Cookbook recipe

Isolation levels in plain terms

Applies to PostgreSQL 13–17 Last reviewed May 2026 Grounded in source

What This Is

A production experience capsule based on real incident patterns.

Why It Matters

Builds production judgment under pressure.

Next Step

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Estimated investigation4 min

Scenario

Read Committed, Repeatable Read, Serializable — they sound abstract until a concurrency bug bites. Here is what each actually guarantees. Diagnose it Set the level for a transaction: BEGIN ISOLATION LEVEL REPEATABLE READ; -- ... statements…

Investigation Path

Read Committed, Repeatable Read, Serializable — they sound abstract until a concurrency bug bites. Here is what each actually guarantees.

Diagnose it

Set the level for a transaction:

BEGIN ISOLATION LEVEL REPEATABLE READ;
-- ... statements see one consistent snapshot ...
COMMIT;

Why it happens

Read Committed (default) takes a fresh snapshot per statement, so two reads can differ. Repeatable Read freezes one snapshot for the whole transaction. Serializable adds detection so concurrent transactions behave as if run one at a time.

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Career Impact

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Related & next steps

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Concepts on this page

Isolation level Transaction Deadlock
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