[Solved] This query returns false unexpectedly:SELECT pg_try_advisory_lock_shared(555);What could be the reason? | PostgreSQL

PostgreSQL - Transactions and Concurrency

This query returns false unexpectedly:

SELECT pg_try_advisory_lock_shared(555);

What could be the reason?

AThe key 555 is invalid for shared locks

BAn exclusive lock on key 555 is already held by another session

Cpg_try_advisory_lock_shared only works with transaction-level locks

DThe function requires two keys, not one

Step-by-Step Solution

Solution:

Step 1: Understand shared advisory locks behavior
Shared locks cannot be acquired if an exclusive lock on the same key is held by another session.
Step 2: Analyze why pg_try_advisory_lock_shared returns false
If an exclusive lock on key 555 exists, the shared lock attempt fails and returns false immediately.
Final Answer:
An exclusive lock on key 555 is already held by another session -> Option B
Quick Check:
Shared lock fails if exclusive lock held [OK]

Quick Trick: Shared locks fail if exclusive lock exists on key [OK]

Common Mistakes:

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This query returns false unexpectedly: