I thought it was optional whether hive stored blocks (up to 1MB?) or records.
If records, it's not storing individual records?
Am I misunderstanding?
Maybe I should get off my lazy butt and just check the source code... ;^)
- Tim.
________________________________________
From: bejoy.had...@gmail.com [bejoy.had...@gmail.com]
Sent: Monday, January 09, 2012 1:22 PM
To: common-user@hadoop.apache.org
Subject: Re: has bzip2 compression been deprecated?
Hi Tim
When you say in hive a table data is compressed by using LZO or so. It
means the file/blocks that contains the records/data are compressed using LZO.
The size would be same as the size of file/blocks in hdfs. It is not like
records are stored as individual blocks in hive. Hive is just a query parser
that parse SQL like queries into MR jobs and run the same on data that lies in
HDFS.
When you a have larger chained jobs generated with multiple QLs you may end up
in more number of small files. There you may go in for enabling merge in hive
to get sufficiently larger files by merging thE smaller files as the final
output from your queries. This would be better for subsequent MR jobs that
operate on the output as well as optimal storage.
Hope it helps!..
Regards
Bejoy K S
-----Original Message-----
From: Tim Broberg <tim.brob...@exar.com>
Date: Mon, 9 Jan 2012 12:27:47
To: common-user@hadoop.apache.org<common-user@hadoop.apache.org>
Reply-To: common-user@hadoop.apache.org
Subject: RE: has bzip2 compression been deprecated?
Out of curiousity, when hive records are compressed, how large is a typical
compressed record?
Do you have issues where the block size is too small to be compressed
efficiently?
More generally, I wonder what the smallest desirable compressed record size is
in the hadoop universe.
- Tim.
________________________________________
From: Tony Burton [tbur...@sportingindex.com]
Sent: Monday, January 09, 2012 10:02 AM
To: common-user@hadoop.apache.org
Subject: RE: has bzip2 compression been deprecated?
Thanks Bejoy - I'm fairly new to Hive so may be wrong here, but I was under the
impression that the STORED AS part of a CREATE TABLE in Hive refers to how the
data in the table will be stored once the table is created, rather than the
compression format of the data used to populate the table. Can you clarify
which is the correct interpretation? If it's the latter, how would I read a
sequence file into a Hive table?
Thanks,
Tony
-----Original Message-----
From: Bejoy Ks [mailto:bejoy.had...@gmail.com]
Sent: 09 January 2012 17:33
To: common-user@hadoop.apache.org
Subject: Re: has bzip2 compression been deprecated?
Hi Tony
Adding on to Harsh's comments. If you want the generated sequence
files to be utilized by a hive table. Define your hive table as
CREATE EXTERNAL TABLE tableNAme(col1 INT, c0l2 STRING)
...
...
....
STORED AS SEQUENCEFILE;
Regards
Bejoy.K.S
On Mon, Jan 9, 2012 at 10:32 PM, alo.alt <wget.n...@googlemail.com> wrote:
> Tony,
>
> snappy is also available:
> http://code.google.com/p/hadoop-snappy/
>
> best,
> Alex
>
> --
> Alexander Lorenz
> http://mapredit.blogspot.com
>
> On Jan 9, 2012, at 8:49 AM, Harsh J wrote:
>
> > Tony,
> >
> > * Yeah, SequenceFiles aren't human-readable, but "fs -text" can read it
> out (instead of a plain "fs -cat"). But if you are gonna export your files
> into a system you do not have much control over, probably best to have the
> resultant files not be in SequenceFile/Avro-DataFile format.
> > * Intermediate (M-to-R) files use a custom IFile format these days,
> which is built purely for that purpose.
> > * Hive can use SequenceFiles very well. There is also documented info on
> this in the Hive's wiki pages (Check the DDL pages, IIRC).
> >
> > On 09-Jan-2012, at 9:44 PM, Tony Burton wrote:
> >
> >> Thanks for the quick reply and the clarification about the
> documentation.
> >>
> >> Regarding sequence files: am I right in thinking that they're a good
> choice for intermediate steps in chained MR jobs, or for file transfer
> between the Map and the Reduce phases of a job; but they shouldn't be used
> for human-readable files at the end of one or more MapReduce jobs? How
> about if the only use a job's output is analysis via Hive - can Hive create
> tables from sequence files?
> >>
> >> Tony
> >>
> >>
> >>
> >> -----Original Message-----
> >> From: Harsh J [mailto:ha...@cloudera.com]
> >> Sent: 09 January 2012 15:34
> >> To: common-user@hadoop.apache.org
> >> Subject: Re: has bzip2 compression been deprecated?
> >>
> >> Bzip2 is pretty slow. You probably do not want to use it, even if it
> does file splits (a feature not available in the stable line of 0.20.x/1.x,
> but available in 0.22+).
> >>
> >> To answer your question though, bzip2 was removed from that document
> cause it isn't a native library (its pure Java). I think bzip2 was added
> earlier due to an oversight, as even 0.20 did not have a native bzip2
> library. This change in docs does not mean that BZip2 is deprecated -- it
> is still fully supported and available in the trunk as well. See
> https://issues.apache.org/jira/browse/HADOOP-6292 for the doc update
> changes that led to this.
> >>
> >> The best way would be to use either:
> >>
> >> (a) Hadoop sequence files with any compression codec of choice (best
> would be lzo, gz, maybe even snappy). This file format is built for HDFS
> and MR and is splittable. Another choice would be Avro DataFiles from the
> Apache Avro project.
> >> (b) LZO codecs for Hadoop, via
> >> https://github.com/toddlipcon/hadoop-lzo(and hadoop-lzo-packager for
> >> packages). This requires you to run indexing
> operations before the .lzo can be made splittable, but works great with
> this extra step added.
> >>
> >> On 09-Jan-2012, at 7:17 PM, Tony Burton wrote:
> >>
> >>> Hi,
> >>>
> >>> I'm trying to work out which compression algorithm I should be using
> in my MapReduce jobs. It seems to me that the best solution is a
> compromise between speed, efficiency and splittability. The only
> compression algorithm to handle file splits (according to Hadoop: The
> Definitive Guide 2nd edition p78 etc) is bzip2, at the expense of
> compression speed.
> >>>
> >>> However, I see from the documentation at
> http://hadoop.apache.org/common/docs/current/native_libraries.html that
> the bzip2 library is no longer mentioned, and hasn't been since version
> 0.20.0, see
> http://hadoop.apache.org/common/docs/r0.20.0/native_libraries.html -
> however the bzip2 Codec is still in the API at
> http://hadoop.apache.org/common/docs/current/api/org/apache/hadoop/io/compress/BZip2Codec.html
> .
> >>>
> >>> Has bzip2 support been removed from Hadoop, or will it be removed soon?
> >>>
> >>> Thanks,
> >>>
> >>> Tony
> >>>
> >>>
> >>>
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