Thanks, Steven.
So, am I correct in understanding that even the sorting columns
(user_id, time in my example) would not be used to optimize the query
shown below?
On 11-09-09 07:00 PM, Steven Wong wrote:
Bucketing only speeds up sampling queries. Hive doesn't know/remember the hash
function(s) you use to bucket the data, so it cannot use that to speed up
lookups by a bucketed column.
-----Original Message-----
From: Mark Grover [mailto:mgro...@oanda.com]
Sent: Friday, September 09, 2011 4:18 AM
To: user@hive.apache.org
Cc: Travis Powell; Baiju Devani; Bob Tiernay
Subject: Re: Best practices for storing data on Hive
Edward, Steven or anyone else on the mailing list:
Is it possible to optimize queries like the one below with bucketing?
select * from<table> where user_id='blah' and dt>= '2011-05-26' and dt<=
'2011-05-28';
where<table> is partitioned by dt (which represents day), bucketed by user_id
and within each bucket data is sorted by user_id, time.
The Hive wiki says, that bucketing can improve performance on certain kinds of
queries. What kinds of queries are these?
Only Sampling queries? Group by on bucketed column? Where clause on bucketed
column? All of the above?
Thanks in advance!
Mark
----- Original Message -----
From: "Edward Capriolo"<edlinuxg...@gmail.com>
To: user@hive.apache.org
Cc: "Travis Powell"<tpow...@tealeaf.com>, "Baiju Devani"<bdev...@oanda.com>, "Bob
Tiernay"<btier...@oanda.com>
Sent: Thursday, September 8, 2011 9:26:10 PM
Subject: Re: Best practices for storing data on Hive
On Thu, Sep 8, 2011 at 8:30 PM, Steven Wong< sw...@netflix.com> wrote:
I think this statement is not true: "By distributing by (and preferably ordering by)
user_id, we can minimize seek time in the table because Hive knows where all entries
pertaining to a specific user are stored." I think it is not true whether the table
is bucketed on user_id or not (assuming that user_id is not a partition column or indexed
column).
-----Original Message-----
From: Mark Grover [mailto: mgro...@oanda.com ]
Sent: Tuesday, September 06, 2011 2:36 PM
To: user@hive.apache.org
Cc: Travis Powell; Baiju Devani; Bob Tiernay
Subject: Re: Best practices for storing data on Hive
Thanks for your reply, Travis.
I was under the impression that for Hive to make use of sorted structure
of data (i.e. for the table named "data" in your example), the metadata
of the table (specified during table creation) has to advertise such
property. However, I don't see any special metadata specifying such
property when "data" table was created.
Is that true? If so, is such metadata specified by using CLUSTERED BY
and SORTED BY clauses during table creation?
On 11-09-06 03:50 PM, Travis Powell wrote:
Hi Mark,
When we load data into Hive, we use a staging table to dynamically partition
our data. This might help you too.
We create our initial table and our staging table:
DROP TABLE IF EXISTS staging_data;
CREATE TABLE staging_data ( ... )
ROW FORMAT DELIMITED FIELDS TERMINATED BY ',';
CREATE TABLE data ( ... )
PARTITIONED BY (dt STRING, hour, INT)
ROW FORMAT DELIMITED FIELDS TERMINATED BY ',' STORED AS SEQUENCEFILE;
INSERT OVERWRITE TABLE data PARTITION(dt, hour) SELECT q.*,
to_date(q.session_timestamp) AS dt, hour(q.session_timestamp) AS hour FROM
staging_session q ORDER BY user_id DISTRIBUTE BY user_id;
So.....
By distributing by (and preferably ordering by) user_id, we can minimize seek
time in the table because Hive knows where all entries pertaining to a specific
user are stored. Partitions by time have the best performance, because chances
are almost every query will have some time-related component in it (and it
spreads out the data among partitions fairly well.)
Let me know if this works for you. We start every job with those first few
lines of Hive script. It works well for us.
Thanks,
Travis Powell
-----Original Message-----
From: Mark Grover [mailto: mgro...@oanda.com ]
Sent: Tuesday, September 06, 2011 12:39 PM
To: user@hive.apache.org
Cc: wd; Bob Tiernay; Baiju Devani
Subject: Re: Best practices for storing data on Hive
Thanks for the response, wd.
I would REALLY APPRECIATE if other people can share their views as well.
Here are the possible solutions that I have thought about to the problem
(see original email for description of problem):
1) Multiple partitions: We would partition the table by day and userId.
However, given the amount of users that visit our website (hundreds of
thousands of unique users every day), this would lead to a large number
of partitions (and rather small file sizes, ranging from a couple of
bytes to a couple of KB). From the documentation I've read online, it
seems that Hive/Hadoop weren't designed to deal with such small file
sizes and such a situation should be avoided if possible.
We had a scenario previously where we were partitioning by day and hour
and because of the sheer number of partitions queries like "select *
from<table> LIMIT 1;" were taking very long and even failed because of
"Java out of Heap space" errors. My guess is that the master node was
munching through all these partitions and couldn't deal with the large
number of partitions.
2) Use of data locality: We could keep the data partitioned by day and
bucketed by userId. Within each bucket sort the data by the (userId,
time). This way we could keep the data related to each userId together
within a daily partition and if Hive could be made aware of this sorting
order and could make use of this order to improve search/query times,
that would alleviate the problem quite a bit. The big question here is:
Does Hive leverage sorting order of data within a partition bucket when
running (most/all?) queries, where possible?
3) Using an index: As wd mentioned, Hive 0.7 introduces the notion on an
index. If I do index on userId, given that we can hundreds of thousands
of unique users per day, would indexing prove to be a good move? Are
there people who are using it for similar purposes or on a similar scale?
4) Using 2 "orthogonal tables": As mentioned in my original email (see
below), we could have 2 independent tables, one which stores data
partitioned by day and other partitioned by userId. For maintaining
partitions in userId partitioned table, I am planning to do the following:
In the nightly job, if userId=X visited the website previous day, we
create a partition for userId=X if it doesn't already exist. Once the
partition is created, all clicks for that user Id on the day for in
question are put in a single file and dropped in the userId=X folder on
HDFS. This method could be used to simulate an "append" to the Hive
table. The file would only be a few bytes to a few KB and the format of
the table would be sequence file.
What are your thoughts about the above 4 methods? Any particular likes
or dislikes? Any comments, suggestions would be helpful.
Thank you again in advance!
Mark
On 11-09-04 04:01 AM, wd wrote:
Hive support more than one partitions, have your tried? Maybe you can
create to partitions named as date and user.
Hive 0.7 also support index, maybe you can have a try.
On Sat, Sep 3, 2011 at 1:18 AM, Mark Grover< mgro...@oanda.com> wrote:
Hello folks,
I am fairly new to Hive and am wondering if you could share some of the best
practices for storing/querying data with Hive.
Here is an example of the problem I am trying to solve.
The traffic to our website is logged in files that contain information about
clicks from various users.
Simplified, the log file looks like:
t_1, ip_1, userid_1
t_2, ip_2, userid_2
t_3, ip_3, userid_3
...
where t_i represents time of the click, ip_i represents ip address where the
click originated from, and userid_i represents the user ID of the user.
Since the clicks are logged on an ongoing basis, partitioning our Hive table by
day seemed like the obvious choice. Every night we upload the data from the
previous day into a new partition.
However, we would also want the capability to find all log lines corresponding
to a particular user. With our present partitioning scheme, all day partitions
are searched for that user ID but this takes a long time. I am looking for
ideas/suggestions/thoughts/comments on how to reduce this time.
As a solution, I am thinking that perhaps we could have 2 independent tables,
one which stores data partitioned by day and the other partitioned by userId.
With the second table partitioned by userId, I will have to find some way of
maintaining the partitions since Hive doesn't support appending of files. Also,
this seems suboptimal, since we are doubling that the amount of data that we
store. What do you folks think of this idea?
Do you have any other suggestions on how we can approach this problem?
What have other people in similar situations done? Please share.
Thank you in advance!
Mark
--
Mark Grover, Business Intelligence Analyst
OANDA Corporation
www: oanda.com www: fxtrade.com
e: mgro...@oanda.com
"Best Trading Platform" - World Finance's Forex Awards 2009.
"The One to Watch" - Treasury Today's Adam Smith Awards 2009.
