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https://issues.apache.org/jira/browse/HBASE-25913?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17351194#comment-17351194
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Geoffrey Jacoby commented on HBASE-25913:
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[~apurtell] - Interesting. If I'm understanding properly, that's actually a
stronger guarantee than what Phoenix currently provides (or requires) when
doing global indexes.
(Phoenix, IIRC, guarantees that each mutation of a given row key will get a
distinct timestamp, but two batch mutations done in parallel on disjoint sets
of row keys might get the same mutation ts.) This proposal sounds like it gives
each mutation on a given RS a distinct timestamp, leading to a total ordering
of all mutations on a RS at the cost of limiting RS throughput to 1 batch
mutation / ms.
Since HBase doesn't provide any RS-level atomicity guarantees that I'm aware
of, should this be done at the Region level rather than RS to allow more
throughput? (Which would still be more than Phoenix needs, but probably useful
for other use cases.)
> 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
>
>
> 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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