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https://issues.apache.org/jira/browse/HIVE-16704?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Teddy Choi reassigned HIVE-16704:
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> Replace vector code generation with stream and lambdas
> ------------------------------------------------------
>
> Key: HIVE-16704
> URL: https://issues.apache.org/jira/browse/HIVE-16704
> Project: Hive
> Issue Type: Improvement
> Reporter: Teddy Choi
> Assignee: Teddy Choi
>
> Hive uses vectorized execution engine. It uses code generator to cover
> various data types. Because Java compiler recognizes and optimizes only
> simple code loop with primitive data types and operators, not conditional
> branches, such as IF or SWITCH. The code generator and its generated code is
> hard to read and maintain.
> Meanwhile, Hive 3 used Java 8+, which introduced lambda and new Stream API.
> Lambda with new Stream API is an excellent replacement for vector code
> generation. It is more concise, because it doesn't make several copies of the
> template code for each class. It's more precise, because the template code
> and string replacement allowed only some data types and operators, not whole
> code blocks with compiler support. It's still fast, because Java 8 compiler
> optimizes primitive data type operations in lambda as a loop. Therefore, it
> will give more space to memory and more readability and extensibility to
> programmers.
> The vector code generation part is huge. So it needs to be divided in small
> sub-tasks. I will start with ColumnArithmeticColumn for long, which covers
> LongColAddLongColumn, LongColSubtractLongColumn, and
> LongColMultiplyLongColumn.
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