[jira] [Commented] (PHOENIX-1422) Stateless Sequences

["Andrew Purtell (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/PHOENIX-1422?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14240420#comment-14240420 ] 

Andrew Purtell commented on PHOENIX-1422:
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Hybrid Logical Clock (http://muratbuffalo.blogspot.com/2014/07/hybrid-logical-clocks.html) might be a good approach for generating stateless sequences. It looks like a HLC logical timestamps monotonic and fit in 64 bits:
{quote}
We can have a compact representation of HLC timestamps using l and c. NTP uses 64-bit timestamps which consist of a 32-bit part for seconds and a 32-bit part for fractional second. We restrict l to track only the most significant 48 bits of pt. Rounding up pt values to 48 bits l values still gives us microsecond granularity tracking of pt. 16 bits remain for c and allows it room to grow up to 65536. (In our experiments c mostly stayed in single digits.)
{quote}


> Stateless Sequences
> -------------------
>
>                 Key: PHOENIX-1422
>                 URL: https://issues.apache.org/jira/browse/PHOENIX-1422
>             Project: Phoenix
>          Issue Type: Improvement
>            Reporter: Lars Hofhansl
>
> [~apurtell] and I were chatting yesterday.
> It would be good if Phoenix had stateless sequences, i.e. sequences that give out unique ids with (very) high probability.
> We can do that by starting with a timestamp, shifting it left 16 or 24 bits left and fill in the new bits with a random number.
> So we're guaranteed to get a new id for each millisecond and within a millisecond we break the tie with a random number. If we can make the likelihood of duplicate numbers lower than (say) a data center failure, we're OK. I would test this with a upsert into x ... select from x ... type query inserting 100's of millions of rows.
> Need to think of a syntax too.



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