tarak271 opened a new pull request, #6800:
URL: https://github.com/apache/hive/pull/6800
…er lines for skip.header/footer.line.count, causing data loss on append
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### What changes were proposed in this pull request?
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Hive’s default text file writer (**HiveIgnoreKeyTextOutputFormat**) was
updated so that when a table is defined with skip header and/or skip footer
table properties, the files Hive creates during **INSERT** and **INSERT
OVERWRITE** include the matching placeholder lines:
**Header**: Before data rows, the writer adds header line(s). The first line
is built from the table’s column names, using the same field delimiter (and
quoting rules when needed) as the table. If skip.header.line.count is greater
than 1, additional header lines are written as empty lines.
**Footer**: Before the file is closed, the writer adds empty footer lines
according to skip.footer.line.count.
### Why are the changes needed?
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These table properties tell Hive’s reader to skip the first N lines (header)
and last M lines (footer) in each text file. That works when files come from
outside systems (for example CSV exports with a real header row).
When Hive writes those tables itself, the writer used to output only data
rows—no header or footer lines. On read, Hive still skipped N/M lines from
every file, so the first and/or last data rows were treated as header/footer
and **dropped**. That showed up as missing rows after INSERT, especially on the
first row when skip.header.line.count=1.
### Does this PR introduce _any_ user-facing change?
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No
### How was this patch tested?
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New unit tests (TestHiveIgnoreKeyTextOutputFormat):
Existing unit tests for skip-on-read (TestSkippingTextInputFormat)
skip_header_footer_proj.q and related LLAP q-tests
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