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 the difference between EXPLAIN and EXPLAIN ANALYZE, and how do you read a query plan?
EXPLAIN shows the plan PostgreSQL intends to use, with estimated costs and row counts, without running the query. EXPLAIN ANALYZE actually runs the query and adds real timings and real row counts, so you can compare estimates with reality.
BeginnerIn-depth4 min read - Why do too many connections hurt PostgreSQL, and how does a connection pooler like PgBouncer help?
Each PostgreSQL connection is a separate server process with its own memory, so thousands of mostly idle connections waste RAM and add CPU overhead. A pooler like PgBouncer lets many clients share a small number of real database connections, handing a connection to a client only while it runs a transaction.
BeginnerIn-depth3 min read