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Posted to issues@orc.apache.org by "lszskye (via GitHub)" <gi...@apache.org> on 2026/04/22 03:49:27 UTC

[PR] ORC-2151: Move the timestamp compensation before timezone conversion to prevent incorrect DST offset lookup [orc]

lszskye opened a new pull request, #2609:
URL: https://github.com/apache/orc/pull/2609

### What changes were proposed in this pull request?
Moving the compensation to before the timezone conversion, we ensure that getVariant() always receives the corrected wall-clock time, producing the correct DST offset and an accurate final result.

### Why are the changes needed?
Previously, the -1 second compensation for pre-1970 timestamps (caused by Java's truncating integer division in Timestamp.getTime()) was applied after the writer-to-reader timezone adjustment. This means writerTimezone.getVariant(writerTime) was called with an uncorrected writerTime that could be 1 second larger than the true value. If this 1-second discrepancy happens to cross a DST (Daylight Saving Time) boundary, the timezone lookup would return an incorrect GMT offset, causing the final timestamp result to be off by the entire DST shift (typically 1 hour) rather than just 1 second.

### Was this patch authored or co-authored using generative AI tooling?
No

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Re: [PR] ORC-2151: [C++] Move the timestamp compensation before timezone conversion to prevent incorrect DST offset lookup [orc]

Posted by "wgtmac (via GitHub)" <gi...@apache.org>.

wgtmac commented on code in PR #2609:
URL: https://github.com/apache/orc/pull/2609#discussion_r3162559403


##########
c++/test/TestWriter.cc:
##########
@@ -839,6 +839,73 @@ namespace orc {
     testWriteTimestampWithTimezone(fileVersion, "America/Los_Angeles", "America/Los_Angeles",
                                    "2014-06-06 12:34:56", IS_DST);
   }
+
+  // Test that the ORC-306 compensation (-1s for pre-1970 timestamps with
+  // nanos > 999999) is applied BEFORE timezone conversion in the Reader.
+  //
+  // We write secs = -5756401 (1s before the 1969 PDT->PST boundary in LA)
+  // with nanos = 1000000. The C++ Writer applies +1, storing -5756400 in the
+  // ORC file (exactly at the DST boundary). On read, the Reader must apply
+  // -1 BEFORE timezone conversion so that getVariant() sees -5756401 (PDT).
+  // If compensation were applied AFTER timezone conversion, getVariant() would
+  // see -5756400 (PST), producing a gmtOffset that differs by 3600 seconds.
+  TEST_P(WriterTest, DISABLED_writeNegativeTimestampAtDSTBoundary) {

Review Comment:
   As discussed offline, I've merged it to move forward. Thanks @lszskye for fixing this!



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