Info: Task Oracle_87723_pr:87723 Blocked For More Than 120 Seconds.

Oracle Error ORA-87723: Task Blocked for More Than 120 Seconds - Troubleshooting and Solutions

This article dives deep into the dreaded Oracle error ORA-87723: task oracle_87723_pr:87723 blocked for more than 120 seconds. This error signifies a serious performance bottleneck in your Oracle database, indicating a task has been stalled for an excessive amount of time, severely impacting overall system responsiveness. Understanding the root cause and implementing effective solutions is crucial for maintaining database health and application performance. This guide will equip you with the knowledge and troubleshooting steps to resolve this issue.

Understanding the ORA-87723 Error

The error message explicitly states that a specific task (identified by its process ID) within the Oracle database has remained blocked for over 120 seconds. This prolonged blockage usually stems from resource contention or deadlocks. Let's break down the common culprits:

• Deadlocks: This occurs when two or more sessions are waiting for each other to release locks on resources. Imagine a scenario where Session A needs a lock held by Session B, and vice-versa – neither can proceed, resulting in a deadlock. This is a classic cause of prolonged blocking.

• Resource Contention: High contention for resources like shared memory, CPU cycles, or I/O operations can lead to extended blocking times. High load on the database, inefficient queries, or inadequate hardware can all contribute to this.

• Long-Running Transactions: Transactions that hold locks for extended periods without committing or rolling back can cause other processes to be blocked. Poorly designed database procedures or applications often contribute to this problem.

• Application Logic Errors: Flaws in the application's code that improperly handle database transactions or locks can easily trigger ORA-87723.

Troubleshooting Steps: Identifying the Root Cause

Effective troubleshooting requires a systematic approach. Here's a breakdown of the necessary steps:

1. Identify the Blocked Session

Use the following SQL query to pinpoint the sessions that are blocked:

SELECT
    s.sid,
    s.serial#,
    s.username,
    s.status,
    l.oracle_username,
    p.spid,
    l.locked_mode,
    l.object_type,
    o.object_name,
    l.blocking_session
FROM
    v$session s
JOIN
    v$lock l ON s.sid = l.sid
JOIN
    v$process p ON s.paddr = p.addr
LEFT JOIN
    dba_objects o ON l.object_id = o.object_id
WHERE
    l.blocking_session IS NOT NULL;

This query provides vital information like the session ID (SID), serial number, username, status, and the session blocking it (blocking_session). This information will be essential in the next steps.

2. Analyze the Blocking Session's Activity

Once you identify the blocking session, you need to understand what it's doing. The following queries can help:

SELECT sql_text FROM v$sql WHERE sql_id = '';  --Replace 
SELECT * FROM v$session_event WHERE sid = ; --Replace 

The first query retrieves the SQL statement executed by the blocking session. The second reveals any events the session is currently waiting on. Analyzing these will offer insights into the reason for the blockage.

3. Investigate Resource Usage

Monitor resource usage (CPU, memory, I/O) using tools like v$sysstat, v$resource_limit, and AWR (Automatic Workload Repository) reports. High utilization of any specific resource might point to a bottleneck.

4. Check for Deadlocks

Use v$session_wait and v$lock views to explicitly detect deadlocks. A deadlock situation often involves multiple sessions waiting for each other.

Solutions and Preventative Measures

Addressing ORA-87723 necessitates a multi-pronged approach:

• Kill the Blocking Session (Last Resort): If all else fails, and the blocked session is not critical, you might need to terminate it using ALTER SYSTEM KILL SESSION '<sid>,<serial#>'. However, this is a drastic step and should only be taken as a last resort, as it might lead to data inconsistency if the session was in the middle of a crucial operation.

• Optimize Queries: Inefficient queries are a major contributor. Analyze and optimize slow-running SQL statements using SQL Developer or other database tuning tools.

• Increase Resources: If resource contention is the root cause, consider upgrading hardware (CPU, memory, I/O) or increasing the database instance's resources.

• Improve Application Design: Ensure the application's database interaction is optimized. Use proper transaction management, avoid long-running transactions, and implement appropriate locking mechanisms.

• Regular Monitoring: Implement proactive monitoring using tools that alert you to potential performance issues before they escalate into ORA-87723 errors.

By systematically following these troubleshooting steps and implementing preventative measures, you can effectively eliminate ORA-87723 errors and maintain the optimal performance of your Oracle database. Remember to always back up your data before making any significant changes to the database configuration or schema.