[jira] [Assigned] (IGNITE-19394) RW index scan may skip entries because of GC

["Ivan Bessonov (Jira)" <ji...@apache.org>]

     [ https://issues.apache.org/jira/browse/IGNITE-19394?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]

Ivan Bessonov reassigned IGNITE-19394:
--------------------------------------

    Assignee: Ivan Bessonov

> RW index scan may skip entries because of GC
> --------------------------------------------
>
>                 Key: IGNITE-19394
>                 URL: https://issues.apache.org/jira/browse/IGNITE-19394
>             Project: Ignite
>          Issue Type: Bug
>            Reporter: Ivan Bessonov
>            Assignee: Ivan Bessonov
>            Priority: Major
>              Labels: ignite-3
>
> The problem is in a peek cursor contract.
> Right now, SortedIndexLocker#acquireLockNextKey assumes that if "peek" returned a value with successfully acquired lock, "next" will iterate over the same value.
> This is not true, if the result of "peek" call was removed by GC. In such case, "next" will actually skip the real next value, that should have been returned to the user.
> We must introduce a new invariant - "hasNext" and "next" always take into account latest result of "peek", it it's been called *after* previous "hasNext"/"next". This will fix the bug.
> Tricky concurrent test required.
> h4. Tangent issues
> Two consecutive calls of "peek", before and after the lock, make us scan index twice. Not sure if there's an easy way to reduce the amount of reads though.
> Also, RW and RO cursors should probably be implemented differently, forcing all these features into a single implementation is nonsense. RO cursor should never peek anything, it may even throw an exception. This will allow it to have internal cache, for example, making it much more efficient.



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