'LOAD DATA INPATH ..' issues a hdfs move under the hood, that is why the original data in hdfs is not present after the load operation. If you want to preserve the data in some hdfs location and use the same with hive, why not create an external table and point it to the required hdfs location.
From: "[EMAIL PROTECTED]" <[EMAIL PROTECTED]>
To: [EMAIL PROTECTED]
Sent: Wednesday, September 12, 2012 8:55 AM
Subject: RE: Performance: hive+hbase integration query against the row_key
after loading the data into hive tables, the files gets automatically deleted from HDFS...how to stop that?
From: Alan Gates [mailto:[EMAIL PROTECTED]]
Sent: 12 September 2012 06:51
To: [EMAIL PROTECTED]
Subject: Re: Performance: hive+hbase integration query against the row_key
On Sep 11, 2012, at 7:00 AM, bharath vissapragada wrote:
> Hive does all kinds of parsing , metadata lookups, query tree building and stuff before executing the query. Not sure if this all was included in those 36 seconds !
> Also what hive does is, it builds a scan object with ranges based on predicates (and mappers too ) on key column and not a direct "get" call as in hbase shell. This might incur some overhead too!
Since Hive does this in a MapReduce job it definitely incurs overhead. It does not run directly against HBase as you might wish it did here.
> On Tue, Sep 11, 2012 at 7:10 PM, Shengjie Min <[EMAIL PROTECTED]> wrote:
> I am trying to get hive working on top of my hbase table following the guide below:
> CREATE EXTERNAL TABLE hive_hbase_test (key string, a string, b string, c string)
> STORED BY 'org.apache.hadoop.hive.hbase.HBaseStorageHandler'
> WITH SERDEPROPERTIES
> ("hbase.columns.mapping"=":key,cf:a,cf:b,cf:c") TBLPROPERTIES ("hbase.table.name"="test");
> this hive table creation makes my mapping roughly look like this:
> hive_hbase_test VS test
> Hive key - hbase row_key
> Hive column a - hbase cf:a
> Hive column b - hbase cf:b
> Hive column c - hbase cf:c
> From my understanding on how HBaseStorageHandler works, it's supposed to take advantage of the hbase row_key index as much as possible. So I would expect,
> 1. if you do a hive query against the row key like "select * from hive_hbase_test where key='blabla'", this would utilize the hbase row_key index which give you very quick nearly real-time response just like hbase does.
> 2. of coz, if you do a hive query against a column like "select * from hive_hbase_test where a='blabla'", in this case, it queries against a specific column, it probably uses mapred because there is nothing from Hbase side can be utilized.
> From my test, query 1 doesn't seem fast at all, still taking ages, so
> select * from hive_hbase_test where key='blabla' 36secs
> get 'test', 'blabla' less than 1 sec
> still shows a huge difference.
> Anybody has tried this before? Is there anyway I can do sort of query plan analysis against hive query? or I am not mapping hive table against hbase table correctly?
> All the best,
> Shengjie Min
> Bharath .V
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