[hibernate-issues] [Hibernate-JIRA] Commented: (HHH-4871) Improve Javadoc (and possibly other) documentation for org.hibernate.id.SequenceHiLoGenerator

[Strong Liu (JIRA)]

    [ http://opensource.atlassian.com/projects/hibernate/browse/HHH-4871?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=35466#action_35466 ] 

Strong Liu commented on HHH-4871:
---------------------------------

if you have a patch, i'd like apply it to trunk, thx

> Improve Javadoc (and possibly other) documentation for org.hibernate.id.SequenceHiLoGenerator
> ---------------------------------------------------------------------------------------------
>
>                 Key: HHH-4871
>                 URL: http://opensource.atlassian.com/projects/hibernate/browse/HHH-4871
>             Project: Hibernate Core
>          Issue Type: Task
>          Components: documentation
>            Reporter: Aleksander Adamowski
>
> The org.hibernate.id.SequenceHiLoGenerator identifier generator is probably the most misunderstood generator due to poor documentation. Unfortunately, it's also the default for JPA, and this leads to serious problems for many people.
> See e.g.:
> ANN-354
> this forum thread: https://forum.hibernate.org/viewtopic.php?f=9&t=967338&view=next
> Many misunderstandings would be avoided, if Javadoc for the org.hibernate.id.SequenceHiLoGenerator class would specify how exactly does the logic work and how should people get the most frequently desired behaviour of ordinary 1:1 sequence from the database (the answer being, use allocationSize=1).
> A good, but generic description of how hi/lo algorithm works is on stack overflow: http://stackoverflow.com/questions/282099/whats-the-hi-lo-algorithm
> The Hibernate's implementation, when used from a @SequenceGenerator, seems to get a hi value from corresponding database sequence, create an initial identifier by multiplying it by allocationSize, then works up from that, incrementing by 1 until the allocation is depleted - then it repeats the procedure by getting a new fresh sequence value, multiplying it etc.
> The docs should also explain how this strategy is beneficial to performance in distributed environments and why it has been chosen as the default over simple 1:1 sequence handling.

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