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From Vadim Dedkov <dedko...@gmail.com>
Subject Re: Hive indexes without improvement of performance
Date Thu, 16 Jun 2016 21:55:35 GMT
I explain. I can get result for count(*) with index table help, but I can't
realise how I can get result for *-select with index table help
17 июня 2016 г. 0:50 пользователь "Vadim Dedkov" <dedkovva@gmail.com>
написал:

> >>If the optimizer does not pick up the index then you can query the index
> directly
> Could you explain me, how I can do this for query like
>
> *select * from my_schema_name.doc_t WHERE id = '3723445235879';*
>
> ?
> Thank you
> 17 июня 2016 г. 0:03 пользователь "Jörn Franke" <jornfranke@gmail.com>
> написал:
>
>> The indexes are based on HDFS blocksize, which is usually around 128 mb.
>> This means for hitting a single row you must always load the full block. In
>> traditional databases this blocksize it is much faster. If the optimizer
>> does not pick up the index then you can query the index directly (it is
>> just a table!). Keep in mind that you should use for the index also an
>> adequate storage format, such as Orc or parquet.
>>
>> You should not use the traditional indexes, but use Hive+Tez and the Orc
>> format with storage indexes and bloom filters (i.e. Min Hive 1.2). It is of
>> key importance that you insert the data sorted on the columns that you use
>> in the where clause. You should compress the table with snappy.
>> Additionally partitions make sense. Finally please use the right data types
>> . Storage indexes work best with ints etc. for text fields you can try
>> bloom filters.
>>
>> That being said, also in other relational databases such as Oracle
>> Exadata, the use of traditional indexes is discouraged for warehouse
>> scenarios, but storage indexes and columnar formats including compression
>> will bring the most performance.
>>
>> On 16 Jun 2016, at 22:50, Vadim Dedkov <dedkovva@gmail.com> wrote:
>>
>> Hello!
>>
>> I use Hive 1.1.0-cdh5.5.0 and try to use indexes support.
>>
>> My index creation:
>> *CREATE INDEX doc_id_idx on TABLE my_schema_name.doc_t (id) AS 'COMPACT'
>> WITH DEFERRED REBUILD;*
>> *ALTER INDEX doc_id_idx ON my_schema_name.doc_t REBUILD;*
>>
>> Then I set configs:
>> *set hive.optimize.autoindex=true;*
>> *set hive.optimize.index.filter=true;*
>> *set hive.optimize.index.filter.compact.minsize=0;*
>> *set hive.index.compact.query.max.size=-1;*
>> *set hive.index.compact.query.max.entries=-1; *
>>
>> And my query is:
>> *select count(*) from my_schema_name.doc_t WHERE id = '3723445235879';*
>>
>> Sometimes I have improvement of performance, but most of cases - not.
>>
>> In cases when I have improvement:
>> 1. my query is
>> *select count(*) from my_schema_name.doc_t WHERE id = '3723445235879';*
>> give me NullPointerException (in logs I see that Hive doesn't find my
>> index table)
>> 2. then I write:
>> *USE my_schema_name;*
>> *select count(*) from doc_t WHERE id = '3723445235879';*
>> and have result with improvement
>> (172 sec)
>>
>> In case when I don't have improvement, I can use either
>> *select count(*) from my_schema_name.doc_t WHERE id = '3723445235879';*
>> without exception, either
>> *USE my_schema_name;*
>> *select count(*) from doc_t WHERE id = '3723445235879';*
>> and have result
>> (1153 sec)
>>
>> My table is about 6 billion rows.
>> I tried various combinations on index configs, including only these two:
>> *set hive.optimize.index.filter=true;*
>> *set hive.optimize.index.filter.compact.minsize=0;*
>> My hadoop version is 2.6.0-cdh5.5.0
>>
>> What I do wrong?
>>
>> Thank you.
>>
>> --
>> _______________             _______________
>> Best regards,                    С уважением
>> Vadim Dedkov.                  Вадим Дедков.
>>
>>

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