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https://issues.apache.org/jira/browse/HDDS-15184?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Chu Cheng Li updated HDDS-15184:
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Fix Version/s: 2.2.0
Resolution: Fixed
Status: Resolved (was: Patch Available)
> 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
> Priority: Major
> Labels: pull-request-available
> Fix For: 2.2.0
>
>
> 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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