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From "Jesse Yates (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (PHOENIX-1954) Reserve chunks of numbers for a sequence
Date Tue, 12 May 2015 21:55:00 GMT

    [ https://issues.apache.org/jira/browse/PHOENIX-1954?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14540851#comment-14540851
] 

Jesse Yates commented on PHOENIX-1954:
--------------------------------------

I'm ok with {{NEXT <n> VALUE FOR <seq>}} as long as we are explicit about what
happens in the case:
{code}
NEXT VALUE FOR <seq>
NEXT 100 VALUE FOR <seq>
NEXT VALUE FOR <seq>
{code}
Which would be something like: 1, 101, 201. Essentially throwing away the "cache" from the
first next value for (which was 1-100), assigning the batch the next 100ids (100-200), and
then getting the next sequential ID (201) with a cache (201-301).

> Reserve chunks of numbers for a sequence
> ----------------------------------------
>
>                 Key: PHOENIX-1954
>                 URL: https://issues.apache.org/jira/browse/PHOENIX-1954
>             Project: Phoenix
>          Issue Type: Bug
>            Reporter: Lars Hofhansl
>
> 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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