Purpose of IM expression (IM 5.2)

Upper connection IM 5.1, This chapter is IM Chapter 5 of the series Use In-Memory Expression optimization query part 2 IM The purpose of the expression .

IM The purpose of the expression

IM Expressions accelerate the query speed of large data sets by pre calculating dense expressions . IM Expressions are especially useful for frequently executed table joins , Mapping and predicate evaluation .

IM The main advantages of expressions are as follows ：

· The query does not need to recalculate the expression every time . If IM The column store does not populate the expression results , Then the database must calculate them for each row , This may be resource intensive . The database encountered errors during population CPU expenses .

· IM The implementation of expressions enables the database to take advantage of performance enhancements , Such as SIMD Vector processing and IMCU trim .

· It's the database , Not users , Track which expressions are the most active .

IM Expressions and materialized views solve the same problem ： How to avoid double evaluating expressions . However ,IM Expressions have advantages over materialized views ：

· IM Expressions can capture data that is not persisted .

for example ,IM Column storage can automatically cache internal calculations based on expressions in queries .

· Use... Effectively , The instantiated view must list all columns in the query , Otherwise, the query must be added to the view and base table . contrary , contain IM Any query of an expression can benefit .

· Automatic database identification and creation IM expression , And materialized view （ User created objects ） Different .

To be continued .

Here are IM Series content ：

In-Memory The manual : Preface （IM- Preface ）

Chapter one Oracle Database In-Memory Relevant concepts (IM-1.1)

Chapter one Oracle Database In-Memory Relevant concepts （ To continue ）(IM-1.2)

Chapter two Oracle Database In-Memory Architecture ( On ) (IM-2.1)

Chapter two In-Memory Architecture (IM-2.2)

Chapter two IM Architecture ：CPU framework ：SIMD Vector processing （IM-2.3）

The third chapter Enable and adjust IM The size of the column store （IM-3.1）

Chapter four by In-Memory Enable fill objects （IM-4.1 The first part ）

Chapter four by In-Memory Enable fill objects （IM-4.2 The second part ）

Chapter four by IM Enable and disable columns for fill objects （IM-4.3 The third part ）

Chapter four by IM Enables the placement of fill objects NO INMEMORY The table specifies INMEMORY Column properties ： Example （IM-4.4 The fourth part ）

Chapter four by IM Enable and disable tablespaces for padding objects IM Column store （IM 4.5）

Chapter four Enable and disable... For materialized views IM Column store （IM 4.6）

Chapter four by IM Enables forced filling of filled objects In-Memory object ： course （IM 4.7）

Chapter four by IM Enable fill objects to IM Column storage enabled ADO（IM 4.8） The fifth chapter Use In-Memory Expression optimization query （IM 5.1）

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