phoenix-user mailing list archives

Site index · List index
Message view « Date » · « Thread »
Top « Date » · « Thread »
From Yufan Liu <yli...@kent.edu>
Subject Re: Problem in finding the largest value of an indexed column
Date Wed, 01 Jul 2015 00:25:25 GMT
I used the HBase reverse scan to find the last row on the index table. It
returned the expected result. I would like to know is Phoenix's "ORDER BY"
and "DESC" implemented based on HBase reverse scan?

2015-06-26 17:25 GMT-07:00 Yufan Liu <yliu33@kent.edu>:

> Thank you anyway, Michael!
>
> 2015-06-26 17:21 GMT-07:00 Michael McAllister <mmcallister@homeaway.com>:
>
>>  OK, I’m a Phoenix newbie, so that was the extent of the advice I could
>> give you. There are people here far more experienced than I am who should
>> be able to give you deeper advice. Have a great weekend!
>>
>>
>>
>> Mike
>>
>>
>>
>> *From:* Yufan Liu [mailto:yliu33@kent.edu]
>> *Sent:* Friday, June 26, 2015 7:19 PM
>> *To:* user@phoenix.apache.org
>> *Subject:* Re: Problem in finding the largest value of an indexed column
>>
>>
>>
>> Hi Michael,
>>
>> Thanks for the advice, for the first one, it's "CLIENT 67-CHUNK PARALLEL
>> 1-WAY FULL SCAN OVER TIMESTAMP_INDEX; SERVER FILTER BY FIRST KEY ONLY;
>> SERVER AGGREGATE INTO SINGLE ROW" which is as expected. For the second one,
>> it's "CLIENT 67-CHUNK SERIAL 1-WAY REVERSE FULL SCAN OVER TIMESTAMP_INDEX;
>> SERVER FILTER BY FIRST KEY ONLY; SERVER 1 ROW LIMIT" which looks correct,
>> but still returns the unexpected result.
>>
>>
>>
>> 2015-06-26 16:59 GMT-07:00 Michael McAllister <mmcallister@homeaway.com>:
>>
>> Yufan
>>
>>
>>
>> Have you tried using the EXPLAIN command to see what plan is being used
>> to access the data?
>>
>>
>>
>> Michael McAllister
>>
>> Staff Data Warehouse Engineer | Decision Systems
>>
>> mmcallister@HomeAway.com | C: 512.423.7447 | skype: michael.mcallister.ha
>> <zimmkate@hotmail.com> | webex: https://h.a/mikewebex
>>
>> [image: Description: Description: cid:3410354473_30269081]
>>
>> This electronic communication (including any attachment) is
>> confidential.  If you are not an intended recipient of this communication,
>> please be advised that any disclosure, dissemination, distribution, copying
>> or other use of this communication or any attachment is strictly
>> prohibited.  If you have received this communication in error, please
>> notify the sender immediately by reply e-mail and promptly destroy all
>> electronic and printed copies of this communication and any attachment.
>>
>>
>>
>> *From:* Yufan Liu [mailto:yliu33@kent.edu]
>> *Sent:* Friday, June 26, 2015 6:31 PM
>> *To:* user@phoenix.apache.org
>> *Subject:* Problem in finding the largest value of an indexed column
>>
>>
>>
>> Hi,
>>
>> We have created a table (eg, t1), and a global index of one numeric
>> column of t1 (eg, timestamp). Now we want to find the largest value of
>> timestamp, we have tried two approaches:
>>
>>
>> 1. select max(timestamp) from t1; This query takes forever to finish, so
>> I think it maybe doing a full table scan/comparison .
>>
>> 2. select timestamp from t1 order by timestamp desc limit 1; This query
>> finished fast, but the result it returns is far from the largest value. It
>> seems it just return the largest value for a certain range of data.
>>
>> Did anyone else encounter this issue/have any suggestion?
>>
>>
>> --
>>
>> Thanks,
>>
>> Yufan
>>
>>
>>
>>
>> --
>>
>> best,
>> Yufan
>>
>
>
>
> --
> best,
> Yufan
>
>


-- 
best,
Yufan

Mime
View raw message