[HIVE-5170] Sorted Bucketed Partitioned Insert hard-codes the reducer count == bucket count

• Type: Bug
• Status: Resolved
• Priority: Major
• Resolution: Done
• Affects Version/s: 0.12.0
• Component/s: Query Processor

Environment

Ubuntu LXC

• Assignee: Unassigned
• Reporter: Gopal Vijayaraghavan
• Created: 29/Aug/13 20:36
• Updated: 14/Oct/14 19:32
• Resolved: 14/Oct/14 19:32

Description

When performing a hive sorted-partitioned insert, the insert optimizer hard-codes the number of output files to the actual bucket count of the table.

https://github.com/apache/hive/blob/trunk/ql/src/java/org/apache/hadoop/hive/ql/parse/SemanticAnalyzer.java#L4852

We need at least that many reducers or if limited, switch to multi-spray (as implemented already), but more reducers is wasteful as long as the HiveKey only contains the partition columns.

At this point, we're limited to reducers = n-bucket still, which is a problem for partitioning requests which need to insert nearly a terabyte of data into a single-digit bucket count and four-digit partition count.

Since that is routed by the hasCode of the HiveKey, we can ensure that works by modifying the HiveKey to handle n-buckets internally.

Basically it should only generate hashCode = (sort_cols.hashCode() % n) routing only to n reducers over-all, despite how many we spin up.

So far so good with the hard-coded reducer count.

But provided we fix the issues brought up by HIVE-5169, the insert becomes friendlier to a higher reducer count as well.

At this juncture, we can modify the hashCode to be slightly more interesting.

hashCode = (part_cols.hashCode()*31 + (sort_cols.hashCode() % n))

This generates somewhere between n to partition_count * n unique hash-codes.

Since the sort-order & bucketing has to be maintained per-partition dir, distributing this equally across any number of reducers will result in the scale-out of the reducer count.

This will allow a reducer count that will allow for far faster inserts of ORC data into a partitioned/sorted table.

Issue Links

• is superceded by: HIVE-6455 Scalable dynamic partitioning and bucketing optimization