Index scan
An index scan is a database query operation that traverses an index to locate or retrieve records matching query conditions.
Just Use Postgres!
An index scan is a database access strategy that retrieves matching table rows through an index rather than examining the entire table.
- How it is used
- Diagnoses query access paths and verifies whether PostgreSQL uses indexes instead of sequential scans.
- How deep it goes
- Explains execution-plan evidence, B-tree ordering, composite-index constraints, and timing, but does not develop planner internals.
- Examples
- Uses player lookups, score ranges, leaderboards, and partitioned heart-rate aggregation queries.
- What you can do after
- Diagnose query plans with EXPLAIN and confirm whether predicates use primary-key, B-tree, composite, or partition-local indexes.
MongoDB 8.0 in Action, Third Edition
An index scan is query execution that traverses index entries to locate documents matching query conditions.
- How it is used
- Locates matching MongoDB records through index entries and helps assess whether a query avoids a collection scan.
- How deep it goes
- Explains IXSCAN in execution plans and statistics, including FETCH and covered queries, without detailing the scan’s internal algorithm.
- Examples
- Uses indexed movie-runtime queries, separately indexed $or clauses, and a covered movie projection with zero documents examined.
- What you can do after
- Diagnose/debug with explain("executionStats") to identify IXSCAN, inspect examined-key and document counts, and spot collection scans.
Read how MongoDB 8.0 in Action, Third Edition explains index scan →
PostgreSQL Mistakes and How to Avoid Them
An index scan is a query execution method that retrieves matching rows by traversing a database index.
- How it is used
- Diagnoses PostgreSQL query performance by connecting predicates, selected columns, and execution plans to index usage.
- How deep it goes
- Explains predicate matching, table reads, and plan inspection, but does not develop broader PostgreSQL planner internals.
- Examples
- Uses timestamped payments, date_trunc predicates, EXPLAIN output, expression indexes, and Python psycopg fetch comparisons.
- What you can do after
- Diagnose index use with EXPLAIN, rewrite timestamp predicates as ranges, and choose narrower projections or matching expression indexes.
Read how PostgreSQL Mistakes and How to Avoid Them explains index scan →
Related concepts
- sequential scancontrasts with · A sequential scan is a search or query operation that examines items in a table or collection in sequence to identify those matching a condition, rather than locating them through an index.
- indexinguses · Indexing is the organization or use of positions, keys, or lookup structures to identify and retrieve selected data or elements.
- composite indexused by · A composite index is a database index whose key contains multiple fields or columns, ordered according to the index definition.
- index fragmentationcontrasts with · Index fragmentation is the condition in which the logical ordering of index pages differs from their physical storage ordering or pages contain inefficiently distributed free space.
- index-only scancontrasts with · An index-only scan is a database access technique that answers a query from index contents without fetching corresponding table rows when visibility permits.
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