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What's new in Apache Hive
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What's new in Apache Hive

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  • 1. HiveWhat’s new and what’s next?Gunther HagleitnerHortonworks@yakrobat Page 1
  • 2. STINGER Initiative SPEEED!! POWERRR!! – Jeremy Clarkson Page 2
  • 3. ROLLUP, CUBE (Hive 0.10)select state, year, sum(amt_paid) select state, year, sum(amt_paid)from sales from salesgroup by state, year with rollup group by state, year with cubeState Year Sum State Year SumCA 2011 20000 CA 2011 20000CA 2012 25000 CA 2012 25000CA * 45000 CA * 45000NY 2012 15000 NY 2012 15000NY * 15000 NY * 15000* * 60000 * * 60000 * 2011 20000 * 2012 40000 HIVE-3433 Page 3
  • 4. Support for Analytics• Simple analytical tasks can turn into unintuitive and inefficient queriesselect count(*) as rk, s2.state as state, s2.product as product, avg(s2.amt_paid), sum(s1.amt_paid)from sales s1 join sales s2 on (s1.product = s2.product and s1.state = s2.state)where s1.year <= s2.yeargroup by s2.state, s2.product, s2.yearorder by state, product, rk; Page 4
  • 5. Support for Analytics• Simple numbering + running total Number State Product Amount Total 1 CA A 1000 1000 2 CA A 500 1500 3 CA A 700 2200 4 CA A 300 2500 1 CA B 500 500 2 CA B 500 1000 Page 5
  • 6. Support for Analytics• Faster, but still not very intuitiveselect state, product, amt_paid, rsum(hash(state, product),amt_paid)from( select state, product, amt_paid from sales distribute by hash(state,product) sort by state, product) t; Page 6
  • 7. Support for Analytics – OVER clause• Now that’s more like itselect rank() over state_and_product, state, product, amt_paid, sum(amt_paid) over state_and_productfrom saleswindow state_and_product as (partition by state, product order by year); Page 7
  • 8. Support for Analytics – OVER clause partition by order by rows AL 2012 1000.00 CA 2010 2000.00 CA 2011 2000.00 CA 2012 4000.00 CA 2013 1000.00 NY 2012 500.00• OVER clause – PARTITION BY, ORDER BY, ROWS BETWEEN/FOLLOWING/PRECEDING – Works with current aggregate functions – New aggregates/window functions – RANK, LEAD, ROW_NUMBER, LAG, LEAD, FIRST_VALUE, LAST_VALUE – NTILE, DENSE_RANK, CUME_DIST, PERCENT_RANK, PERCENT_CONT, PERCENT_DISC HIVE-896 Page 8
  • 9. Support for Analytics Continued• Sub-queries in WHERE – Non-correlated only – [NOT] IN supported – Plan to optimize to fit in memory as hash table when feasible, join when not• Standard SQL data types – datetime – char() and varchar() – add precision and scale to decimal and float – aliases for standard SQL types (BLOB = binary, CLOB = string, integer = int, real/number = decimal) Page 9
  • 10. Automatic join conversion Sorted? Sorted? Sort Merge Sort Merge Bucket Join Bucket Join • When enabled hive will automatically pick join implementation • Query hints no longer needed • Can be configured to run without conditional tasks HIVE-3784 Page 10
  • 11. Merging join tasksselect Task Task Task … Mapjoin Mapjoin Mapjoin Mapjoin Mapjoin Mapjoinfrom sales join date_dim on (…) join time_dim on (…) join state on (…) Task … Mapjoin -> Mapjoin ->Mapjoin Mapjoin -> Mapjoin ->Mapjoin•Used to generate sequence of map-only jobs•Hive will now do as many map-joins as fit in memory in single map-only job•Memory limit is configurable•Memory size is estimated from file size HIVE-3784 Page 11
  • 12. M-MR to MRselect Map Task Map Task Reduce Task sum(…) Mapjoin Mapside Group Mapjoin Mapside Group … Aggr Aggr by/Aggr by/Aggrfrom sales join date_dim on (…)group by … Map Task Reduce Task … Mapjoin -> Mapside Mapjoin -> Mapside Group by/Aggr Group by/Aggr Aggr Aggr•Used to run as map-only job followed by a map-reduce job•Hive will now merge the two map tasks HIVE-3952 Page 12
  • 13. Group by/Order by (ReduceSinkDeDup)select Map Task Reduce Task Map Task Reduce Task … Map- Group Noop Noop Map- Group Noop Noopfrom sales side/Aggr side/Aggr by/Aggr by/Aggrgroup by store, itemorder by store Map Task Reduce Task Map- Map- Group Group side/Aggr side/Aggr by/Aggr by/Aggr•Used to generate map-reduce job for group by followed by map-reduce job fororder by•Hive will now do both in same job•More general: Will search for reduce sinks on same keys and combine•Caution: Might degrade performance if difference in num reducers is big HIVE-2340 Page 13
  • 14. Upcoming: Limit pushdownselect Map Task Reduce Task … Map- Group Map- Groupfrom sales side/Aggr side/Aggr by/Aggr+Limit by/Aggr+Limit group by store, item order by storelimit 20 Map Task Reduce Task Map-side/Aggr Map-side/Aggr Group Group +Top-k +Top-k by/Aggr+Limit by/Aggr+Limit•Used to output all pre-aggregated data from map task and limit the output inthe reducer•Hive will keep a top-k list of elements in each map task, reducing the amountof data to be shuffled HIVE-3562 Page 14
  • 15. Upcoming: Total order sort• Order by queries no longer result in single reducer• Makes it easier to apply optimizations such as group by/order by• Requires knowledge of the key distribution (sampling) HIVE-1402 Page 15
  • 16. ORC – Optimized RCFile HIVE-3874 Page 16 © Hortonworks Inc. 2012
  • 17. File Layout Page 17 © Hortonworks Inc. 2012
  • 18. ORC-enabled improvements Page 18 © Hortonworks Inc. 2012
  • 19. Beyond Batch with YARN & Tez Tez Generalizes Map-Reduce Always-On Tez ServiceSimplified execution plans process Low latency processing for data more efficiently all Hadoop data processing Page 19
  • 20. Tez Service• Hive Query Startup Expensive – Job launch & task-launch latencies are fatal for short queries (in order of 5s to 30s)• Solution – Tez Service – Removes task-launch overhead – Removes job-launch overhead – Hive – Submit query-plan to Tez Service – Native Hadoop service, not ad-hoc Page 20
  • 21. Tez- Core IdeaTask with pluggable Input, Processor & Output Input Input Processor Processor Output Output Tez Task YARN ApplicationMaster to run DAG of Tez Tasks Page 21
  • 22. Hive/MR versus Hive/Tez select a.state, count(*) from a join b on (a.id = b.id) group by a.state I/O Synchronization I/O Pipelining Barrier Hive - MR Hive - Tez Page 22
  • 23. Hive/MR versus Hive/Tez select store, state, total from (select storeid, sum(sales_price) total from sales s join date_dim d on (s.dateid = d.dateid) where d.year = 2012 group by storeid ) ss join (select storeid, store, state from store join state on (store.stateid = state.stateid) ) sd on (sd.storeid = ss.storeid) Hive - MR Hive - Tez Page 23
  • 24. Hive Performance Longer Term - Caching• Need to be able to keep hot data sets in memory• Could be done via pinning files in OS buffer cache• Could be done with separate process running its own buffer cache• Need to evaluate best plan• Would like to pin dimension tables in memory• Latest partitions of large tables also a candidate• Ideally will include changes to the scheduler to understand which nodes have which partitions/tables cached Page 24
  • 25. Hive Performance Longer Term -Vectorization• Rewrite operators to work on arrays of Java scalars• MonetDB paper• Operates on blocks of 1K or more records• Each block contains an array of Java scalars, one for each column• Avoids many function calls• Size to fit in L1 cache, avoid cache misses• Generate code for operators on the fly to avoid branches in code, maximize deep pipelines of modern processers• Requires conversion of all column values to Java scalars – no objects allowed – Integrates nicely with ORC work, other input types will need conversion on reading• Want to write this in a way it can be shared by Pig, Cascading, MR programmers Page 25
  • 26. Page 26