[Java] Why does VectorSchemaRoot::slice return reference to same root when slice index is [0, rowCount] ?

[ParthChonkar]

Describe the usage question you have. Please include as many useful details as possible.

Hi Arrow community,

In the VectorSchemaRoot::slice implementation it checks if the slice covers the entirety of the root and returns the reference to the same root if so.

    if (index == 0 && length == rowCount) {
      return this;
    }

Looks like this is done as an optimization to prevent creating another root + transferring to it.

Doesn't this optimization make slice inconsistent? Sometimes you get back a new autocloseable resource that has to be separately closed and sometimes you get back the same root.

So if you want to calculate something based on a set of different slices of your root then you have to manually check whether the current slice you are requesting isn't the whole root to avoid closing the original root.

Since splitAndTransfer do no copying of the actual data, is this optimization worth this tradeoff?

Component(s)

Java

[ParthChonkar]

Also in this documentation https://arrow.apache.org/docs/java/vector_schema_root.html#vectorschemaroot
it says that A **new** VectorSchemaRoot can be sliced from an existing root without copying data: