Blog List

• June 2026 (1)
  
  1. One Case of DBMS_ALERT deadlock
• April 2026 (1)
  
  1. One Oracle TDE Performance Test
• January 2026 (4)
  
  1. Oracle ORA-01426: numeric overflow and PL/SQL Runtime MCODE
  2. Oracle SQL MEMBER vs. IN Comparison Condition Performance - Part1
  3. Oracle SQL MEMBER vs. IN Comparison Condition Performance - Part2
  4. "Disk file operations I/O" with (FileOperation: 8, fileno: 0, filetype: 8) Test
• December 2025 (1)
  
  1. Three Oracle cursor error Tests
• September 2025 (3)
  
  1. ORA-06502: NULL index table key value and plsql_optimize_level
  2. "ORA-00001: unique constraint violated" Debugging
  3. Oracle Database Stuck on DB Writer Wait Event: "oradebug request completion"
• August 2025 (1)
  
  1. Reading CLOB Line by Line with SQL and Plsql: ChatGPT and Gemini Implementations
• July 2025 (3)
  
  1. Reading CLOB Line by Line with SQL and Plsql
  2. "library cache: bucket mutex X" on V$ Fixed Views: Case Test
  3. Oracle dbms_hprof: Uncatchable Time in PL/SQL Nested Program Units
• June 2025 (1)
  
  1. ORA-01002: fetch out of sequence: One Case Test
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  1. Oracle ORA-00600 [pfrsfm: stack mismatch] and [pfrsfm: stack mismatch] Reproducing
• February 2025 (1)
  
  1. One Oracle CLOB Space Usage Test
• November 2024 (1)
  
  1. Oracle Self-tune checkpointing lag of log switch
• October 2024 (1)
  
  1. Find the skipped rows in select for update skip locked
• September 2024 (1)
  
  1. One OracleJVM TIME_MODEL Test
• April 2024 (3)
  
  1. Oracle AQ Dequeue 'KTC latch subh' Memory Leak and Dequeue Long Running Test
  2. One Test of Oracle Object Collection MEMBER OF Function
  3. In Memoriam of Prof. Niklaus Wirth: One Email on Program Debugging
• January 2024 (1)
  
  1. One Test on the Different Errors of Oracle Global Temporary Tables vs. Private Temporary Tables
• October 2023 (1)
  
  1. ORA-28268: Exceeded the maximum allowed size for Context information in a session
• September 2023 (3)
  
  1. Oracle Index Root Modification CBC Latch Contention: Workaround Studies
  2. Oracle 19.18 Wait Event 'latch: cache buffers chains' P3: block number
  3. Oracle Index Range Scan with LIKE Condition on Wildcard '_'
• August 2023 (1)
  
  1. Oracle SYS_GUID Composition
• June 2023 (1)
  
  1. One Deadlock of 'row cache lock' and 'library cache lock'
• April 2023 (3)
  
  1. Oracle Multi-Consumer AQ dequeue with dbms_aq.listen Wait Events (I)
  2. Oracle Multi-Consumer AQ dequeue with dbms_aq.listen Performance Model (II)
  3. Oracle Multi-Consumer AQ dequeue with dbms_aq.listen Performance Analysis and Workaround (III)
• March 2023 (2)
  
  1. One Test of Oracle JSON Plsql PGA Memory Leak
  2. One Test of ORA-00600: [KGL-heap-size-exceeded] With AQ Subscriber
• February 2023 (1)
  
  1. Oracle Scalar Subquery Caching and Non-deterministic Functions
• January 2023 (1)
  
  1. Oracle dbms_crypto.randombytes and Enhancement Suggestion
• December 2022 (2)
  
  1. OracleJVM JAVA_JIT_ENABLED Linux /dev/shm mount noexec EPERM and Performance
  2. One Test of Oracle too many parse errors with ORA-12850 and ORA-12872
• October 2022 (2)
  
  1. How many times SYSDATE is called in SQL and Plsql ?
  2. Oracle WITH subquery_factoring_clause TEMP TABLE TRANSFORMATION and log file sync
• September 2022 (2)
  
  1. Update Restart and Undo Extends
  2. Proposal for ORA-04030 incident/trace files Enhancement to list Plsql package Memory Usage
• August 2022 (2)
  
  1. Oracle Global Temporary Table ORA-01555 and Undo Retention
  2. Oracle Global Temporary Table ORA-01555 and XML Data Size
• July 2022 (1)
  
  1. Plsql ORA-00600 by JDBC Call Exception Catch
• June 2022 (1)
  
  1. Tests of Oracle ORA-01866: the datetime class is invalid
• May 2022 (2)
  
  1. How volatile is ORA-00600 [qernsRowP] ?
  2. One Case of ORA-00036: Maximum Number Of Recursive SQL Levels (50) Exceeded
• April 2022 (2)
  
  1. Oracle Write Consistency and ORA-30926: "unable to get a stable set of rows in the source tables"
  2. Oracle Write Consistency and ORA-00600: [13030], [20]
• March 2022 (1)
  
  1. Index Skip Scan With First Column of Composite Index Specified
• February 2022 (2)
  
  1. Oracle Kill Session Crashes DB Instance
  2. How to determine session's CURRVAL of an oracle sequence without error and without modify ?
• January 2022 (1)
  
  1. Oracle SQL Monitoring Shared Pool "keomg: entry list " Memory Leak
• December 2021 (1)
  
  1. How to count the inserts and updates from merge ?
• November 2021 (1)
  
  1. Oracle dbms_aq.dequeue_array Shared Pool "KTC Latch Subh" Memory Leak
• October 2021 (2)
  
  1. Oracle Temp Space Usage Monitoring and View v$tempseg_usage
  2. Oracle sessiontimezone Format Changed After Calling dbms_scheduler/dbms_job Subprograms
• July 2021 (1)
  
  1. Oracle Program and Table dc_objects "row cache lock"
• June 2021 (1)
  
  1. Oracle dbms_alert and its Wait Events
• May 2021 (1)
  
  1. Oracle 19c new shared pool "SO private sga" and "SO private so latch" Performance Impacts
• April 2021 (3)
  
  1. Oracle PLITBLM "library cache: mutex X"
  2. The Third Test of ORA-04025: maximum allowed library object lock
  3. Oracle forall DML save exceptions and ORA-04030: out of process memory (callheap,psdalf:RPI allocations)
• March 2021 (2)
  
  1. Oracle Temp File Read Time Stats Problem
  2. Oracle deallocate_unused_clause and its effect
• January 2021 (1)
  
  1. DBMS_SCHEDULER Job Not Running and Used Slaves
• November 2020 (3)
  
  1. OracleJVM integer Array Size Limit and Out of Memory Error
  2. Oracle LOB Chunksize and Buffersize
  3. One case of dbms_alert.signal deadlock
• September 2020 (1)
  
  1. The Second Test of ORA-600 [4156] Rolling Back To Savepoint
• August 2020 (1)
  
  1. Row Cache Object and Row Cache Mutex Case Study
• May 2020 (3)
  
  1. 12cR2 Index Usage Tracking Manual Flushing
  2. One "row cache lock" Test Case
  3. ORA-600 [504] LATCH HIERARCHY ERROR Deadlock
• April 2020 (3)
  
  1. Index Service ITL and Recursive Transaction
  2. Index Block Split Point Distribution
  3. Cache Buffer Chains Latch Contention Case Study-3: index root block Modification Blocking
• February 2020 (2)
  
  1. Cache Buffer Chains Latch Contention Case Study-2: Reverse Primary Key Index
  2. Cache Buffer Chains Latch Contention Case Study-1: Reverse Key Index
• January 2020 (1)
  
  1. Oracle Unique Index Non-Consistency Read with RowCR
• December 2019 (2)
  
  1. Oracle Database and Java Datetime Conversion Differences across Daylight Saving Time (DST)
  2. Oracle 19.4 OracleJVM JAVA_JIT_ENABLED Not Working on AIX
• August 2019 (2)
  
  1. Oracle 18 New Wait Event: 'index (re)build lock or pin object'
  2. PDML Disabled on Nonpartitioned IOT
• April 2019 (1)
  
  1. LOB ORA-22924: snapshot too old and Fix
• November 2018 (5)
  
  1. Oracle row cache objects Event: 10222, Dtrace Script (I)
  2. Row Cache Objects, Row Cache Latch on Object Type: Plsql vs Java Call (Part-1) (II)
  3. Row Cache Objects, Row Cache Latch on Object Type: Plsql vs Java Call (Part-2) (III)
  4. Row Cache and Sql Executions (IV)
  5. Latch: row cache objects Contentions and Scalability (V)
• October 2018 (2)
  
  1. Oracle ROWCACHE Views and Contents
  2. Result Cache: RC Enqueue and Contention (V)
• July 2018 (3)
  
  1. row cache mutex in Oracle 12.2.0.1.0
  2. plshprof command-line utility in Oracle 12.2.0.1.0
  3. 12c Online Statistics Gathering for Direct Path Insert and 3 Side Effects
• April 2018 (1)
  
  1. TM Lock and No Transaction Commit, TX & TM Locks and No Transaction Visible
• March 2018 (2)
  
  1. 'enq: RO - fast object reuse' and 'enq: KO - fast object checkpoint' Final Blocker
  2. Oracle 12.1 Wait Event: 'log file sync: SCN ordering' Demo
• February 2018 (1)
  
  1. SYS.LOADER_DIR_OBJS Query: Privileges and Performance
• January 2018 (4)
  
  1. Oracle Logical Read: Current Gets Access Path and Cost
  2. Oracle Logical Read: Consistent Gets Access Path and Cost
  3. Oracle Physical Read Access Path and Cost
  4. Oracle Latch Misses, Spin_gets, Sleeps and Recurrent_Misses
• October 2017 (2)
  
  1. ORA-04025 library object lock on DATABASE Truncate Triggers
  2. Result Cache: 0 rows updated Invalidations (IV)
• September 2017 (2)
  
  1. Result Cache: RC Latch Contention and PL/SQL Exception Handler (III)
  2. Result Cache: RC Latch Contention and RESULT_CACHE_MAX_SIZE(II)
• July 2017 (3)
  
  1. nls_database_parameters, dc_props, latch: row cache objects
  2. v$database select and control file sequential read
  3. Getting Oracle Transaction Commit SCN
• May 2017 (8)
  
  1. JDBC, Oracle object/collection, dbms_pickler, NOPARALLEL sys.type$ query
  2. PLSQL Context Switch Functions and Cost
  
  
  3. Oracle Datetime (1) - Concepts
  4. Oracle Datetime (2) - Examples
  5. Oracle Datetime (3) - Assignments
  6. Oracle Datetime (4) - Comparisons
  7. Oracle Datetime (5) - SQL Arithmetic
  8. Oracle Datetime (6) - PLSQL Arithmetic
• March 2017 (3)
  
  1. Oracle 12c PL/SQL Function in the WITH Clause: wrong result
  2. Oracle abstract_lob Memory Leak
  3. PL/SQL Function Result Cache Invalidation (I)
• February 2017 (1)
  
  1. Oracle JVM Java OutOfMemoryError and lazy GC
• January 2017 (1)
  
  1. ORA-600 [4156] SAVEPOINT and PL/SQL Exception Handling
• November 2016 (1)
  
  1. "library cache: mutex X" and Application Context
• September 2016 (2)
  
  1. PL/SQL Multidimensional Collection Memory Usage and Performance
  1. dbms_session.get_package_memory_utilization and limitations
• August 2016 (1)
  
  1. ORA-04025 library object lock on AQ queue and SQL cursor
• June 2016 (1)
  
  1. SQL Parsing in serializable transaction throws ORA-08177: can't serialize access for this transaction
• May 2016 (1)
  
  1. Oracle Fixed Table Practice
• April 2016 (1)
  
  1. sql_id and idn to shared pool subpool
• February 2016 (1)
  
  1. Native Code Files: Ora-7445 [Ioc_pin_shared_executable_object()] Reproducing
• January 2016 (3)
  
  1. Performance of Oracle Object Collection Comparisons - Part2
  2. Performance of Oracle Object Collection Comparisons - Part1
  3. Foreign Keys and Library Cache Locks: Analysis
• December 2015 (1)
  
  1. Oracle bigfile tablespace pre-allocation and session blocking
• November 2015 (1)
  
  1. Oracle 12c single session "library cache lock (cycle)" deadlock
• September 2015 (2)
  
  1. SQL DML Exceptions, Rollbacks and PL/SQL Exception Handlers
  2. Limit PGA Memory Usage
• August 2015 (1)
  
  1. Latch _SPIN_COUNT: adaptive
• July 2015 (2)
  
  1. Redo Practice
  2. UNDO Practice
• June 2015 (1)
  
  1. Temporary LOB Memory Allocation and Freeing in JAVA
• April 2015 (2)
  
  1. IBM AIX POWER7 CPU Usage and Throughput
  2. Oracle 11.2.0.4.0 AWR "Tablespace IO Stats" Column Names Shifted
• January 2015 (1)
  
  1. open_cursors, session_cached_cursors: cursordump
• December 2014 (1)
  
  1. Local prefixed vs. nonprefixed indexes: Column Null Values
• November 2014 (2)
  
  1. reverse key index: the remedy is worse than the symptoms
  2. Low High Water Mark, High High Water Mark, and Parallel Query
• May 2014 (3)
  
  1. Oracle 11g AUTO_SAMPLE_SIZE performance on Small Tables
  2. java stored procedure calls and latch: row cache objects, and performance
  3. java stored procedure calls and latch: row cache objects
• March 2014 (2)
  
  1. dbms_aq.dequeue - latch: row cache objects on AIX
  2. Hot Block Identification and latch: cache buffers chains
• November 2013 (3)
  
  1. Remove Stale Native Code Files on AIX
  2. PGA, SGA memory usage watching from UNIX
  3. ORA-04030 incident file and alert.log
• September 2013 (1)
  
  1. Execution Switching between "direct path read" and "db file scattered read"
• June 2013 (2)
  
  1. Oracle PL/SQL Collection Memory Reclaim 
  2. dbms_alert lock hash collision
• April 2013 (2)
  
  1. cursor: pin S wait on X
  2. Shared Pool - Free Memory, Fragmentation ?
• March 2013 (3)
  
  1. Shared Pool - SQLA and KGLH0
  2. Shared Pool - Memory Allocation - unbalanced
  3. Shared Pool - KKSSP
• December 2012 (1)
  
  1. Delete Restart and new Active Undo Extent
• November 2012 (2)
  
  1. One Oracle AQ Deadlock
  2. Oracle Java OutOfMemoryError
• July 2012 (1)
  
  1. One Mutex Collision Test
• May 2012 (1)
  
  1. Why shared pool is doubled ?
• April 2012 (1)
  
  1. High system time utilization on fast machine
• February 2012 (1)
  
  1. Is latch misses statistic gathered or deduced ?
• November 2011 (2)
  
  1. One Oracle 12g Pre-announce of bug fix in dbms_debug_jdwp
  2. Oracle 11gR2 single session "library cache pin"
• July 2011 (1)
  
  1. Redo/Undo explosion from thick declared table insert
• May 2011 (3)
  
  1. ORA-04027: self-deadlock during automatic validation
  2. Foreign Key on Nested Table
  3. Update Restart and new Active Undo Extent
• April 2011 (1)
  
  1. dbms_session package_memory_utilization

One Case of DBMS_ALERT deadlock

In this Blog, we will demonstrate a test case of DBMS_ALERT deadlock.

Note: Tested in Oracle 19c

Open two Sqplus sessions: SESS-1 and SESS-2.

1. At T1, login to SESS-1, register two alert interests: alert_1 and alert_2, then exit the session:

exec dbms_alert.register('alert_1');

exec dbms_alert.register('alert_2');

exit;

2. At T2, re-login to SESS-1 (sid: 552), check two registered names:

-- watch two registered names, whose session is not alive.

select * from sys.dbms_alert_info where name like 'ALERT%';

NAME            SID             CHANGED    MESSAGE
--------------- --------------- ---------- ---------------
ALERT_1         0228CD530001    N
ALERT_2         0228CD530001    N

-- determines if the specified session is active.
declare
  l_unique_sid varchar2(30) := '0228CD530001';
begin
  if not dbms_session.is_session_alive(l_unique_sid) then
    dbms_output.put_line('Not Alive: (sid: ' ||to_number(substr(l_unique_sid, 1, 4), 'XXXX')||
                                ', serial#: '||to_number(substr(l_unique_sid, 5, 4), 'XXXX')||
                                   ', inst: '||to_number(substr(l_unique_sid, 9, 4), 'XXXX')||')');
  end if;
end;
/

Not Alive: (sid: 552, serial#: 52563, inst: 1)

3. At T3, continue in SESS-1, send signal: alert_2

SQL (sid:552) > exec dbms_alert.signal('alert_2', 'alert_msg_2');

4. At T4, login to SESS-2 (sid: 16), register one alert interests: alert_3

SQL (sid:16) > exec dbms_alert.register('alert_3');

--Note that this call is with default cleanup = true to perform cleanup of any extant orphaned pipes.

5. At T5, in SESS-1, check TX lock, SESS-2 (sid:16) is blocked by SESS-1 (sid: 552)

SQL (sid:552) > select * from  v$lock where type = 'TX';

ADDR             KADDR             SID TY        ID1        ID2      LMODE    REQUEST      CTIME      BLOCK     CON_ID
---------------- ---------------- ---- -- ---------- ---------- ---------- ---------- ---------- ---------- ----------
00000000B4310970 00000000B43109A0   16 TX    5505024     782554          0          6        132          0          0
00000000ADB30E70 00000000ADB30EA8  552 TX    5505024     782554          6          0        169          1          0
00000000ADBCFAB8 00000000ADBCFAF0   16 TX    6291482     236621          6          0        132          0          0

3 rows selected.

6. At T6, in SESS-1, send signal: alert_1

SQL (sid:552) > exec dbms_alert.signal('alert_1', 'alert_msg_1');

7. Both sessions throw ORA-00060

SQL (sid:16) > exec dbms_alert.register('alert_3');
BEGIN dbms_alert.register('alert_3'); END;

*
ERROR at line 1:
ORA-00060: deadlock detected while waiting for resource
ORA-06512: at "SYS.DBMS_ALERT", line 82
ORA-06512: at "SYS.DBMS_ALERT", line 82
ORA-06512: at "SYS.DBMS_ALERT", line 103
ORA-06512: at line 1

SQL (sid:552) > exec dbms_alert.signal('alert_1', 'alert_msg_1');
BEGIN dbms_alert.signal('alert_1', 'alert_msg_1'); END;

*
ERROR at line 1:
ORA-00060: deadlock detected while waiting for resource
ORA-06512: at "SYS.DBMS_ALERT", line 431
ORA-06512: at line 1

8. Both Deadlock trc files:

=================== testdb_ora_1851008.trc ===================

Unix process pid: 1851008, image: oracle@testdb

*** SESSION ID:(16.33150) 2026-06-09T15:35:47.444358+02:00
 
Deadlock graph:
                                          ------------Blocker(s)-----------  ------------Waiter(s)------------
Resource Name                             process session holds waits serial  process session holds waits serial
TX-0060001A-00039C4D-00000000-00000000         66      16     X        33150      63     552           X  57779
TX-00540000-000BF0DA-00000000-00000000         63     552     X        57779      66      16           X  33150
 
----- Information for waiting sessions -----
Session 16:
Holds resource TX-0060001A-00039C4D-00000000-00000000 acquired 204 seconds ago.
  sid: 16 ser: 33150 audsid: 131915016 user: 0/SYS
    flags: (0x41) USR/- flags2: (0x40009) -/-/INC
    flags_idl: (0x1) status: BSY/-/-/- kill: -/-/-/-
  pid: 66 O/S info: user: oracle, term: UNKNOWN, ospid: 1851008
    image: oracle@testdb
  client details:
    O/S info: user: U000380, term: WCLINBDOXKKDUGS, ospid: 42636:42136
    machine: SYS\WCLINBDOXKKDUGS program: sqlplus.exe
    application name: SQL*Plus, hash value=3669949024
  current SQL:
  DELETE DBMS_ALERT_INFO WHERE SID = :B1 
 
Session 552:
Holds resource TX-00540000-000BF0DA-00000000-00000000 acquired 241 seconds ago.
  sid: 552 ser: 57779 audsid: 131915017 user: 0/SYS
    flags: (0x41) USR/- flags2: (0x40009) -/-/INC
    flags_idl: (0x1) status: BSY/-/-/- kill: -/-/-/-
  pid: 63 O/S info: user: oracle, term: UNKNOWN, ospid: 1851016
    image: oracle@testdb
  client details:
    O/S info: user: U000380, term: WCLINBDOXKKDUGS, ospid: 57408:55064
    machine: SYS\WCLINBDOXKKDUGS program: sqlplus.exe
    application name: SQL*Plus, hash value=3669949024
  current SQL:
  UPDATE DBMS_ALERT_INFO SET CHANGED = 'Y', MESSAGE = :B2 WHERE NAME = UPPER(:B1 )


session 16: DID 0001-0042-0000011E	session 552: DID 0001-003F-000005CF 
session 552: DID 0001-003F-000005CF	session 16: DID 0001-0042-0000011E 
 
Rows waited on:
  Session 16: obj - rowid = 003C067C - AAPAZ8AG+AAAXuhAAC
  (dictionary objn - 3933820, file - 446, block - 97185, slot - 2)
  Session 552: obj - rowid = 003C067C - AAPAZ8AG+AAAXuhAAB
  (dictionary objn - 3933820, file - 446, block - 97185, slot - 1)

=================== testdb_ora_1851016.trc ===================

Unix process pid: 1851016, image: oracle@testdb

*** SESSION ID:(552.57779) 2026-06-09T15:35:50.836313+02:00

Deadlock graph:
                                          ------------Blocker(s)-----------  ------------Waiter(s)------------
Resource Name                             process session holds waits serial  process session holds waits serial
TX-00540000-000BF0DA-00000000-00000000         63     552     X        57779      61     196           X   9237
TX-005B0001-000BE24C-00000000-00000000         61     196     X         9237      63     552           X  57779
 
----- Information for waiting sessions -----
Session 552:
Holds resource TX-00540000-000BF0DA-00000000-00000000 acquired 245 seconds ago.
  sid: 552 ser: 57779 audsid: 131915017 user: 0/SYS
    flags: (0x41) USR/- flags2: (0x40009) -/-/INC
    flags_idl: (0x1) status: BSY/-/-/- kill: -/-/-/-
  pid: 63 O/S info: user: oracle, term: UNKNOWN, ospid: 1851016
    image: oracle@testdb
  client details:
    O/S info: user: U000380, term: WCLINBDOXKKDUGS, ospid: 57408:55064
    machine: SYS\WCLINBDOXKKDUGS program: sqlplus.exe
    application name: SQL*Plus, hash value=3669949024
  current SQL:
  UPDATE DBMS_ALERT_INFO SET CHANGED = 'Y', MESSAGE = :B2 WHERE NAME = UPPER(:B1 )
 
Session 196:
Holds resource TX-005B0001-000BE24C-00000000-00000000 acquired 3 seconds ago.
  sid: 196 ser: 9237 audsid: 131915018 user: 0/SYS
    flags: (0x10041) USR/- flags2: (0x40009) -/-/INC
    flags_idl: (0x1) status: BSY/-/-/- kill: -/-/-/-
  pid: 61 O/S info: user: oracle, term: UNKNOWN, ospid: 1850047
    image: oracle@testdb (J006)
  client details:
    O/S info: user: oracle, term: UNKNOWN, ospid: 1850047
    machine: testdb program: oracle@testdb (J006)
    application name: task-911-2 hash value=1117638710
    action name: bgp: loop: init, hash value=2828460256
  current SQL:
  DELETE DBMS_ALERT_INFO WHERE SID = :B1 
 

session 552: DID 0001-003F-000005CF	session 196: DID 0001-003D-000004C1 
session 196: DID 0001-003D-000004C1	session 552: DID 0001-003F-000005CF 
 
Rows waited on:
  Session 552: obj - rowid = 003C067C - AAPAZ8AG+AAAXuhAAB
  (dictionary objn - 3933820, file - 446, block - 97185, slot - 1)
  Session 196: obj - rowid = 003C067C - AAPAZ8AG+AAAXuhAAC
  (dictionary objn - 3933820, file - 446, block - 97185, slot - 2)

9. Repeat Test

To repeat test, exit both SESS-1 and SESS-2, open a third SESS-3, and register a new alert to cleanup alert_1, alert_2, alert_3. Then repeat above test steps.

exec dbms_alert.register('alert_other');

10. Reasoning

Two alert interests are inserted (registered) into sys.dbms_alert_info in the order of alert_1 and alert_2, both with the same unique_session_id: 0228CD530001.

When we register alert interest: alert_3, DBMS_ALERT first performs cleanup of not alive sessions by delete in default order: alert_1 and alert_2.

Whereas we frist send (update) signal: alert_2, then alert_1.

In this case, Updates vs Delete are interfered in crossing row order, hence Deadlock.