Answer
The optimizer evaluates selectivity, table size, and cost. Sequential scans are chosen for large portions of tables; bitmap scans help combine multiple indexes.
Quick Answer
PostgreSQL scan type selection: SeqScan (scan entire table - good when retrieving large % of rows), IndexScan (index lookup + heap fetch - good for selective queries), IndexOnlyScan (index only, no heap - requires covering index + all-visible pages), BitmapIndexScan + BitmapHeapScan (multiple index conditions combined, efficient for moderate selectivity). Planner chooses based on cost estimates - tune random_page_cost for SSDs.
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SugharaIQ Editorial Team
Verified Answer
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Source: SugharaIQ