Dear all, A non-nullable vector is one that is guaranteed to contain no nulls. We want to support non-nullable vectors in Java.
*Motivations:* 1. It is widely used in practice. For example, in a database engine, a column can be declared as not null, so it cannot contain null values. 2.Non-nullable vectors has significant performance advantages compared with their nullable conterparts, such as: 1) the memory space of the validity buffer can be saved. 2) manipulation of the validity buffer can be bypassed 3) some if-else branches can be replaced by sequential instructions (by the JIT compiler), leading to high throughput for the CPU pipeline. *Potential Cost:* For nullable vectors, there can be extra checks against the nullablility flag. So we must change the code in a way that minimizes the cost. *Proposed Changes:* 1. There is no need to create new vector classes. We add a final boolean to the vector base classes as the nullability flag. The value of the flag can be obtained from the field when creating the vector. 2. Add a method "boolean isNullable()" to the root interface ValueVector. 3. If a vector is non-nullable, its validity buffer should be an empty buffer (not null, so much of the existing logic can be left unchanged). 4. For operations involving validity buffers (e.g. isNull, get, set), we use the nullability flag to bypass manipulations to the validity buffer. Therefore, it should be possible to support the feature with small code changes. BTW, please note that similar behaviors have already been supported in C++. Would you please give your valueable feedback? Best, Liya Fan
