[jira] [Updated] (HBASE-25913) Introduce EnvironmentEdge.currentTimeAdvancing

["Andrew Kyle Purtell (Jira)" <ji...@apache.org>]

     [ https://issues.apache.org/jira/browse/HBASE-25913?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]

Andrew Kyle Purtell updated HBASE-25913:
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    Attachment: HBASE-25913_Multithreaded_Benchmarks.pdf

> Introduce EnvironmentEdge.currentTimeAdvancing
> ----------------------------------------------
>
>                 Key: HBASE-25913
>                 URL: https://issues.apache.org/jira/browse/HBASE-25913
>             Project: HBase
>          Issue Type: Sub-task
>            Reporter: Andrew Kyle Purtell
>            Assignee: Andrew Kyle Purtell
>            Priority: Major
>             Fix For: 3.0.0-alpha-1, 2.5.0
>
>         Attachments: 0001-HBASE-25913-Introduce-EnvironmentEdge-Clock-and-Cloc.patch, HBASE-25913_Multithreaded_Benchmarks.pdf, JMH-HBASE-25913.pdf, jmh-HBASE-25913.tar.gz
>
>
> Introduce new {{EnvironmentEdge#currentTimeAdvancing}} which ensures that when the current time is returned, it is the current time in a different clock tick from the last time the {{EnvironmentEdge}} was used to get the current time.
> When processing mutations we substitute the {{Long.MAX_VALUE}} timestamp placeholder with a real placeholder just before committing the mutation. The current code gets the current time for timestamp substitution while under row lock and mvcc. We will simply use {{EnvironmentEdge#currentTimeAdvancing}} instead of {{EnvironmentEdge#currentTime}} at this point in the code to ensure we have seen the clock tick over. When processing a batch of mutations (doMiniBatchMutation etc) we will call {{currentTimeAdvancing}} only once. This means the client cannot bundle cells with wildcard timestamps into a batch where those cells must be committed with different timestamps. Clients must simply not submit mutations that must be committed with guaranteed distinct timestamps in the same batch. Easy to understand, easy to document, and it aligns with our design philosophy of the client knows best.
> It is not required to handle batches as proposed. We could guarantee a distinct timestamp for every mutation in a batch. Count the number of mutations, call this M. Acquire all row locks and get the current time. Then, wait for at least M milliseconds. Then, set the first mutation timestamp with this value and increment by 1 for all remaining. Then, do the rest of mutation processing as normal. I don't think this extra waiting to reserve the range of timestamps is necessary. See reasoning in above paragraph. Mentioned here for sake of discussion.
> It will be fine to continue to use {{EnvironmentEdge#currentTime}} everywhere else. In this way we will only potentially spin wait where it matters, and won't suffer serious overheads during batch processing.



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