[jira] [Commented] (HIVE-12995) LLAP: Synthetic file ids need collision checks

["Sergey Shelukhin (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/HIVE-12995?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15131320#comment-15131320 ] 

Sergey Shelukhin commented on HIVE-12995:
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It might be easier to make cache support T as key, then use Long for HDFS and a struct for other FSes. It might ever work with multiple FSes per cache easily, will definitely work with one.

> LLAP: Synthetic file ids need collision checks
> ----------------------------------------------
>
>                 Key: HIVE-12995
>                 URL: https://issues.apache.org/jira/browse/HIVE-12995
>             Project: Hive
>          Issue Type: Bug
>          Components: llap
>    Affects Versions: 2.1.0
>            Reporter: Gopal V
>
> LLAP synthetic file ids do not have any way of checking whether a collision occurs other than a data-error.
> Synthetic file-ids have only been used with unit tests so far - but they will be needed to add cache mechanisms to non-HDFS filesystems.
> In case of Synthetic file-ids, it is recommended that we track the full-tuple (path, mtime, len) in the cache so that a cache-hit for the synthetic file-id can be compared against the parameters & only accepted if those match.



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