Why You Should Consider Implementing Indexed Views Alex Fleming Why You Should Consider Implementing Indexed Views

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Should You Create Indexed Views?

No.

Thank you

What is an Indexed View?

Indexed (or “Materialized”) view – a schemabound view in which data is persisted on disc in the format of a unique clustered index What does that mean? 1) Querying the view does not require base table access 2) Updates, Inserts, and Deletes require additional overhead

Demo #1

Why should you create Indexed Views?

Primary benefits: increase the performance of queries that contain: Expensive aggregate calculations Expensive join logic Queries that join hierarchies Relatively fast implementation Ancillary benefits: referential integrity enforcement manage code complexity Performance tuning slow reports? Performance tuning an application?

Other benefits: Increase awareness of dependent objects during development (schemabinding requirement) Enforce uniqueness for known (i.e., not null) values while allowing nulls (without using triggers) They’re cool! Encourage some best-practices (more on this later)

Important Indexed View Considerations

Does the data change frequently in the base tables? Numerous limitations (especially T-SQL) Are report tables an option? Is TempDB heavily utilized already? SQL Server Edition (Enterprise or Developer?) Express Edition requires WITH (NOEXPAND) hint

Indexed View Pre-requisites

2) Deterministic functions only 3) SET options 1) SCHEMABINDING 2) Deterministic functions only 3) SET options 4) Unique Clustered Index Two-part naming required (i.e., [schema].[table]) COUNT_BIG(*) How DML is tracked on underlying tables

SCHEMABINDING Prevent changes on parent objects from breaking child objects “Safety” feature – best practices? Slight Performance enhancement eliminate the need for Halloween Protection “Eager Table Spool” Plan operator

Deterministic Functions Deterministic function – return the same output for any set of inputs Three types of functions: Deterministic functions Non-deterministic functions Functions that vary on determinism qualities depending on use

SET Options (Part 1) SET ANSI_NULLS ON; SET ANSI_PADDING ON; SET ANSI_WARNINGS ON; Divide by 0 and arithmetic overflow cause rollback + warning warning when NULL appears in aggregate functions Parameters are unaffected (UDFs, Stored Procs, variables in batch statements) SET ARITHABORT ON; Implicitly turned on when ANSI_WARNINGS is on Performance issues arise when turned off SET CONCAT_NULL_YIELDS_NULL ON; SET NUMERIC_ROUNDABORT OFF; SET QUOTED_IDENTIFIER ON;

SET Options (Part 2)

SET Options (Part 3)

Alternatives Reporting Tables - No T-SQL restrictions, SET options, SCHEMABINDING, etc. - Require ETL process to load & refresh the table - Other queries that don’t directly reference the table can’t benefit from the table’s index(es)

Demo #2

Indexed View Opportunity Recognition Analyze existing view definitions Are any schemabound already? If so, are any indexable? select OBJECTPROPERTY(OBJECT_ID(‘[schema name].[view name]'),'IsIndexable’); Can you modify the view definition and remove T-SQL not supported by indexed views, and re-add the logic to a query referencing the indexed view?

Bugs Availability Groups Indexed View bug Brent Ozar - May 2018 SQL Server 2017 Memory dumps for queries on replicas that reference a dropped index on the indexed view Azure SQL DB – secondary replicate restart on 1st query failure Solution: DBCC FREESYSTEMCACHE('ALL'); Scalar Aggregates Indexed View bug Paul White - April 2018 Insert/deletes on base table Only affects scalar (not vector) aggregates

Monitoring Scalar Aggregate Bug DBCC CHECKDB (‘IndexedViewName’); is not good enough for scalar aggregate bug detection Compatibility level 100+ Instead: Create a backup Run this on the backup: DBCC CHECKDB(‘IndexedViewName’) WITH EXTENDED_LOGICAL_CHECKS; (Thank you Kendra Little!)

Further Reading docs.microsoft.com https://docs.microsoft.com/en-us/sql/relational-databases/views/create-indexed-views?view=sql-server-2017 https://docs.microsoft.com/en-us/sql/relational-databases/user-defined-functions/deterministic -and-nondeterministic-functions?view=sql-server-2017 https://docs.microsoft.com/en-us/sql/t-sql/statements/set-ansi-nulls-transact-sql?view=sql-server-2017 https://docs.microsoft.com/en-us/sql/t-sql/statements/set-ansi-warnings-transact-sql?view=sql-server-2017 https://docs.microsoft.com/en-us/sql/t-sql/statements/set-arithabort-transact-sql?view=sql-server-2017 https://docs.microsoft.com/en-us/sql/t-sql/statements/set-concat-null-yields-null-transact-sql?view=sql-server-2017 https://docs.microsoft.com/en-us/sql/t-sql/statements/set-quoted-identifier-transact-sql?view=sql-server-2017 Darling, Erik. “Indexed Views and Data Modifications.” https://www.brentozar.com/archive/2017/03/indexed-views-data-modifications/ Ozar, Brent. “What You Can (And Can’t) Do With Indexed Views.” https://www.brentozar.com/archive/2013/11/what-you-can-and-cant-do-with-indexed-views/ Ozar, Brent. “Availability Groups Bug with Indexed Views.” https://www.brentozar.com/archive/2018/05/availability-groups-bug-with-indexed-views/ Hammer, Derik. “SQL Server Schemabinding.” https://www.sqlhammer.com/sql-server-schemabinding/ Little, Kendra. “Find Corrupted Indexed Views with DBCC CHECKDB.” https://www.brentozar.com/archive/2015/04/find-corruption-indexed-view-dbcc-checkdb/ Borland, Jes. “SQL Server Indexed Views: The Basics.” https://www.red-gate.com/simple-talk/sql/learn-sql-server/sql-server-indexed-views-the-basics/ Ben-Gan, Itzik. “Views.” Inside Microsoft SQL Server 2008. (1-29). Korotkevitch, Dmitri. “Indexed (Materialized) Views.” Pro SQL Server Internals. (219-225). White, Paul. “An Indexed View Bug with Scalar Aggregates.” https://sqlperformance.com/2015/04/sql-indexes/an-indexed-view-bug-with-scalar-aggregates StackOverflow Database download link and instructions (Thank you Brent!): https://www.brentozar.com/archive/2015/10/how-to-download-the-stack-overflow-database-via-bittorrent/ Shaw, Gail. “Gail Shaw’s SQL Server Howlers.” https://www.red-gate.com/simple-talk/sql/database-administration/gail-shaws-sql-server-howlers/