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From Vladimir Rodionov <vladrodio...@gmail.com>
Subject Re: Phoenix performance efficient problem?
Date Tue, 03 Jun 2014 05:04:38 GMT
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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