Following your instructions, I also enabled map output compression.
I tried different queries but I couldn't get the benefit from compression
in any single of them. I also tried creating queries which have large
intermediate data, but it didn't improve the performance for them either.
I should also note that our Hadoop cluster is setup at few Amazon EC2
Question is: What are the scenarios in which compression can improve the
On Sat, Oct 6, 2012 at 6:32 PM, Bejoy KS <[EMAIL PROTECTED]> wrote:
> Hi Hadi
> The propertis you specified doen't enable compression of map output. To
> enable map output compression you need to enable the following properties
> SET hive.exec.compress.output=true;
> SET mapred.map.output.compression=true;
> This property 'hive.exec.compress.intermediate
> ' Is used to enable compression of data in between multiple mapreduce jobs
> generated by a hive query.
> Bejoy KS
> Sent from handheld, please excuse typos.
> *From: * Hadi Moshayedi <[EMAIL PROTECTED]>
> *Date: *Sat, 6 Oct 2012 16:55:47 +0300
> *To: *<[EMAIL PROTECTED]>
> *ReplyTo: * [EMAIL PROTECTED]
> *Subject: *Compression of Intermediate Data
> I wanted to look into improving performance of my Hive cluster, and from
> what I read turning on compression of intermediate data could help. As I
> understand, this would help because it would reduce the amount of data
> written to disk in between jobs.
> I look at the documentation and set the following settings:
> SET hive.exec.compress.intermediate=true;
> SET mapred.output.compression.type=BLOCK;
> I ran some queries to see how compression impacts the performance. But it
> usually made the query time worse. I also had a query whose size of
> intermediate data was close to the size of input data, but it made the
> performance worse for this query too.
> Question 1: Are the above settings correct settings for using compression
> of intermediate data?
> Question 2: Are there use-cases in which compression of intermediate data
> would not help performance? Why would someone not keep it turned on always?