> Term
Database Statistics
Data about table sizes, row distributions, and index compositions used by the query optimizer to plan execution paths.
Detailed Explanation
Database statistics provide the query planner with metadata about the underlying data. This includes row counts, data distribution (histograms), and the number of distinct values in columns.
The optimizer relies on these stats to decide whether to use an index scan, a sequential scan, or specific join strategies. If stats are outdated, the database might choose a catastrophically inefficient query plan.
Why It Matters
Prevents the query planner from making terrible execution decisions, like doing a full table scan on a massive table because it thought there were only 10 rows.
Common Failure Mode
Practical Example
Production Manifestation
Background processes like `ANALYZE` in PostgreSQL or `UPDATE STATISTICS` in SQL Server.
Frequently Asked Questions
What is Database Statistics in short?
Data about table sizes, row distributions, and index compositions used by the query optimizer to plan execution paths.
What is the most common failure mode?
A massive bulk data insert occurs, but statistics aren't updated. The query optimizer still thinks the table is empty and chooses a terrible execution plan, causing an outage.
AI Summary
Data about table sizes, row distributions, and index compositions used by the query optimizer to plan execution paths. Prevents the query planner from making terrible execution decisions, like doing a full table scan on a massive table because it thought there were only 10 rows.