s)---------
Resource Name          process session holds waits  process session holds waits
TM-XXXXXXXX-00000000　      11     333    SX             22      44    SX   SSX
TX-XXXXXXXX-XXXXXXXX　      22      44     X             11     333           X

 
Which is a combination of the "Application deadlock" and "Missing Index on Foreign Key (FK) Constraint" deadlock. In these cases, it is advisable to resolve the non-"TX X X" symptoms first since it is more likely that the less common FK/ITL/Bitmap signature is the base cause as opposed to an application deadlock.

 

Please Note that the trace contains various associated pieces of information that may or may not have any relevance to the issue dependent on the type of deadlock. For example, in the "Rows Waited on:" Section, the "dictionary objn" value can be used to identify related objects in certain cases, but in other cases may point at totally unrelated information. If the information is useable, it is noted in the relevant section, otherwise, do not rely upon it.

There is more about lock modes and locking in the following:

Oracle® Database Concepts
12c Release 1 (12.1)
E17633-20
Chapter 9 Data Concurrency and Consistency
Section: Lock Modes
https://docs.oracle.com/database/121/CNCPT/consist.htm#CNCPT020

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Solution

For information on how to identify and diagnose the various different types of ORA-00060 Deadlock Types that you may encounter, please refer to the following document:

Document 1559695.1 How to Diagnose Different ORA-00060 Deadlock Types Using Deadlock Graphs in Trace  

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