1---
2title: Keep Transactions Short to Reduce Lock Contention
3impact: MEDIUM-HIGH
4impactDescription: 3-5x throughput improvement, fewer deadlocks
5tags: transactions, locking, contention, performance
6---
7 
8## Keep Transactions Short to Reduce Lock Contention
9 
10Long-running transactions hold locks that block other queries. Keep transactions as short as possible.
11 
12**Incorrect (long transaction with external calls):**
13 
14```sql
15begin;
16select * from orders where id = 1 for update;  -- Lock acquired
17 
18-- Application makes HTTP call to payment API (2-5 seconds)
19-- Other queries on this row are blocked!
20 
21update orders set status = 'paid' where id = 1;
22commit;  -- Lock held for entire duration
23```
24 
25**Correct (minimal transaction scope):**
26 
27```sql
28-- Validate data and call APIs outside transaction
29-- Application: response = await paymentAPI.charge(...)
30 
31-- Only hold lock for the actual update
32begin;
33update orders
34set status = 'paid', payment_id = $1
35where id = $2 and status = 'pending'
36returning *;
37commit;  -- Lock held for milliseconds
38```
39 
40Use `statement_timeout` to prevent runaway transactions:
41 
42```sql
43-- Abort queries running longer than 30 seconds
44set statement_timeout = '30s';
45 
46-- Or per-session
47set local statement_timeout = '5s';
48```
49 
50Reference: [Transaction Management](https://www.postgresql.org/docs/current/tutorial-transactions.html)
51