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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 Tue, 11 Aug 2015 17:45:45 GMT

    [ https://issues.apache.org/jira/browse/HIVE-11500?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14682158#comment-14682158
] 

Alan Gates commented on HIVE-11500:
-----------------------------------

I am guessing that this will be the first of several things we'd like to cache in the metastore.
 Rather than build specific calls in the already seriously bloated RawStore interface for
each type of cache would it be possible to build an interface something like this in the metastore:

{code}
interface CacheFilter { boolean include(String key, byte[] value); }
putInCache(String cacheName, String key, byte[] serializedProtoBuf);
getFromCache(String cacheName, String key);
getFromCacheWithFilter(String cacheName, CacheFilter filter);
deleteFromCache(String cacheName, String key);
{code}

On the ACID incompatibility, is it just because of PPD not working with ACID?  There is a
plan to address that soon.  If there's more than that we need to discuss and see how to resolve
this.

On cache cleaning, how can the cleaner now when an entry is stale?  We should be able to use
the active threads in the ACID compactor to do tasks like cache cleaning and caching new entries.

> 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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