How to Enable SQL Tracing for User Sessions in Oracle

Introduction
What is SQL Tracing?
Setting Up SQL Tracing Using Triggers
Example: Implementing SQL Tracing for a Specific Schema
Conclusion

Introduction

SQL tracing is a valuable tool for database administrators to diagnose performance issues, capture detailed execution plans, and collect runtime statistics of SQL statements. Automating the process of enabling and disabling SQL tracing for user sessions ensures that crucial data is collected consistently without manual intervention. In this blog post, we will explore how to use Oracle triggers to automatically start SQL tracing when a user logs on and stop it when the user logs off.

What is SQL Tracing?

SQL tracing is a diagnostic feature in Oracle that records detailed information about SQL statement execution, including:
  • Execution plans
  • Elapsed time
  • CPU time
  • Logical and physical reads
  • Wait events
This information is invaluable for identifying performance bottlenecks and optimizing SQL queries.

Setting Up SQL Tracing Using Triggers

We can use Oracle triggers to automatically enable SQL tracing at the beginning of a user session and disable it at the end. Here are the SQL scripts to create the necessary triggers:

### Create Trigger to Start SQL Tracing
The following trigger enables SQL tracing when a user logs on: 

create or replace trigger [SCHEMA_NAME]_startsqltracing
after logon on [SCHEMA_NAME].schema
begin
    execute immediate 'alter session set timed_statistics=true';
    execute immediate 'alter session set max_dump_file_size=unlimited';
    execute immediate 'alter session set events ''10046 trace name context forever, level 12''';
end;
/

### Create Trigger to Stop SQL Tracing
The following trigger disables SQL tracing when a user logs off: 

create or replace trigger [SCHEMA_NAME]_endsqltracing
before logoff on [SCHEMA_NAME].schema
begin
    execute immediate 'alter session set events ''10046 trace name context off''';
end;
/
### Drop the Triggers If you need to remove these triggers, you can use the following commands: 

drop trigger [SCHEMA_NAME]_startsqltracing;
drop trigger [SCHEMA_NAME]_endsqltracing;

Example: Implementing SQL Tracing for a Specific Schema

Let's walk through an example of implementing these triggers for a schema named `DBDOCS`.

### Step-by-Step Example:
1. **Create Start Tracing Trigger**: This trigger will enable SQL tracing when any user logs into the `DBDOCS` schema. 

create or replace trigger DBDOCS_startsqltracing
after logon on DBDOCS.schema
begin
    execute immediate 'alter session set timed_statistics=true';
    execute immediate 'alter session set max_dump_file_size=unlimited';
    execute immediate 'alter session set events ''10046 trace name context forever, level 12''';
end;
/
2. **Create Stop Tracing Trigger**: This trigger will disable SQL tracing when any user logs off from the `DBDOCS` schema. 

create or replace trigger DBDOCS_endsqltracing
before logoff on DBDOCS.schema
begin
    execute immediate 'alter session set events ''10046 trace name context off''';
end;
/
Verifying the Setup
To verify that the triggers are working correctly, follow these steps:
1. **Log In**: Log in to the `DBDOCS` schema and perform some SQL operations.
2. **Check Trace Files**: Locate the generated trace files in the `USER_DUMP_DEST` directory. These files will contain detailed information about the SQL operations performed during the session.

Removing the Triggers
If you decide to remove the triggers, use the following commands: 

drop trigger DBDOCS_startsqltracing;
drop trigger DBDOCS_endsqltracing;

Conclusion

Automating SQL tracing using triggers in Oracle Database is a powerful method to ensure detailed performance data is collected consistently. By enabling tracing when a user logs on and disabling it when they log off, DBAs can gather comprehensive insights into SQL execution without manual intervention. This practice aids in identifying performance bottlenecks and optimizing query performance, leading to a more efficient and well-tuned database environment. Implementing these triggers for SQL tracing helps maintain a high-performance database, allowing you to proactively address issues and improve overall system efficiency.

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Last updated in July, 2024

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