[jira] [Commented] (PHOENIX-1954) Reserve chunks of numbers for a sequence

["James Taylor (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/PHOENIX-1954?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14613531#comment-14613531 ] 

James Taylor commented on PHOENIX-1954:
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I'll take a closer look, but the sort of the List<SequenceKey> is important as it makes for a predictable lock order (preventing potential deadlocks). I'd recommend either creating a new Object or using a List<Pair<SequenceKey,Long>> where the Long is the numToAllocate value so they stay together on the sort. Probably a new SequenceInfo class (or some such name) that stores both SequenceKey and numToAllocate is a little more clear IMHO.

> 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-wip.patch, PHOENIX-1954-wip2.patch.txt
>
>
> 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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