just-in-time indexes

Just-in-Time Indexes

Understanding Indexes in KB_SQL

March 2001

March 2001

Learning Objectives

• What options do I have to improve query performance?

The answer is…indexes.

• Review indexing strategies

• Introduce just-in-time indexes

• Discuss advantages and caveats

Improve Performance

Why does my query run so slow?

Query Results

Show Plan/Stats: Query

Run query with Show Plan and Show Stats

Show Plan: Results

Note: No index being used

Show Stats: Results

Note: Selecting 9 of 25000 rows searched

Show All Plans: Query

Run query with SHOW_ALL_PLANS to see if index is available

Show All Plans: Results

Note: No indexes available

Index Exists

Define Index to KB_SQL

Add BY_NAME index in KB_SQL

New Show Plan

Note: BY_NAME index is used, cost is reduced

New Show Stats

Note: Selecting 9 of 9 rows searched

New Show All Plans

Note: BY_NAME index available

How do we improve performance if we don’t have sufficient indexes?

• What are the options?– Create supplemental table(s)– Build index– Create just-in-time index

• When will it be populated?

• How often should it be updated?

• Advantages and caveats?

Create Supplemental Tables

• Create new table

• Join to “base” table

Build the Index

• Benefits– Queries only look at key data which results

in faster searches

• Caveats– Time– Resources– Additional globals to maintain

What if there is no index?

What if there is no index? (cont)

What if there is no index? (cont)

Just-in-Time Indexes

• When will the index be populated?

• How often should the index be updated?

Just-in-Time Indexes: Advantages and Caveats

• Advantages over traditional indexes– Add only the indexes that the user

demands– Reduce wasted effort to build indexes that

won’t be used• Caveats

– Does not provide up-to-the-minute data accuracy

– 2 or more queries to realize benefit

Build the Just-in-Time Index

Define the Index to KB_SQL

New Show All Plans

Note: Two indexes available; BY_SUPPLIER is accepted based on constraint

New Show Plan

Note: BY_SUPPLIER index is used

New Show Stats

Note: Selecting 4 of 4 rows searched

Summary

• Discussed options available to help improve query performance

The answer is…indexes.

• Reviewed indexing strategies

• Introduced just-in-time indexes

• Discussed advantages and caveats