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https://issues.apache.org/jira/browse/HBASE-11135?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13994798#comment-13994798
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Jeffrey Zhong commented on HBASE-11135:
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Sorry [[email protected]]. I mean the following you mentioned earlier:
{quote}
Let me play w/ doing original idea of two ring buffers – a fast, front one and
then a slow back one to do appends and syncs.
{quote}.
{quote}
If we do double ring buffer, we will still have to do thread handoff across the
first buffer so I foresee us having the same slow down only w/ a more complex
system. What you think?
{quote}
Ok. Fair enough then don't do it.
{quote}
Does this patch get you what you wanted and unblocks your mvcc + sequence id
unificattion?
{quote}
I think so. How long could you hold before check it in? To be conservative, I
can firstly migrate my patch on top of your patch and run all tests. How do you
think? Thanks.
> Change region sequenceid generation so happens earlier in the append cycle
> rather than just before added to file
> ----------------------------------------------------------------------------------------------------------------
>
> Key: HBASE-11135
> URL: https://issues.apache.org/jira/browse/HBASE-11135
> Project: HBase
> Issue Type: Sub-task
> Components: wal
> Reporter: stack
> Assignee: stack
> Attachments: 11135.wip.txt, 11135v2.txt, 11135v5.txt, 11135v5.txt
>
>
> Currently we assign the region edit/sequence id just before we put it in the
> WAL. We do it in the single thread that feeds from the ring buffer. Doing
> it at this point, we can ensure order, that the edits will be in the file in
> accordance w/ the ordering of the region sequence id.
> But the point at which region sequence id is assigned an edit is deep down in
> the WAL system and there is a lag between our putting an edit into the WAL
> system and the edit actually getting its edit/sequence id.
> This lag -- "late-binding" -- complicates the unification of mvcc and region
> sequence id, especially around async WAL writes (and, related, for no-WAL
> writes) -- the parent for this issue (For async, how you get the edit id in
> our system when the threads have all gone home -- unless you make them wait?)
> Chatting w/ Jeffrey Zhong yesterday, we came up with a crazypants means of
> getting the region sequence id near-immediately. We'll run two ringbuffers.
> The first will mesh all handler threads and the consumer will generate ids
> (we will have order on other side of this first ring buffer), and then if
> async or no sync, we will just let the threads return ... updating mvcc just
> before we let them go. All other calls will go up on to the second ring
> buffer to be serviced as now (batching, distribution out among the sync'ing
> threads). The first rb will have no friction and should turn at fast rates
> compared to the second. There should not be noticeable slowdown nor do I
> foresee this refactor intefering w/ our multi-WAL plans.
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