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PostgreSQL Internals & Planner

Query Planner​

Statistics​

Join Methods​

  • Nested Loop: Fast for small data sets or when using indexes on the inner table.
  • Hash Join: Most common for larger sets. Hash table built in memory.
  • Merge Join: Efficient for large, pre-sorted data sets.

Scan Methods​

  • Seq Scan: Sequential table scan.
  • Index Scan: Lookup via B-Tree/Hash etc.
  • Bitmap Scan: Combine index results (BitmapAnd/Or) before visiting heap.

Resources​