Indexing Strategy

Clustered vs Non-Clustered Index: What is the Difference?

A clustered index determines the physical order in which table rows are stored on disk, while a non-clustered index is a separate structure that stores pointer…

How Does a B-Tree Index Work Internally?

A B-tree index is a balanced, sorted tree of fixed-size nodes where every leaf sits at the same depth, letting the database find any key in O(log n) disk reads…

Hash Index vs B-Tree Index: What is the Difference?

A hash index maps each key to a bucket via a hash function, giving O(1) average-case exact-match lookups but no support for range queries or ordering, while a…

What is a Covering Index in SQL?

A covering index is an index that includes every column a query needs — both the filter/sort columns and the selected columns — so the database engine can answ…

What is a Partial Index and When Should You Use One?

A partial index is an index built over only the subset of rows that satisfy a WHERE condition, rather than every row in the table, which keeps it smaller, fast…

What is a Query Execution Plan?

A query execution plan is the step-by-step, low-level operation tree the database engine builds to actually run a SQL statement — which access paths, join orde…

What is a Reliable Methodology for Tuning a Slow SQL Query?

A reliable query-tuning methodology starts with measuring, not guessing: capture the query's actual execution plan, identify the single most expensive operatio…

What Is the Difference Between a UNIQUE Constraint and a UNIQUE Index?

A UNIQUE constraint is a schema-level rule declaring that a column or set of columns must contain no duplicate values, while a UNIQUE index is the physical dat…

How Do You Detect a Query Performance Regression?

You detect a query performance regression by continuously capturing query execution plans and timing statistics, comparing them against a historical baseline,…

What is a Global Secondary Index (GSI) in DynamoDB?

A Global Secondary Index (GSI) in DynamoDB is an alternate partition-and-sort-key view of a table that lets you query items efficiently by attributes other tha…

What is a Bitmap Index and When Should You Use One?

A bitmap index stores one bit array per distinct column value, where each bit position corresponds to a row and is set to 1 if that row holds that value, letti…

What is a B-Epsilon Tree and How Does it Differ from a B-Tree?

A B-epsilon tree (Bε-tree) is a write-optimized variant of a B-tree that attaches a message buffer to each internal node, so inserts, updates, and deletes are…