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From Yufan Liu <yli...@kent.edu>
Subject Re: Problem in finding the largest value of an indexed column
Date Wed, 01 Jul 2015 21:34:24 GMT
When I made more tests, I find that this problem happens after table got
split.

Here is the DDL I use to create table and index:
CREATE TABLE IF NOT EXISTS t1 (
uid BIGINT NOT NULL,
timestamp BIGINT NOT NULL,
eventName VARCHAR
CONSTRAINT my_pk PRIMARY KEY (uid,  timestamp)) COMPRESSION='SNAPPY';

CREATE INDEX timestamp_index ON t1 (timestamp) INCLUDE (eventName)

Attach is the sample data I used for test. It has about 4000 rows, when the
timestamp_index table has one region, the query returns correct result:
1433334048443, but when I manually split it into 4 regions (use hbase
tool), it returns 1433333024961.

Let know if you find anything. Thanks!


2015-07-01 11:27 GMT-07:00 James Taylor <jamestaylor@apache.org>:

> If you could put a complete test (including your DDL and upsert of data),
> that would be much appreciated.
> Thanks,
> James
>
> On Wed, Jul 1, 2015 at 11:20 AM, Yufan Liu <yliu33@kent.edu> wrote:
>
>> I have tried to use query "SELECT timestamp FROM t1 ORDER BY timestamp
>> DESC NULLS LAST LIMIT 1". But it still returns the same unexpected result.
>> There seems to be some internal problems related.
>>
>> 2015-06-30 18:03 GMT-07:00 James Taylor <jamestaylor@apache.org>:
>>
>>> Yes, reverse scan will be leveraged when possible. Make you use NULLS
>>> LAST in your ORDER BY as rows are ordered with nulls first.
>>>
>>> On Tue, Jun 30, 2015 at 5:25 PM, Yufan Liu <yliu33@kent.edu> wrote:
>>>
>>>> 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
>>>>
>>>>
>>>
>>
>>
>> --
>> best,
>> Yufan
>>
>>
>


-- 
best,
Yufan

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