How deeply does Just Use Postgres! cover bitmap?

Explains two-phase execution and exact versus lossy locations, without developing bitmap storage internals.

Bitmap

A bitmap is a compact structure that records table-row or table-page locations selected by an index condition.

A bitmap records table-row or table-page locations matching an index condition so PostgreSQL can retrieve matching data in bulk. section 4.5.2

Bitmap access proceeds in two phases:

Bitmap Index Scan finds matching index entries and records their table locations without immediately fetching rows. section 4.5.2
Bitmap Heap Scan visits the referenced table rows, reducing repeated table lookups during multi-value searches. section 4.5.2
When matches consume more memory, PostgreSQL may record whole table pages instead of individual rows, producing lossy information. section 4.5.2

Retrieving several indexed values

A query using champion_title IN (...) produces a Bitmap Index Scan followed by a Bitmap Heap Scan. The plan reports five rows and four exact heap blocks, showing how matching locations are collected before table access. section 4.5.2

SELECT username, score, level 
FROM game.player_stats 
WHERE champion_title = 'Naval Warlord';

Open the indexed lookup example, then inspect the related execution plan to see bitmap access in runnable SQL. section 4.5.2

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Geometry for ProgrammersA bitmap is a digital image represented as a grid of individually addressable pixels.

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Related concepts

bitmap heap scanused by · A bitmap heap scan reads table rows identified by a bitmap produced by an index scan and may recheck conditions for lossy pages.
continuous color functionproduces · A continuous color function maps spatial coordinates to color values while varying continuously across the image domain.
pixelhas part · A pixel is either a discrete sample carrying visual information at a position in a digital image or a reference unit used to express rendered dimensions.
bitmap index scanproduced by · A bitmap index scan is a query-plan operation that uses an index to build a bitmap of matching row locations before retrieving the corresponding table rows.
normal mappingused by · Normal mapping is a rendering technique that uses a texture to perturb surface normals without changing the underlying geometry.
vectorproduces · A vector is an ordered collection of components representing an element of a vector space.

This explainer was generated by Manning's knowledge graph from the text of Just Use Postgres!. The section links point to the parts of the book it draws on.