Teddy Choi created HIVE-16704:
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Summary: 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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