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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