Thank you James.
I am using Phoenix 4.5.1 with HBase-0.98.14.
I am also noticing that if WHERE clause returns a fewer number of records, then
ORDER BY with LIMIT works fine. Does this input help in any way?
I will file a CR.
Thanks again,Sumit
From: James Taylor <[email protected]>
To: user <[email protected]>; Sumit Nigam <[email protected]>
Sent: Thursday, December 10, 2015 11:34 PM
Subject: Re: Help with LIMIT clause
Hi Sumit,I agree, these two queries should return the same result, as long as
you have the ORDER BY clause. What version of Phoenix are you using? What does
your DDL look like? Please file a JIRA that ideally includes a way of
reproducing the issue.
select current_timestamp from TBL order by current_timestamp desc limit
1;select max(current_timestamp) from TBL;
Thanks,James
On Thu, Dec 10, 2015 at 8:58 AM, Sumit Nigam <[email protected]> wrote:
In thinking a bit more about it, this should be a bug in Phoenix. This is
because even with LIMIT clause I have a order by timestamp DESC, which means
that column values MUST have been sorted prior to applying LIMIT clause. The
LIMIT should then give a MAX value in such a case. Also, surprisingly this only
seems to be failing in cases where there are huge number of records. Like, in
my case I have 200K + records.
Any help will be appreciated.
Thanks,Sumit
From: Sumit Nigam <[email protected]>
To: Users Mail List Phoenix <[email protected]>
Sent: Thursday, December 10, 2015 8:05 PM
Subject: Help with LIMIT clause
Hi,
The link for salted tables https://phoenix.apache.org/salted.html mentions
"Since salting table would not store the data sequentially, a strict sequential
scan would not return all the data in the natural sorted fashion. Clauses that
currently would force a sequential scan, for example, clauses with LIMIT, would
likely to return items that are different from a normal table"
So, would a simple query such as SELECT CURRENT_TIMESTAMP FROM TBL ORDER BY
CURRENT_TIMESTAMP DESC LIMIT 1; not really return the MAX(CURRENT_TIMESTAMP) ?
PK is on 2 columns with CURRENT_TIMESTAMP as the leading one. I am noticing
this issue:
select current_timestamp from TBL order by current_timestamp desc limit
1;+------------------------------------------+| CURRENT_TIMESTAMP
|+------------------------------------------+| 1448815328556
|+------------------------------------------+
select max(current_timestamp) from
TBL;+------------------------------------------+|
MAX("CURRENT_TIMESTAMP") |+------------------------------------------+|
1449732792090
|+------------------------------------------+
The results are different. MAX is of course, returning the right record.
If this is the case, then what should be done where LIMIT is really to be used?
What can I replace it with to get the desired behavior?
Is this also correct that when there is a WHERE clause limiting the number of
projected records, then LIMIT seems to work fine? I seem to be noticing that
also.
This is with hbase 0.98.14 and phoenix 4.5.x
Thanks,Sumit
