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From "Jan Fernando (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (PHOENIX-1954) Reserve chunks of numbers for a sequence
Date Fri, 10 Jul 2015 03:09:04 GMT

    [ https://issues.apache.org/jira/browse/PHOENIX-1954?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14621645#comment-14621645
] 

Jan Fernando commented on PHOENIX-1954:
---------------------------------------

[~jamestaylor] 

#1 Let me look at removing the RESERVE_SEQUENCE enum now and see if there's any reason to
keep. I agree probably good to get rid of it, since we don't want allocations happening on
expression evaluation.

#2 The patch file I uploaded had 3 commits in it, you probably looked at yesterday's. Latest
version seems correct. I thought the multiple commit might make things clearer, but I was
wrong obviously :) After I look at #1 I'll rebase and generate a new patch which should be
clearer.

> Reserve chunks of numbers for a sequence
> ----------------------------------------
>
>                 Key: PHOENIX-1954
>                 URL: https://issues.apache.org/jira/browse/PHOENIX-1954
>             Project: Phoenix
>          Issue Type: New Feature
>            Reporter: Lars Hofhansl
>            Assignee: Jan Fernando
>         Attachments: PHOENIX-1954-rebased.patch, PHOENIX-1954-wip.patch, PHOENIX-1954-wip2.patch.txt,
PHOENIX-1954-wip3.patch, PHOENIX-1954-wip4.patch, PHOENIX-1954-wip5-rebased.patch, PHOENIX-1954-wip6.patch
>
>
> In order to be able to generate many ids in bulk (for example in map reduce jobs) we
need a way to generate or reserve large sets of ids. We also need to mix ids reserved with
incrementally generated ids from other clients. 
> For this we need to atomically increment the sequence and return the value it had when
the increment happened.
> If we're OK to throw the current cached set of values away we can do
> {{NEXT VALUE FOR <seq>(,<N>)}}, that needs to increment value and return
the value it incremented from (i.e. it has to throw the current cache away, and return the
next value it found at the server).
> Or we can invent a new syntax {{RESERVE VALUES FOR <seq>, <N>}} that does
the same, but does not invalidate the cache.
> Note that in either case we won't retrieve the reserved set of values via {{NEXT VALUE
FOR}} because we'd need to be idempotent in our case, all we need to guarantee is that after
a call to {{RESERVE VALUES FOR <seq>, <N>}}, which returns a value <M> is
that the range [M, M+N) won't be used by any other user of the sequence. My might need reserve
1bn ids this way ahead of a map reduce run.
> Any better ideas?



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