Interview Q&A / PostgreSQL
PostgreSQL interview questions
Indexes, EXPLAIN, transactions and isolation, JSONB and the Postgres specifics backend interviews probe.
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- What is MVCC in PostgreSQL, and why don't readers block writers?
MVCC (Multi-Version Concurrency Control) means PostgreSQL keeps several versions of a row. An UPDATE writes a new version instead of overwriting the old one, so a reader keeps seeing the version that was valid when its snapshot was taken while the writer works on the new one. Readers never wait for writers, and writers never wait for readers.
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