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https://issues.apache.org/jira/browse/HBASE-25913?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Andrew Kyle Purtell updated HBASE-25913:
----------------------------------------
Description:
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.
was:
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, release the locks. I don't think this
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.
> 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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