Postgresql medium
What is the behavior of the default transaction isolation level in PostgreSQL when multiple clients are accessing the same data?
- A Serializable: Ensures total ordering as if all database transactions ran sequentially.
- B Read Committed: A query only sees data that was committed before the query started.
- C Repeatable Read: Ensures that a query sees a snapshot of the database at start time.
- D Read Uncommitted: Allows for 'Dirty Reads' where uncommitted data is visible to others.
Answer: B. Read Committed: A query only sees data that was committed before the query started.
PostgreSQL defaults to 'Read Committed'. This prevents 'Dirty Reads' but allows 'Non-Repeatable Reads' (where a value might change if read twice in one transaction). Interestingly, PG treats 'Read Uncommitted' identically to 'Read Committed'.
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