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From "James Taylor (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (PHOENIX-1954) Reserve chunks of numbers for a sequence
Date Mon, 11 May 2015 21:03:00 GMT

    [ https://issues.apache.org/jira/browse/PHOENIX-1954?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14538641#comment-14538641
] 

James Taylor commented on PHOENIX-1954:
---------------------------------------

bq. What happens if you use {{NEXT VALUE FOR seq}} more than one place in the same SQL statement?

Good question. I was thinking to have all occurrences in the same statement to the same sequence
return the same sequence value  (that's what we do today) regardless of how many they're allocating.
Perhaps we can just use the max allocation we see.

I like your idea for the syntax better than mine (one less new keyword). Would this be feasible
to support in Calcite?

> 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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