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From "Holger Stratmann (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (CSV-131) Save positions of records to enable random access
Date Mon, 10 Nov 2014 01:05:34 GMT

    [ https://issues.apache.org/jira/browse/CSV-131?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14204216#comment-14204216
] 

Holger Stratmann commented on CSV-131:
--------------------------------------

sorry again for being slow... got latest updates today to prepare a new patch, but saw that
you already made the changes I wanted to make. Current code is fine for me (I'll take another
look because something has changed in the numbering of records (when there's a header?) and
I still haven't had time to investigate this today) and I think it's the best solution (might
be even nicer to store a "recordOffset" instead of setting the recordNumber directly, but
it's fine like it is, I think we might be overengineering a simple field :)). Thanks for taking
care of this!

> Save positions of records to enable random access
> -------------------------------------------------
>
>                 Key: CSV-131
>                 URL: https://issues.apache.org/jira/browse/CSV-131
>             Project: Commons CSV
>          Issue Type: Improvement
>          Components: Parser
>    Affects Versions: 1.1
>            Reporter: Holger Stratmann
>            Priority: Minor
>         Attachments: CSV-131-gg-0.diff, PositionTrackingFull_v101_20140910.patch, PositionTrackingTest_20140907.patch,
PositionTracking_20140907.patch, ggregory-CSV-131-parser-and-record.diff
>
>   Original Estimate: 1h
>  Remaining Estimate: 1h
>
> It would be good to have {{CSVRecord}} save its position in the source stream.
> Reason: Knowing the position of the records would enable random access to retrieve records
from the source (after reading it once to build an index) if the file is too large to be read
into memory (or if we don't want to read the full file to access a record in the middle).
> Additional info: I have created a "random access csv reader" and a "csv viewer" (Swing)
for arbitrarily large CSV files. It requires one additional scan of the file to build an index
(multi-byte charsets supported). The index can be saved to a file so it only needs to be built
once. Because the lexer uses a BufferedReader, we need "internal information" to know where
each record starts.
> The change to "core" is minor: one field in {{CSVRecord}}s and some associated methods
to store the position.
> Patch will be attached.
> Code for random access (both UI and non-UI) will be proposed (and possibly submitted)
as a separate issue. It could also be an independent add-on but requires this one little change
to Commons CSV.



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