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Oracle ORA-02080 Error: Causes and Solutions Complete Guide

#oracle #database #dba #sql

ORA-02080: Database Link Is In Use — Causes, Fixes & Prevention

ORA-02080 occurs when you attempt to drop or modify a database link (DB Link) that is currently being used by one or more active sessions. Oracle marks a DB Link as "in use" as soon as a session opens a connection through it to a remote database, and it stays in that state until the session explicitly closes the link or the session itself is terminated. This error is common during maintenance windows when DBAs attempt to clean up or reconfigure DB Links without checking for active usage first.

Top 3 Causes

1. Active Session Using the DB Link

The most common cause — a session is currently querying a remote database through the DB Link, or an open transaction is holding the link open.

-- Find sessions currently using a DB Link
SELECT
    s.sid,
    s.serial#,
    s.username,
    s.status,
    s.machine,
    d.db_link,
    d.logged_on
FROM
    v$session s,
    v$dblink d
WHERE
    s.saddr = d.session_addr;
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2. Uncommitted Distributed Transaction Holding the Link

After a DML operation (INSERT/UPDATE/DELETE) over a DB Link, if the application fails to issue a COMMIT or ROLLBACK, the distributed transaction keeps the link open indefinitely.

-- Check for in-doubt distributed transactions
SELECT
    local_tran_id,
    global_tran_id,
    state,
    advice
FROM
    dba_2pc_pending;

-- Force commit or rollback if necessary (verify data integrity first!)
COMMIT FORCE '1.22.135';
-- or
ROLLBACK FORCE '1.22.135';
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3. Scheduled Job or Batch Process Actively Using the Link

A DBMS_SCHEDULER job or background batch process may be executing queries through the DB Link at the exact time you attempt the DDL operation.

-- Check running scheduler jobs that may use the DB Link
SELECT
    job_name,
    state,
    last_start_date,
    next_run_date
FROM
    dba_scheduler_jobs
WHERE
    state = 'RUNNING';
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Quick Fix Solutions

Step 1 — Identify and kill the blocking session:

-- Kill the session holding the DB Link open
ALTER SYSTEM KILL SESSION 'SID,SERIAL#' IMMEDIATE;

-- Example
ALTER SYSTEM KILL SESSION '145,23891' IMMEDIATE;
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Step 2 — Retry the DROP after sessions are cleared:

-- Drop a private DB Link
DROP DATABASE LINK your_db_link_name;

-- Drop a public DB Link
DROP PUBLIC DATABASE LINK your_db_link_name;
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Step 3 — If the session won't die, find the OS process:

-- Get OS-level PID for forced termination
SELECT s.sid, s.serial#, p.spid AS os_pid
FROM v$session s
JOIN v$process p ON s.paddr = p.addr
WHERE s.sid = 145;  -- replace with actual SID
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Prevention Tips

1. Always COMMIT or ROLLBACK after DB Link operations in your application code.
Make it a coding standard that every code path — including exception handlers — explicitly terminates any transaction that involves a DB Link. This prevents orphaned distributed transactions from blocking future maintenance.

2. Run a pre-check query before any DB Link DDL operation.
Add this check to your change management runbook so it becomes a mandatory step before dropping or altering any DB Link in production:

-- Pre-maintenance DB Link usage check
SELECT
    d.db_link,
    s.sid,
    s.serial#,
    s.username,
    s.logon_time,
    ROUND((SYSDATE - s.logon_time) * 24 * 60, 1) AS minutes_connected
FROM
    v$dblink d
JOIN
    v$session s ON d.session_addr = s.saddr
ORDER BY
    minutes_connected DESC;
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If this query returns any rows for your target DB Link, coordinate with the application team to release the connection before proceeding with your DDL.

Related Errors

  • ORA-02081 — database link is not open
  • ORA-01017 — invalid username/password (common after DB Link recreation)
  • ORA-12154 — TNS could not resolve connect identifier
  • ORA-02049 — timeout: distributed transaction waiting for lock

📖 Want a more detailed guide?
Check out the full in-depth version (Korean) on oraerror.com — includes detailed analysis, additional SQL examples, and prevention tips.

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