This about transaction deadlocks resulting from an index missing on foreign key colum(s). Actually, the post will not dive into the odds resulting from this failure but show how to detect this dedicated reason for an “ORA-00060: deadlock detected while waiting for resource” message. In particular, what to look out for in the trace file and how to find the table objects (instead of rows) being deadlocked against each other. The best resource on the web tackling this subject is of course (Reading deadlock trace files) from Tom Kyte, which also guided me along the way of a “no row deadlock”, see below.
Ok, on first place, some tool, Enterprise Manager for example, or whatever will notify you about entries in the
alert.log, reading roughly the like as “Sun May 29 02:51:07 2016 ORA-00060: Deadlock detected. More info in file H:\ORACLE\diag\rdbms\got\got\trace\got_ora_4536.trc“. Inspecting the trace file, you should focus your attention on the first 70 lines, in most cases neglegting the trailing process information dumps. I got this, anything noteworthy will be highlighted and discussed below:
Oracle Database 11g Enterprise Edition Release 188.8.131.52.0 - 64bit Production With the Partitioning, OLAP, Data Mining and Real Application Testing options Windows NT Version V6.1 Service Pack 1 CPU : 4 - type 8664, 4 Physical Cores Process Affinity : 0x0x0000000000000000 Memory (Avail/Total): Ph:3493M/16383M, Ph+PgF:19457M/32764M VM name : VMWare Version (6) Instance name: got Redo thread mounted by this instance: 1 Oracle process number: 167 Windows thread id: 6960, image: ORACLE.EXE (J001) *** 2016-12-09 12:16:58.820 *** SESSION ID:(447.46153) 2016-12-09 12:16:58.820 *** CLIENT ID:() 2016-12-09 12:16:58.820 *** SERVICE NAME:(SYS$USERS) 2016-12-09 12:16:58.820 *** MODULE NAME:(srch_queue_mgr.set_iu_event) 2016-12-09 12:16:58.820 *** ACTION NAME:(BLD) 2016-12-09 12:16:58.820 *** 2016-12-09 12:16:58.820 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-0001e2cf-00000000 167 447 SX SSX 172 38 SX SSX TM-0001e2cf-00000000 172 38 SX SSX 167 447 SX SSX session 447: DID 0001-00A7-004D3814 session 38: DID 0001-00AC-001DCB08 session 38: DID 0001-00AC-001DCB08 session 447: DID 0001-00A7-004D3814 Rows waited on: Session 447: no row Session 38: no row ----- Information for the OTHER waiting sessions ----- Session 38: sid: 38 ser: 53179 audsid: 319758247 user: 70/HUGO flags: (0x8010041) USR/- flags_idl: (0x1) BSY/-/-/-/-/- flags2: (0x40009) -/-/INC pid: 172 O/S info: user: svc_dbprd, term: DBPRD, ospid: 6104 image: ORACLE.EXE (J000) client details: O/S info: user: svc_dbprd, term: DBPRD, ospid: 6104 machine: DBPRD program: ORACLE.EXE (J000) application name: srch_queue_mgr.set_iu_event, hash value=2326741934 action name: BLD, hash value=1673980416 current SQL: DELETE FROM thattable WHERE thattable_ID = :B1 ----- End of information for the OTHER waiting sessions ----- Information for THIS session: ----- Current SQL Statement for this session (sql_id=06sfjafxypyh6) ----- DELETE FROM thattable WHERE thattable_ID = :B1 ----- PL/SQL Stack ----- ----- PL/SQL Call Stack ----- object line object handle number name 00000003E71A8CC8 479 package body BLA.MIG 00000003E71A8CC8 511 package body BLA.MIG 00000003E1D4D348 1 anonymous block
- 28-32: the deadlock graph depicting processes/sessions and objects in the scenario
- 37-39: the weird thing, a deadlock with no rows incorporated, how come?
- 41: other ssesions wrap up, may have more that just one entry like here, regard the sql
- 58: this sessions info, sql given again, along with a pl/sql call stack
What now? Since we have a “no row deadlock” in 37-39, the deadlock appears to be schema- but not data-related. Further on, although we noticed the (current sessions) sql in the trace as of 41 and 58, the deadlock may not necessarily have happenend to the named table objects,
thattable here, but to tables below in some call stack. The most important next step is therefore to evaluate the “resource name”s given in the the deadlock graph (28-32), i.e. map these names to actual table object names as follows.
-- use the middle part of TM-0001e2cf-00000000 SQL> select object_name from user_objects where object_id = to_number('0001e2cf','xxxxxxxx'); OBJECT_NAME ---------------------------------------------------- thistable
Ok, knowing that
thistable holds a foreign key to
thattable, a concurrent
thattable from at least two sessions will concurrently lock data in
thistable. For an unindexed foreign key up to
updates to) will lock any data in
thistable completely whatsoever and its just a matter of time when locking timespans may overlap. On the other hand, just not the case here, redundant (function-based) unique key indexes is another pitfall spotted often.
Being curious to reproduce the problem in a straightforward way, I adopted and executed an example given by Tom Kyte in the article mentioned above like this (#2# identifies the second, concurrent session). Great to see, how problems become manageable (and avoidable) when there is a simple script of reproduction.
<CODE@HOST> create table p ( x int primary key ); <CODE@HOST> create table c ( x references p ); -- <CODE@HOST> create index c_idx on c(x); -- leave it == be deadlocked <CODE@HOST> insert into p select rownum from all_users where rownum <= 2; <CODE@HOST> insert into c select * from p; <CODE@HOST> commit; <CODE@HOST> select * from p; X ^^^^^^^^^^ 1 2 <CODE@HOST> select * from c; X ^^^^^^^^^^ 1 2 <CODE@HOST> delete from c where x = 1; #2# <CODE@HOST> delete from c where x = 2; #2# <CODE@HOST> delete from p where x = 2; <CODE@HOST> delete from p where x = 1; #2# delete from p where x = 2 #2# * #2# FEHLER in Zeile 1: #2# ORA-00060: Deadlock beim Warten auf Ressource festgestellt #2# <CODE@HOST> commit; -- unblock #1# <CODE@HOST> commit; <CODE@HOST> select * from p; X ^^^^^^^^^^ 2 <CODE@HOST> select * from c;