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From "Alan Gates (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HIVE-11500) implement file footer / splits cache in HBase metastore
Date Fri, 14 Aug 2015 16:57:45 GMT

    [ https://issues.apache.org/jira/browse/HIVE-11500?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14697368#comment-14697368
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Alan Gates commented on HIVE-11500:
-----------------------------------

bq. I think we should use YAGNI principle...
That's fine, but it means on the next interface you want to add you have to convince me that
you should add another set of calls rather than refactor this one to be generic.

bq.  Having many methods on metastore is not really that big of a deal, since they do different
things.
I disagree.  Having just implemented a new version of RawStore I can tell you that it took
me a long time to understand the nuances of why there's five different ways to fetch partitions.
 I'm still not sure I have it all straight.  We should not just add a new call each time because
it's the shortest path to get the new thing working.  We need to think about code maintenance
and understandability for future developers.

> implement file footer / splits cache in HBase metastore
> -------------------------------------------------------
>
>                 Key: HIVE-11500
>                 URL: https://issues.apache.org/jira/browse/HIVE-11500
>             Project: Hive
>          Issue Type: Sub-task
>          Components: Metastore
>            Reporter: Sergey Shelukhin
>            Assignee: Sergey Shelukhin
>         Attachments: HBase metastore split cache.pdf
>
>
> We need to cache file metadata (e.g. ORC file footers) for split generation (which, on
FSes that support fileId, will be valid permanently and only needs to be removed lazily when
ORC file is erased or compacted), and potentially even some information about splits (e.g.
grouping based on location that would be good for some short time), in HBase metastore.
> -It should be queryable by table. Partition predicate pushdown should be supported. If
bucket pruning is added, that too.- Given that we cannot cache file lists (we have to check
FS for new/changed files anyway), and the difficulty of passing of data about partitions/etc.
to split generation compared to paths, we will probably just filter by paths and fileIds.
It might be different for splits
> In later phases, it would be nice to save the (first category above) results of expensive
work done by jobs, e.g. data size after decompression/decoding per column, etc. to avoid surprises
when ORC encoding is very good, or very bad. Perhaps it can even be lazily generated. Here's
a pony: 🐴



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