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From "Sergey Shelukhin (JIRA)" <>
Subject [jira] [Commented] (HIVE-11500) implement file footer / splits cache in HBase metastore
Date Wed, 12 Aug 2015 17:53:45 GMT


Sergey Shelukhin commented on HIVE-11500:

The filter should ideally use deserialized columns.
I am vary of implementing interfaces that are too general, especially since different caches
have different semantics (i.e. footer cache never expires, but split location cache expires),
different return types (as the doc states we may not even return the footer from footer cache
with filter request). I think we should use YAGNI principle and add interfaces as needed unless
we find we actually need a general cache. Then we can design a general cache.
Having many methods on metastore is not really that big of a deal, since they do different
things. The only ones that could be removed are the outdated ones, i.e. where argument method
was replaced by request-response methods, and such

> implement file footer / splits cache in HBase metastore
> -------------------------------------------------------
>                 Key: HIVE-11500
>                 URL:
>             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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