[Solved] You have the following PostgreSQL code causing a deadlock:BEGIN;LOCK TABLE orders IN ACCESS EXCLUSIVE MODE;UPDATE customers SET name = 'Alice' WHERE id = 1;-- Transaction 2 starts hereBEGIN;LOCK... | PostgreSQL

PostgreSQL - Transactions and Concurrency

You have the following PostgreSQL code causing a deadlock:

BEGIN;
LOCK TABLE orders IN ACCESS EXCLUSIVE MODE;
UPDATE customers SET name = 'Alice' WHERE id = 1;
-- Transaction 2 starts here
BEGIN;
LOCK TABLE customers IN ACCESS EXCLUSIVE MODE;
UPDATE orders SET status = 'shipped' WHERE id = 10;

What is the main issue causing the deadlock?

ATransactions lock tables in different orders causing circular wait.

BUsing SHARE MODE lock instead of EXCLUSIVE MODE.

CUpdating different tables in the same transaction.

DMissing COMMIT statements after updates.

Step-by-Step Solution

Solution:

Step 1: Analyze lock order
Transaction 1 locks orders first, then updates customers; Transaction 2 locks customers first, then updates orders.
Step 2: Identify circular wait
Each transaction waits for the other's locked table, causing deadlock due to different lock order.
Final Answer:
Transactions lock tables in different orders causing circular wait. -> Option A
Quick Check:
Different lock order = deadlock risk [OK]

Quick Trick: Lock tables in same order to avoid deadlock [OK]

Common Mistakes:

Blaming lock mode instead of order
Thinking updating different tables causes deadlock
Ignoring missing COMMIT as cause

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You have the following PostgreSQL code causing a deadlock:

Step 1: Analyze lock order

Step 2: Identify circular wait

Final Answer:

Quick Check:

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