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From Pham Phuong Tu <tuphamphu...@gmail.com>
Subject Re: Phoenix performance efficient problem?
Date Tue, 03 Jun 2014 08:01:22 GMT
Thanks,

Phonenix index lindex by the way create another table wich have same number
of row with indexed table.


2014-06-03 12:04 GMT+07:00 Vladimir Rodionov <vladrodionov@gmail.com>:

> Nope, your second query fetches 6M rows. 20M total rows in a table, one
> column is random int between 0 ..1000, you select all rows with column >
> 700 - 30% of a total which is 20M * 0.3 = 6M
>
>
> On Mon, Jun 2, 2014 at 9:43 PM, Pham Phuong Tu <tuphamphuong@gmail.com>
> wrote:
>
>> Hi Vladimir Rodionov,
>>
>> You are righ when explain the selectivity when we do not use index . But
>> when use index, this query fetch, count with only 300 row, it take 10
>> second !
>>
>>
>>
>>
>>
>> 2014-06-03 11:35 GMT+07:00 Vladimir Rodionov <vladrodionov@gmail.com>:
>>
>> First query selectivity is 1:1000 = 0.1%
>>> Second is 300/1000 = 30%
>>>
>>> This pretty much explains performance difference.
>>>
>>> Try :
>>> select count(*) from test where int_1 > 999
>>>
>>>
>>> On Mon, Jun 2, 2014 at 9:20 PM, Pham Phuong Tu <tuphamphuong@gmail.com>
>>> wrote:
>>>
>>>> HI guys,
>>>>
>>>> I have a test table with 20M rows, one row have 2 column type integer,
>>>> 1 column have index, other dont't have. Value of integer column is random
>>>> value from 0 to 1000.
>>>>
>>>> Run query with equal condition below, query in column with index is
>>>> much faster.
>>>> "select count(*) from test where int_1 = 100;"
>>>> (0.084 seconds vs 15.221 seconds) => > 150x faster
>>>>
>>>> But when run a range query, query in column with index is not much
>>>> faster.
>>>> "select count(*) from test where int_1 > 700;"
>>>> (7.852 seconds vs 12.889 seconds) => > 0.5x faster
>>>>
>>>> Should index have to optimize data organizaion or algorithm to increase
>>>> performance ?
>>>>
>>>> Thanks a lot.
>>>>
>>>>
>>>
>>
>

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