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https://issues.apache.org/jira/browse/ARROW-18161?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17624887#comment-17624887
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Kouhei Sutou commented on ARROW-18161:
--------------------------------------
Thanks.
{{Arrow::Table.new(**table)}} is the cause of this problem.
We need to keep {{Arrow::Buffer}} for each {{arrow_frame[key].value}} while
{{Arrow::Table.new(\*\*table)}} object is alive to avoid memory copy.
{{Arrow::Table.load(Arrow::Buffer.new)}} keeps a reference to the given
{{Arrow::Buffer}} but {{Arrow::table.new(\*\*table)}} doesn't. So
{{Arrow::Buffer}} s are GC-ed.
How about the following for now?
{code:ruby}
def _get_arrow_frame_from_proto_arrow_frame(arrow_frame)
columns = {}
buffers = []
arrow_frame.keys.each do |key|
buffer = Arrow::Buffer.new(arrow_frame[key].value)
buffers << buffer
tmp = Arrow::Table.load(buffer)
col_name = create_friendly_name_for_key(key)
columns[col_name] = tmp[0].data
end
table = Arrow::Table.new(**columns)
table.instance_variable_set(:@buffers, buffers)
table
end
{code}
We can avoid the {{instance_variable_set}} in the future by referring the
associated buffer from all related objects such as {{Arrow::ChunkedArray}} in
{{Arrow::Table}}.
> Reading error table causes mutations
> ------------------------------------
>
> Key: ARROW-18161
> URL: https://issues.apache.org/jira/browse/ARROW-18161
> Project: Apache Arrow
> Issue Type: Bug
> Components: Ruby
> Affects Versions: 9.0.0
> Environment: Ruby 3.1.2
> Reporter: Noah Horton
> Assignee: Kouhei Sutou
> Priority: Major
>
> ven an Arrow::Table with several columns "X"
>
> {code:ruby}
> # Rails console outputs
> 3.1.2 :107 > x.schema
> =>
> #<Arrow::Schema:0x7ff2fbc426d8 ptr=0x55851587bc20 actual_values: int64
> dates: date32[day]
> expected_values: double>
> 3.1.2 :108 > x.schema
> =>
> #<Arrow::Schema:0x7ff2fbbcda68 ptr=0x55851a541020 actual_values: int64
> dates: date32[day]
> expected_values: double>
> 3.1.2 :109 > {code}
> Note that the object and pointer have both changed values.
> But the far bigger issue is that repeated reads from it will cause different
> results:
> {code:ruby}
> 3.1.2 :097 > x[1][0]
> => Sun, 22 Aug 2021
> 3.1.2 :098 > x[1][1]
> => nil
> 3.1.2 :099 > x[1][0]
> => nil {code}
> I have a lot of issues like this - when I have done these types of read
> operations, I get the original table with the data in the columns all
> shuffled around or deleted.
> I do ingest the data slightly oddly in the first place as it comes in over
> GRPC and I am using Arrow::Buffer to read it from the GRPC and then passing
> that into Arrow::Table.load. But I would not expect that once it was in
> Arrow::Table that I could do anything to permute it unintentionally.
>
>
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