[
https://issues.apache.org/jira/browse/BEAM-12730?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17435918#comment-17435918
]
Etienne Chauchot commented on BEAM-12730:
-----------------------------------------
Hi [~EugeneNikolaiev]. It's been years since I coded that, so I had to take a
look at the code. Yes bundle split can happen at any byte so it can cut a
multi-byte delimiter so we have to go backward in parsing to be sure we get the
whole delimiter and we have data completeness.
Regarding self overlap: such as {{||}} for example: how should we interpret
{{abc|||xyz}} - as {{abc|}}, {{xyz}} - or as {{abc}}, {{|xyz}}? And how do we
consistently enforce this interpretation if the file is split by the runner
into bundles differently each time?
At parsing I cannot rewind the offset of {{(separator.size + 1)}} to allow only
one byte overlap, neither can I rewind the offset of {{(2*sperator.size)}} to
allow maximum overlap because it might produce duplicate record if a
{{record.size < separator.size}}. I cannot either catch anything to state that
the file format is wrong in case of overlap because I will get no exception,
just flaky record content depending on the runner / source split point.
So we decided to disallow overlapping delimiters. I advice you should disallow
overlapping delimiters for python as well for the same reasons + consistency
with the java sdk
> Add custom delimiters to Python TextIO reads
> --------------------------------------------
>
> Key: BEAM-12730
> URL: https://issues.apache.org/jira/browse/BEAM-12730
> Project: Beam
> Issue Type: New Feature
> Components: io-py-common, io-py-files
> Reporter: Daniel Oliveira
> Assignee: Dmitrii Kuzin
> Priority: P2
> Labels: beginner, newbie, starter
> Time Spent: 18h 10m
> Remaining Estimate: 0h
>
> A common request by users is to be able to separate a text files read by
> TextIO with delimiters other than newline. The Java SDK already supports this
> feature.
> The current delimiter code is [located
> here|https://github.com/apache/beam/blob/v2.31.0/sdks/python/apache_beam/io/textio.py#L236]
> and defaults to newlines. This function could easily be modified to also
> handle custom delimiters. Changing this would also necessitate changing the
> API for the various TextIO.Read methods and adding documentation.
> This seems like a good starter bug for making more in-depth contributions to
> Beam Python.
--
This message was sent by Atlassian Jira
(v8.3.4#803005)
