Monitoring PGA Usage by Username in Oracle Database

calendar Aug 21, 2025 / · 3 min read · oracle database sql memory pga dba performance tuning  ·
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Monitoring PGA Usage by Username in Oracle Database

Effective memory management is critical for Oracle Database administrators (DBAs) when diagnosing performance issues. Oracle uses the Program Global Area (PGA) for managing session memory, including operations like sorting, hashing, and storing session context. Monitoring this memory usage helps identify inefficient SQL workloads and users consuming disproportionate memory.

In this guide, we’ll break down a useful SQL script to check PGA usage by username in Oracle Database.

The SQL Script: PGA Usage by Username

 1select
 2    st.sid "SID",
 3    sn.name "TYPE",
 4    ceil(st.value / 1024 / 1024) "MB"
 5from v$sesstat st,
 6     v$statname sn
 7where st.statistic# = sn.statistic#
 8  and sid in (
 9        select sid
10        from v$session
11        where username like '&user'
12      )
13  and upper(sn.name) like '%PGA%'
14order by st.sid, st.value desc;
15/

Purpose of the Script

This script retrieves PGA memory usage for each session of a specific Oracle Database user. It allows a DBA to:

  • Track how much PGA memory (in MB) each session is consuming.
  • Identify memory-intensive users or sessions.
  • Support performance tuning by correlating heavy memory usage to SQL operations.

Breakdown of the Query

  1. Columns Selected
    • st.sid: The session ID.
    • sn.name: The type of statistic (PGA usage details).
    • ceil(st.value / 1024 / 1024) "MB": Converts raw memory usage into MB for readability.
  2. Tables/Views Used
    • v$sesstat: Holds session-level statistics.
    • v$statname: Provides names for statistics identifiers.
    • v$session: Contains active database session information.
  3. Filters Applied
    • sid in (select sid from v$session where username like '&user'): Restricts output to a specific user.
    • upper(sn.name) like '%PGA%': Filters only PGA-related statistics.
  4. Ordering
    • Ordered by SID and descending memory usage (st.value desc).

Key Points & Insights

  • Why PGA Matters: The PGA is session-private memory; unlike SGA (system shared memory), it directly affects query performance and system scalability.
  • User Focused Monitoring: By filtering by username, DBAs can identify which users are pushing PGA limits and potentially causing overall memory stress.
  • Proactive DBA Operations: This script is especially valuable in environments with mixed workloads, ensuring memory-intensive queries are quickly identified.
  • Performance Tuning Tool: If specific sessions show consistently high PGA usage, it may indicate queries needing optimization (e.g., sorts, joins, aggregations).

DBA Tips

  • Consider scheduling the script regularly to capture trends in PGA usage.
  • Use it during peak workload times to find memory bottlenecks.
  • Cross-check with workarea size policy (workarea_size_policy) and PGA aggregate target parameters.
  • Combine with AWR reports or ASH views for deeper performance insights.

Conclusion

Monitoring PGA usage by username is an essential Oracle DBA practice that ensures memory efficiency, balanced workloads, and stable system performance. By using this SQL script, administrators can quickly diagnose and address memory hotspots in the database.

References

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