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CQL for DSE

  • Overview
    • Cassandra structure
    • About CQL
    • CQL quick reference
    • Known issues
  • Getting started
    • Vector Search Quickstart
    • CQL Quickstart
    • SAI Quickstart
    • DSE Search Indexing Quick Start
  • Planning
    • Data modeling
      • Data modeling concepts
      • Data modeling analysis
  • Connecting
    • cqlsh (startup options)
      • Accessing data using CQL
        • Starting the standalone cqlsh tool
        • Starting cqlsh
    • Developing
      • Introduction to CQL
      • Managing keyspaces
        • Keyspace concepts
        • Create a keyspace
        • Check a keyspace
        • Alter a keyspace
        • Drop a keyspace
      • Managing tables
        • Table concepts
        • Data types
        • Create a table
        • Check a table
        • Alter a table
        • Truncate a table
        • Drop a table
      • Managing columns
        • Managing columns
        • Create a table column
        • Check column existence
        • Alter a table column
        • Drop a column
        • User-defined type (UDT) overview
          • Create a user-defined type (UDT)
          • Check for user-defined type (UDT) existence
          • Alter a user-defined type (UDT)
          • Drop a user-defined type (UDT)
        • User-defined functions (UDFs) and user-defined aggregates (UDAs) overview
          • Create a user-defined function (UDF)
          • Check a user-defined function (UDF)
          • Drop a user-defined function (UDF)
          • Create a user-defined aggregate function (UDA)
          • Checking a user-defined aggregate (UDA)
          • Drop a user-defined aggregate (UDA)
      • Managing Materialized views
        • Materialized views concepts
        • Known limitations of materialized views
        • Create a materialized view (MV)
        • Alter a materialized view (MV)
        • Drop a materialized view
        • Frequently asked questions about materialized views
      • Indexing Tables
        • Indexing concepts
        • Storage-Attached Indexing (SAI) Overview
          • SAI concepts
          • SAI Quickstart
          • SAI FAQ
          • Create SAI index
          • Alter SAI index
          • Drop SAI index
          • Querying with SAI
          • Configure SAI indexes
          • Monitor SAI indexes
          • SAI write path and read path
        • Secondary indexes (2i) overview
          • Secondary index (2i) concepts
          • When to use an index
          • Building and maintaining secondary indexes (2i)
          • Create a secondary index (2i)
            • Create a 2i on a collection column
          • Check secondary index (2i) existence
          • Alter a secondary index (2i)
          • Drop a secondary index (2i)
        • Search indexes overview
          • Search index commands
          • Adjusting timeout for index management
          • Creating a search index
          • Configuring search index joins
          • Joining cores
          • Reloading the search index
          • Removing a search index
          • Managing search index fields
            • Syntax for changing schema settings
            • Search index schema field types
            • Adding a new field type
            • Adding a column to the index
            • Indexing tuples and UDTs fields
              • Tuple configuration example
              • UDT configuration example
              • Nesting tuples and UDTs
              • Tuples and UDTs as CQL map values
            • Indexing map columns
            • Indexing a column for different analysis
            • Dropping columns from the index
          • Updating the index after data expires (TTL)
          • Inserting, updating, and deleting data
          • Search indexing examples
        • Search index examples
          • Search index examples
            • Creating a demo keyspace for tutorials
            • Indexing and querying polygons
      • Inserting and updating data
        • Insert simple data
        • Set column
        • List fields
        • Map fields
        • Tuple
        • User-defined type (UDT) column
        • Insert static data
        • UUID and timeuuid column
        • Date column
        • Time column
        • Timestamp column
        • Duration column
        • Update counter
        • Lightweight transactions (LWTs)
        • Inserting JSON formatted values
        • Batching inserts and updates
          • Batching inserts, updates, and deletes
          • Good use of BATCH statement
          • Misuse of BATCH statement
        • Importing data from a CSV file
        • Setting the time-to-live (TTL) for value
          • Inserting, updating, and deleting data
      • Deleting data
        • Deleting values from a column or entire row
        • Expiring data with time-to-live
        • Expiring data with TTL example
      • Querying and retrieving data
        • Using a SELECT statement
        • Restricting queries using WHERE clauses
          • Partition keys
          • Clustering columns
          • Retrieval using the IN keyword
          • Sorting and limiting results
        • Returning data from collection columns
        • Aggregating results
        • Using user-defined functions (UDF)
        • Applying user-defined aggregate (UDA) functions
          • Testing performance impact using tracing
        • Formatting query results as JSON
        • Retrieving the write timestamp
        • Using tracing
          • Tracing performance
        • DSE Search index querying
        • Search index filtering best practices
          • Search index syntax
          • search-index:si-query-syntax.adoc#siIndexedColumns
          • search-index:si-query-syntax.adoc#basicSolrSyntax
          • search-index:si-query-syntax.adoc#queriesJSON
          • search-index:si-query-syntax.adoc#siEscapeCharacters
        • Native CQL search queries
        • Identifying the partition key
        • Filtering on terms
          • Filtering on words, phrases, or substrings
          • Fuzzy search
        • UDT query examples
        • Querying a CQL collection set
        • Using date ranges in solr_query
        • Geospatial queries for Point and LineString
        • Spatial queries with polygons require JTS
        • Using dynamic fields
        • Limiting results and paging
        • Restricted query routing
    • Securing overview
      • Security quickstart
      • Using cqlsh with authentication
      • System tables for authentication and authorization
  • Cycling Examples
    • Setting up the cycling keyspace
    • User-defined types (UDTs)
      • basic_info
      • basic_info_withTTL
      • fullname
      • race
    • User-defined functions (UDFs) and user-defined aggregates (UDAs)
      • flog
      • left
      • average_state
      • average_final
      • Cycling user-defined aggregate team_average
    • Tables
      • birthday_list
      • calendar
      • comments
      • country_flag
      • cyclist_alt_stats
      • cyclist_base
      • cyclist_career_teams
      • cyclist_category
      • cyclist_emails
      • cyclist_expenses
      • cyclist_id
      • cyclist_name
      • cyclist_points
      • cyclist_races
      • cyclist_sponsors
      • cyclist_stats
      • cyclist_teams
      • events
      • popular_count
      • race_sponsors
      • race_starts
      • race_times
      • race_winners
      • rank_by_year_and_name
      • team_average
      • upcoming_calendar
    • Materialized views (MVs)
      • cyclist_by_age-mv
    • Search indexes
      • Search index examples
      • comments search index
    • SASI indexes
      • Index on cyclist_name
    • Access control
      • Cycling internal
    • Cycling queries
      • Aggregating cycling data
    • Reference
      • CQL quick reference
      • Understanding the CQL command syntax
      • Data types
        • Creating a blob column
        • Date, time, and timestamp format
        • Solr field type reference for DSE Search
      • Operators
      • CQL native functions
      • CQL native aggregates
      • System and virtual tables
        • System tables
          • Keyspace tables
          • Querying system tables
          • Functions, aggregates, and user types
        • Virtual tables
          • Virtual keyspaces and tables
          • Virtual tables for SAI indexes and SSTables
      • cqlsh (startup options)
        • Configuring a cqlshrc file
        • Starting cqlsh on a search node
      • CQL shell (cqlsh) reference
        • CAPTURE
        • CLEAR
        • CONSISTENCY
        • COPY TO
        • COPY FROM
        • DESCRIBE AGGREGATE
        • DESCRIBE CLUSTER
        • DESCRIBE SCHEMA
        • DESCRIBE FUNCTION
        • DESCRIBE INDEX
        • DESCRIBE KEYSPACE
        • DESCRIBE MATERIALIZED VIEW
        • DESCRIBE SEARCH INDEX
        • DESCRIBE TABLE
        • DESCRIBE TYPE
        • EXECUTE AS
        • EXPAND
        • EXIT
        • LOGIN
        • PAGING
        • SERIAL CONSISTENCY
        • SHOW
        • SOURCE
        • TIMING
        • TRACING
      • CQL commands
        • ALTER KEYSPACE
        • ALTER MATERIALIZED VIEW
        • ALTER ROLE
        • ALTER SEARCH INDEX CONFIG
        • ALTER SEARCH INDEX SCHEMA
        • ALTER TABLE
        • ALTER TYPE
        • ALTER USER (Deprecated)
        • BATCH
        • COMMIT SEARCH INDEX
        • CREATE AGGREGATE
        • CREATE CUSTOM INDEX
        • CREATE FUNCTION
        • CREATE INDEX
        • CREATE KEYSPACE
        • CREATE MATERIALIZED VIEW
        • CREATE ROLE
        • CREATE SEARCH INDEX
        • CREATE TABLE
        • CREATE TYPE
        • CREATE USER (Deprecated)
        • DELETE
        • DROP AGGREGATE
        • DROP FUNCTION
        • DROP INDEX
        • DROP KEYSPACE
        • DROP MATERIALIZED VIEW
        • DROP ROLE
        • DROP SEARCH INDEX
        • DROP TABLE
        • DROP TYPE
        • DROP USER (Deprecated)
        • GRANT
        • INSERT
        • LIST PERMISSIONS
        • LIST ROLES
        • LIST USERS (Deprecated)
        • REBUILD SEARCH INDEX
        • RELOAD SEARCH INDEX
        • RESTRICT
        • RESTRICT ROWS
        • REVOKE
        • SELECT
        • TRUNCATE
        • UNRESTRICT
        • UNRESTRICT ROWS
        • UPDATE
        • USE
  • CQL for DSE
  • Developing
  • Indexing Tables
  • Secondary indexes (2i) overview
  • When to use an index
Edit this Page

When to use an index

Built-in indexes are best on a table having many rows that contain the indexed value. The more unique values that exist in a particular column, the more overhead on average is required to query and maintain the index. For example, suppose you had a races table with a billion entries for cyclists in hundreds of races and wanted to look up rank by the cyclist. Many cyclists' ranks will share the same column value for race year. The race_year column is a good candidate for an index.

If secondary indexes are required, based on one or more table columns other than its partition key, use Storage-Attached Indexing (SAI). For details, see CREATE CUSTOM INDEX.

When not to use an index

Do not use an index in these situations:

  • On high-cardinality columns for a query of a huge volume of records for a small number of results. See Problems using a high-cardinality column index below.

  • In tables that use a counter column.

  • On a frequently updated or deleted column. See Problems using an index on a frequently updated or deleted column below.

  • To look for a row in a large partition unless narrowly queried. See Problems using an index to look for a row in a large partition unless narrowly queried below.

  • Do not add a secondary index and a search index to the same table.

Problems using a high-cardinality column index

If you create an index on a high-cardinality column, which has many distinct values, a query between the fields incurs many seeks for very few results. In the table with a billion songs, looking up songs by writer (a value that is typically unique for each song) instead of by their recording artist is likely to be very inefficient.

It would probably be more efficient to manually maintain the table as a form of an index instead of using the built-in index. For columns containing unique data, it is sometimes better for performance to use an index for convenience, as long as the query volume to the table having an indexed column is moderate and not under constant load.

Conversely, creating an index on an extremely low-cardinality column, such as a boolean column, does not make sense. Each value in the index becomes a single row in the index, resulting in a huge row for all the false values, for example. Indexing a multitude of indexed columns having foo = true and foo = false is not useful.

Problems using an index on a frequently updated or deleted column

The database stores tombstones in the index until the tombstone limit reaches 100K cells. After exceeding the tombstone limit, the query that uses the indexed value will fail.

Problems using an index to look for a row in a large partition unless narrowly queried

A query on an indexed column in a large cluster typically requires collating responses from multiple data partitions. The query response slows down as more machines are added to the cluster. When looking for a row in a large partition, narrow the search to avoid query performance degradation.

Secondary index (2i) concepts Building and maintaining secondary indexes (2i)

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