refactor: rename Update operation fields

[yanghua]

When I work on #4589, I found the field fields_modified in Update operation is hard to understand, there are four places we need to set it when updating:

• pure update;
• merge insert(two full schema) and sub col;

In some places, it is not based on the naming to set the modified fields. For example, here and here.

Actually, it is used to prune the index's frag bitmap based on some fields.

IMO, we could rename them(another one is fields_for_preserving_frag_bitmap) for a better name based on their purpose.

[codecov-commenter]

Codecov Report

❌ Patch coverage is 94.28571% with 4 lines in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
rust/lance/src/dataset/transaction.rs	84.00%	4 Missing ⚠️

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[jackye1995]

I think a problem is that the train has already been released, it is hard to now change the name. What about we just add more documentation in the transaction protobuf definition and rust struct so people can better understand what those fields mean? I am working on fully refreshing the table spec, so once we update the proto the expectation is that it will be displayed in the spec doc in the future automatically.

[yanghua]

I think a problem is that the train has already been released, it is hard to now change the name.

What does the train mean? Do you mean the compatibility?

It seems protobuf is really an issue that would cause compatibility. Not sure if the community would introduce a fallback configuration mapping mechanism in the future. What about doing this:

• for fields in pb and rust struct, use the old names;
• for general variable naming them to be the new;

WDYT?

[jackye1995]

What does the train mean? Do you mean the compatibility?

yeah sorry I mean a release train

for fields in pb and rust struct, use the old names;
for general variable naming them to be the new;

I could see the point for fields_modified, but how is bitmap_preserve_field_ids better than fields_for_preserving_frag_bitmap? Aren't we just changing the position of the words?

[yanghua]

but how is bitmap_preserve_field_ids better than fields_for_preserving_frag_bitmap? Aren't we just changing the position of the words?

My original thought is that if fields_modified could be changed to be bitmap_prune_field_ids, as a similar purpose field, fields_for_preserving_frag_bitmap could be aligned to bitmap_preserve_field_ids. It also makes the naming more concise. But the main motivation is to align with bitmap_prune_field_ids.

[yanghua]

@jackye1995 I did a trade-off: keep the old name in pb to keep compatibility, just renamed the other fields to make them follow the real semantics and better readability. WDYT?