Ok so what is the resolution here? My understanding is that bucketing does not improve the performance. Is that correct?
Dr Mich Talebzadeh LinkedIn https://www.linkedin.com/profile/view?id=AAEAAAAWh2gBxianrbJd6zP6AcPCCdOABUrV8Pw Sybase ASE 15 Gold Medal Award 2008 A Winning Strategy: Running the most Critical Financial Data on ASE 15 http://login.sybase.com/files/Product_Overviews/ASE-Winning-Strategy-091908.pdf Author of the books "A Practitioner’s Guide to Upgrading to Sybase ASE 15", ISBN 978-0-9563693-0-7. co-author "Sybase Transact SQL Guidelines Best Practices", ISBN 978-0-9759693-0-4 Publications due shortly: Complex Event Processing in Heterogeneous Environments, ISBN: 978-0-9563693-3-8 Oracle and Sybase, Concepts and Contrasts, ISBN: 978-0-9563693-1-4, volume one out shortly http://talebzadehmich.wordpress.com <http://talebzadehmich.wordpress.com/> NOTE: The information in this email is proprietary and confidential. This message is for the designated recipient only, if you are not the intended recipient, you should destroy it immediately. Any information in this message shall not be understood as given or endorsed by Peridale Technology Ltd, its subsidiaries or their employees, unless expressly so stated. It is the responsibility of the recipient to ensure that this email is virus free, therefore neither Peridale Technology Ltd, its subsidiaries nor their employees accept any responsibility. From: Akansha Jain [mailto:akansha.15au...@gmail.com] Sent: 25 January 2016 22:44 To: user@hive.apache.org Subject: RE: Hive Bucketing Thanks for detailed explanation. Even without bucket pruning, expectation from bucketing is performance improvement. I am joining two tables which are bucketed on same no of buckets and column and comparing the performance with join of two unbucketed tables on bucket led column. I am using mapr dist and map join conversion is enabled by default. Performance is same in both the cases. I increased data size from 120 gb to 400 gb to see clear performance difference. But still results are same. Have set hive.optimize.bucketmapjoin=true. Any clue why that would be happening. Thanks, AJ On Jan 22, 2016 4:31 PM, "Mich Talebzadeh" <m...@peridale.co.uk <mailto:m...@peridale.co.uk> > wrote: Hi, In general my understanding is that it will be possible to use bucket pruning much like partition pruning (elimination) soon Bucketing in Hive refers to hash partitioning where a hashing function is applied. Likewise an RDBMS like Oracle, Hive will apply a linear hashing algorithm to prevent data from clustering within specific partitions. Hashing is very effective if the column selected for bucketing has very high selectivity like an ID column where selectivity (select count(distinct(column))/count(column) ) = 1. In this case, the created partitions/ files will be as evenly sized as possible. In a nutshell bucketing is a method to get data evenly distributed over many partitions/files. One should define the number of buckets by a power of two -- 2^n, like 2, 4, 8, 16 etc to achieve best results. Again bucketing will help concurrency in Hive. It may even allow a partition wise join i.e. a join between two tables that are bucketed on the same column with the same number of buckets (anyone has tried this?) One more things. When one defines the number of buckets at table creation level in Hive, the number of partitions/files will be fixed. In contrast, with partitioning you do not have this limitation. . Have you considered creating these tables as ORC tables? HTH Dr Mich Talebzadeh LinkedIn https://www.linkedin.com/profile/view?id=AAEAAAAWh2gBxianrbJd6zP6AcPCCdOABUrV8Pw Sybase ASE 15 Gold Medal Award 2008 A Winning Strategy: Running the most Critical Financial Data on ASE 15 http://login.sybase.com/files/Product_Overviews/ASE-Winning-Strategy-091908.pdf Author of the books "A Practitioner’s Guide to Upgrading to Sybase ASE 15", ISBN 978-0-9563693-0-7. co-author "Sybase Transact SQL Guidelines Best Practices", ISBN 978-0-9759693-0-4 Publications due shortly: Complex Event Processing in Heterogeneous Environments, ISBN: 978-0-9563693-3-8 Oracle and Sybase, Concepts and Contrasts, ISBN: 978-0-9563693-1-4, volume one out shortly http://talebzadehmich.wordpress.com <http://talebzadehmich.wordpress.com/> NOTE: The information in this email is proprietary and confidential. This message is for the designated recipient only, if you are not the intended recipient, you should destroy it immediately. Any information in this message shall not be understood as given or endorsed by Peridale Technology Ltd, its subsidiaries or their employees, unless expressly so stated. It is the responsibility of the recipient to ensure that this email is virus free, therefore neither Peridale Technology Ltd, its subsidiaries nor their employees accept any responsibility. From: Akansha Jain [mailto:akansha.15au...@gmail.com <mailto:akansha.15au...@gmail.com> ] Sent: 22 January 2016 23:20 To: user@hive.apache.org <mailto:user@hive.apache.org> Subject: RE: Hive Bucketing Thanks for response. I am using 0.13 mapr version. Could you tell more about bucket pruning. On Jan 22, 2016 3:09 PM, "Mich Talebzadeh" <m...@peridale.co.uk <mailto:m...@peridale.co.uk> > wrote: Ok we are talking about bucket pruning here What version of Hive are using? Bucket pruning I believe is available from version 2.0 HTH Dr Mich Talebzadeh LinkedIn https://www.linkedin.com/profile/view?id=AAEAAAAWh2gBxianrbJd6zP6AcPCCdOABUrV8Pw Sybase ASE 15 Gold Medal Award 2008 A Winning Strategy: Running the most Critical Financial Data on ASE 15 http://login.sybase.com/files/Product_Overviews/ASE-Winning-Strategy-091908.pdf Author of the books "A Practitioner’s Guide to Upgrading to Sybase ASE 15", ISBN 978-0-9563693-0-7. co-author "Sybase Transact SQL Guidelines Best Practices", ISBN 978-0-9759693-0-4 Publications due shortly: Complex Event Processing in Heterogeneous Environments, ISBN: 978-0-9563693-3-8 Oracle and Sybase, Concepts and Contrasts, ISBN: 978-0-9563693-1-4, volume one out shortly http://talebzadehmich.wordpress.com <http://talebzadehmich.wordpress.com/> NOTE: The information in this email is proprietary and confidential. This message is for the designated recipient only, if you are not the intended recipient, you should destroy it immediately. Any information in this message shall not be understood as given or endorsed by Peridale Technology Ltd, its subsidiaries or their employees, unless expressly so stated. It is the responsibility of the recipient to ensure that this email is virus free, therefore neither Peridale Technology Ltd, its subsidiaries nor their employees accept any responsibility. From: Akansha Jain [mailto:akansha.15au...@gmail.com <mailto:akansha.15au...@gmail.com> ] Sent: 22 January 2016 21:55 To: user@hive.apache.org <mailto:user@hive.apache.org> Subject: Hive Bucketing Hi All, I have enabled bucketing in table. I created 256 buckets on user id. Now when I am querying (select count(*) from table where userid =172839393) that table, map reduce should only use single partitioned file as input to mappers. But its considering all files as input to mapper and I don't see any performance benefit when I run same query in unbucketed table. Do I have to set any property before running queries on bucketed tables. I tried join query also, but no performance improvement. In fact, I think it's taking few more seconds as compared to unbucketed table. Thanks, AJ
