my-ship-it commented on issue #1670:
URL: https://github.com/apache/cloudberry/issues/1670#issuecomment-4219410592

   Hi @adnanhamdussalam, thanks for the follow-up and for providing the 
additional details!
   
   After investigating this further, we've identified the **root cause**: 
Cloudberry is currently based on **PostgreSQL 14.4 (circa 2022)**, which ships 
with **tzdata version 2022a** (released March 2022). However, **Mexico 
officially abolished Daylight Saving Time in October 2022**, and this change 
was not included until **tzdata 2022f** (released October 2022). Since 
Cloudberry hasn't yet upgraded the bundled timezone data from the upstream 
PostgreSQL, the database still carries the outdated DST rules.
   
   Because of this, the database still applies the old DST rules for 
`America/Mexico_City`, switching to CDT (UTC-5) every April — which is no 
longer correct in the real world. Your OS has the updated timezone data and 
correctly shows CST (UTC-6), so the 1-hour discrepancy you're seeing is 
expected given this mismatch.
   
   **What the upstream fix looks like:**
   
   PostgreSQL addressed this by updating the bundled tzdata. Specifically, the 
Mexico DST rule was changed from:
   
   ```
   R m 2002 max - Apr Su>=1 2 1 D   (DST forever)
   ```
   to:
   ```
   R m 2002 2022 - Apr Su>=1 2 1 D  (DST ends in 2022)
   ```
   
   This means after 2022, `America/Mexico_City` will correctly stay on CST 
(UTC-6) year-round — which is exactly what you need. The relevant upstream 
commits are available from tzdata 2022f through 2025b.
   
   **Next steps:**
   
   We have verified that these tzdata updates (2022f → 2025b) can be cleanly 
cherry-picked and will backport the fix to the `REL_2_STABLE` branch. The **2.1 
release is currently being prepared**, and this fix will be included. We'll 
keep you posted on the progress.
   
   Thanks again for reporting this — it's a great catch and will benefit other 
users in regions affected by recent DST law changes!


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