when update statemetns are running longner time

 1. Identify the SID/Session Running the UPDATE                                                                                                                                                                                                                                                                      Use SQL to locate the active session:

SELECT s.sid, s.serial#, s.username, s.status,
       s.program, q.sql_id, q.sql_text
FROM v$session s
JOIN v$sql q ON s.sql_id = q.sql_id
WHERE s.username IS NOT NULL
  AND s.sql_id = (SELECT sql_id FROM v$session WHERE sid = &your_sid);

If you don’t know the SID:

SELECT sid, serial#, sql_id, blocking_session, event, wait_class
FROM v$session
WHERE status='ACTIVE'
  AND command = 3;   -- UPDATE command

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✅ 2. Check What the Session Is Waiting On

Wait events explain why it's slow:

SELECT sid, event, wait_class, seconds_in_wait
FROM v$session
WHERE sid = &sid;

Typical causes:

• enq: TX – row lock contention → waiting for row locks

• db file sequential read / scattered read → slow IO

• buffer busy waits

• log file sync → redo/commit bottleneck

• read by other session → undo read due to consistent read

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✅ 3. Check for Blocking Sessions (Locks)

Major cause of slow updates is locking:

SELECT a.sid blocker_sid, b.sid blocked_sid, a.username blocker_user, b.username blocked_user
FROM v$session a
JOIN v$session b ON a.sid = b.blocking_session
ORDER BY a.sid;

Or:

SELECT * FROM dba_blockers;
SELECT * FROM dba_waiters;

If the update is waiting on a row lock, this will reveal the blocker.

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✅ 4. Examine Execution Plan

Look at the plan of the UPDATE's associated SELECT:

SELECT * FROM table(dbms_xplan.display_cursor('&SQL_ID'));

Check for:

• Full table scans on large tables

• Missing indexes on WHERE clause columns

• Inefficient join methods

• Filters not pushed down

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✅ 5. Check Undo & Redo Usage

Mass updates consume UNDO and REDO heavily.

Undo Retention Issues:

SELECT used_urec, used_ublk
FROM v$transaction;

Redo Log Bottleneck:

SELECT event, total_waits, time_waited
FROM v$system_event
WHERE event LIKE 'log file%';

If log file sync or log file switch is high → redo bottleneck.

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✅ 6. Check Segment Statistics

Slow due to hot blocks or high I/O:

SELECT *
FROM v$segment_statistics
WHERE owner = 'YOUR_SCHEMA'
  AND object_name = 'YOUR_TABLE'
  AND statistic_name IN ('logical reads', 'physical reads', 'buffer busy waits');

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✅ 7. Analyze Table & Index Fragmentation

Check if stats are outdated:

SELECT last_analyzed
FROM dba_tables
WHERE table_name = 'YOUR_TABLE';

If very old, gather stats:

EXEC dbms_stats.gather_table_stats('SCHEMA', 'TABLE', cascade => TRUE);

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✅ 8. Parallel Execution / TEMP Usage

Big updates may spill to TEMP:

SELECT tablespace, used_blocks, free_blocks
FROM v$temp_space_header;

Or:

SELECT sid, sql_id, temp_space_used
FROM v$sort_usage;

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✅ 9. Check AWR/ASH Reports (Best Insight)

Generate ASH report for the hour:

@$ORACLE_HOME/rdbms/admin/ashrpt.sql

Or AWR:

@$ORACLE_HOME/rdbms/admin/awrrpt.sql

Look for:

• Top SQL by elapsed time

• I/O bottlenecks

• Contention (TX lock, buffer busy, gc waits in RAC)

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✅ 10. RAC-Specific Checks (If applicable)

Check if the UPDATE is slow due to Global Cache (gc) Waits:

SELECT event FROM v$session WHERE sid = &sid;

If you see:

• gc buffer busy acquire

• gc current request

It’s a RAC hotspot issue.

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🎯 Summary: Typical Root Causes of Slow UPDATE

Cause	How to Confirm	Fix
Row lock contention	TX lock, blocking session	Kill blocker, improve app logic
Missing indexes	EXECUTION PLAN shows FTS	Add index
High I/O	Sequential/scattered reads	Tune storage, caching
Outdated stats	last_analyzed old	Gather stats
Redo bottleneck	log file sync high	Increase redo log size
RAC GC contention	gc waits	Cache affinity, partitioning
Massive undo generation	high UNDO usage	Break into batches

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If you want, I can also help you:
✅ Interpret a specific SQL_ID
✅ Read the AWR report you have
✅ Suggest index changes for the UPDATE
Just paste the SQL or SQL_ID

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