In Oracle, v$session, v$sql, and v$lock are key performance views used to monitor and troubleshoot the database. v$session represents all active sessions, similar to chefs in a kitchen, showing who is working and what they are waiting for. v$sql captures SQL statements being executed, like recipe cards, detailing the work each session is performing and how resource-intensive it is. v$lock monitors locks and waits, analogous to chefs waiting for shared resources like ovens or blenders. When troubleshooting, you first check v$session to see active workloads and session states. Next, you examine v$sql to identify heavy or inefficient queries affecting performance. Only then, if there are waiting sessions, you look at v$lock to find resource contention. This generalized flow—v$session → v$sql → v$lock—applies to almost any performance scenario. It ensures you understand who is active, what they are doing, and whether any are blocked. By following this order, you can quickly isolate performance issues. This approach works regardless of whether the problem is slow queries or blocked sessions.
Oracle Performance Views → Real-World Analogy
Imagine a restaurant kitchen running multiple orders simultaneously. The kitchen represents your Oracle database.
1️⃣ v$session → Who is working?
Think of v$session as the list of chefs in the kitchen.
It tells you which chef is active, what they are currently doing, and if they are waiting for something.
Example:
Chef A is chopping vegetables.
Chef B is waiting for the oven to be free.
Chef C is stirring a sauce.
SQL analogy:
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SELECT sid, username, status, sql_id, event
FROM v$session
WHERE status='ACTIVE';
Here, sid = chef ID, event = what the chef is waiting for.
2️⃣ v$sql → What task are they performing?
v$sql is like the recipe cards each chef is following.
It tells you how long a task takes, how many times it’s been executed, and which ones are heavy.
Example:
Chef A’s recipe: 10-minute salad → fast and light.
Chef B’s recipe: Baking a cake for 1 hour → resource-intensive.
Chef C’s recipe: Soup for 15 minutes → moderate.
SQL analogy:
SELECT sql_id, sql_text, executions, elapsed_time
FROM v$sql
WHERE sql_id IN (SELECT sql_id FROM v$session WHERE status='ACTIVE');
This tells you which queries (recipes) are consuming most resources.
3️⃣ v$lock → Are they waiting on someone else?
v$lock is like checking if any chef is waiting because another chef is using the same oven or blender.
Locks happen when two tasks need the same resource simultaneously.
Example:
Chef B cannot bake because Chef D is using the oven (lock).
Chef C can stir soup because they don’t need the oven (no lock).
SQL analogy:
SELECT s.sid, l.type, l.id1, l.id2, l.lmode, l.request
FROM v$lock l, v$session s
WHERE l.sid = s.sid;
Shows who is holding a resource and who is waiting.
4️⃣ Full General Flow in the Analogy
Check which chefs are active (v$session) → see workload and waits.
Check what each chef is doing (v$sql) → identify resource-heavy tasks.
Check if any chef is blocked (v$lock) → resolve contention.
By following this generalized approach, you always know:
Who is active → v$session
What’s heavy → v$sql
Who is blocked → v$lock
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