[GitHub] [arrow] westonpace commented on pull request #10202: ARROW-12673: [C++] Add parser handler for incorrect column counts

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westonpace commented on pull request #10202:
URL: https://github.com/apache/arrow/pull/10202#issuecomment-872540450


   I'm not sure there is an obvious way to solve this problem in parallel.  The parser will start parsing block X before block X-1 has finished parsing.  The parser input (CSVBlock) doesn't know how many lines it has.  That is not discovered until parsing time.  So, for example, the parser for block 2 might realize there is an error on the third line of block 2.  But, without knowing how many lines are in block 1 (and block 1 may not have finished parsing) it is hard to say what the lines number of that error is.
   
   You could do a serial pass prior to parsing that just figures out how many lines are in a block but I suspect that would be too much overhead.
   
   You could delay reporting an error on block X until blocks 1 to (X-1) have finished parsing (so you can know what the line number is).  That would probably be the solution I would take if I needed to do this.  However, I don't know off-hand how to do that delay in a low-complexity way.


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