Do we still need `DataReplacement` operation?

[westonpace]

In #4715 we are replacing one or more columns using an Update operation. What is the difference between DataReplacement and Update?

[westonpace]

CC @jackye1995 @wjones127

[wjones127]

Perhaps not. I can't think of why we need both at the moment.

[majin1102]

I have a similar question.

When I was adapting merge operation for Java module. I found that merge could almost replace all fragment level operations.

I added a vaildate logic for it #4532. But I think the operation still too flexible to use. I could use merge to do the same thing in #4715 instead of Update

Maybe we could clarify the operations and establish certain guidelines and constraints?

[steFaiz]

I have a similar question.

When I was adapting merge operation for Java module. I found that merge could almost replace all fragment level operations.

I added a vaildate logic for it #4532. But I think the operation still too flexible to use. I could use merge to do the same thing in #4715 instead of Update

Maybe we could clarify the operations and establish certain guidelines and constraints?

@majin1102 I agree with you, I think the Merge transaction is a little bit tricky to use e.g. the fragments list in the Merge Operation will override current fragments, which I think is not aligned with the 'Merge' semantic. (But Update Operation will retrieve current fragments and merge the new fragments into the final list)

[westonpace]

From a mechanics standpoint, merge is a superset of update. There is a subtle difference between the two. Update will not remove fragments introduced between <read_version> and <commit_version>. Merge will remove fragments introduced between <read_version> and <commit_version>. Merge always replaces all fragments in the dataset which is very blunt.

As a result, Merge is much more brittle when it comes to conflict resolution. Merge will conflict with Append while Update never does. Also, Merge will always conflict with Delete and Rewrite but Update will only conflict if there is fragment overlap.