[jira] [Created] (HDDS-15184) Atomic Create-If-Absent Should Use 0 for Generation Match

["Chu Cheng Li (Jira)" <ji...@apache.org>]

Chu Cheng Li created HDDS-15184:
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             Summary: Atomic Create-If-Absent Should Use 0 for Generation Match
                 Key: HDDS-15184
                 URL: https://issues.apache.org/jira/browse/HDDS-15184
             Project: Apache Ozone
          Issue Type: Sub-task
          Components: OM, s3gateway
            Reporter: Chu Cheng Li
            Assignee: Chu Cheng Li


We currently use an expected data generation of -1 to represent “create if absent”. In contrast, GCS uses {{--if-generation-match=0}} for its create-if-absent semantics.

One potential concern is whether the first object we create in Ozone could have a generation/update ID of 0, which would conflict with this encoding. In practice, this does not happen: committed keys in Ozone derive their {{updateID}} from the Ratis transaction index at commit time ({{{}OMKeyCommitRequest.java{}}}, around line 344). The very first Ratis index (0) is reserved for startup/configuration log state before any client writes, so actual OM write requests always receive positive indices. As a result, committed keys will never have {{{}updateID == 0{}}}, and using 0 to encode “absent” is safe.



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