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From Alan Gates <ga...@yahoo-inc.com>
Subject Re: asking for comments on benchmark queries
Date Tue, 23 Jun 2009 17:31:42 GMT

I don't think you're subscribed to pig-dev (your emails have been  
bouncing to the moderator).  So I've cc'd you explicitly on this.

I don't think we need a Pig JIRA, it's probably easier if we all work  
on the hive one.  I'll post my comments on the various scripts to that  
bug.  I've also attached them here since pig-dev won't see the updates  
to that bug.



Adding types in the LOAD statement will force Pig to cast the key  
field, even though it doesn't need to (it only reads and writes the  
key field).  So I'd change the query to be:

rmf output/PIG_bench/grep_select;
a = load '/data/grep/*' using PigStorage as (key,field);
b = filter a by field matches '.*XYZ.*';
store b into 'output/PIG_bench/grep_select';

field will still be cast to a chararray for the matches, but we won't  
waste time casting key and then turning it back into bytes for the  


Same comment, remove the casts.  pagerank will be properly cast to an  

rmf output/PIG_bench/rankings_select;
a = load '/data/rankings/*' using PigStorage('|') as  
b = filter a by pagerank > 10;
store b into 'output/PIG_bench/rankings_select';


Here you want to keep the casts of pagerank so that it is handled as  
the right type.  adRevenue will default to double in SUM when you  
don't specify a type.  You also want to project out all unneeded  
columns as soon as possible.  You should set PARALLEL on the join to  
use the number of reducers appropriate for your cluster.  Given that  
you have 10 machines and 5 reduce slots per machine, and speculative  
execution is off you probably want 50 reducers.  I notice you set  
parallel to 60 on the group by.  That will give you 10 trailing  
reducers.  Unless you have a need for the result to be split 60 ways  
you should reduce that to 50 as well.  (I'm assuming here when you say  
you have a 10 node cluster you mean 10 data nodes, not counting your  
name node and task tracker.  The reduce formula should be 5 * number  
of data nodes.)

A last question is how large are the uservisits and rankings data  
sets?  If either is < 80M or so you can use the fragment/replicate  
join, which is much faster than the general join.  The following  
script assumes that isn't the case; but if it is let me know and I can  
show you the syntax for it.

So the end query looks like:

rmf output/PIG_bench/html_join;
a = load '/data/uservisits/*' using PigStorage('|') as
b = load '/data/rankings/*' using PigStorage('|') as  
c = filter a by visitDate > '1999-01-01' AND visitDate < '2000-01-01';
c1 = fjjkkoreach c generate sourceIP, destURL, addRevenue;
b1 = foreach b generate pagerank, pageurl;
d = JOIN c1 by destURL, b1 by pageurl parallel 50;
d1 = foreach d generate sourceIP, pagerank, adRevenue;
e = group d1 by sourceIP parallel 50;
f = FOREACH e GENERATE group, AVG(d1.pagerank), SUM(d1.adRevenue);
store f into 'output/PIG_bench/html_join';


Same comments as above on projecting out as early as possible and on  
setting parallel appropriately for your cluster.

rmf output/PIG_bench/uservisits_aggre;
a = load '/data/uservisits/*' using PigStorage('|') as
a1 = foreach a generate sourceIP, adRevenue;
b = group a by sourceIP parallel 50;
c = FOREACH b GENERATE group, SUM(a. adRevenue);
store c into 'output/PIG_bench/uservisits_aggre';

On Jun 22, 2009, at 10:36 PM, Zheng Shao wrote:

> Hi Pig team,
> We’d like to get your feedback on a set of queries we implemented on  
> Pig.
> We’ve attached the hadoop configuration and pig queries in the  
> email. We start the queries by issuing “pig xxx.pig”. The queries  
> are from SIGMOD’2009 paper. More details are athttps:// 
> issues.apache.org/jira/browse/HIVE-396 (Shall we open a JIRA on PIG  
> for this?)
> One improvement is that we are going to change hadoop to use LZO as  
> intermediate compression algorithm very soon. Previously we used  
> gzip for all performance tests including hadoop, hive and pig.
> The reason that we specify the number of reducers in the query is to  
> try to match the same number of reducer as Hive automatically  
> suggested. Please let us know what is the best way to set the number  
> of reducers in Pig.
> Are there any other improvements we can make to the Pig query and  
> the hadoop configuration?
> Thanks,
> Zheng
> <hadoop-site.xml><hive-default.xml><hadoop-env.sh.txt>

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