TR-09-4.pdf

"MCC-DB: minimizing cache conflicts in muli-core processors for databases"

Rubao Lee, Xiaoning Ding, Feng Chen, Qingda Lu, and  Xiaodong Zhang 

Proceedings of 35th International Conference on Very Large Data Bases, 
(VLDB 2009), Lyon, France, August 24-28, 2009. 


Abstract

In a typical commercial multi-core processor, the last level
cache (LLC) is shared by two or more cores. Existing studies
have shown that the shared LLC is beneficial to concurrent
query processes with commonly shared data sets. However,
the shared LLC can also be a performance bottleneck to concurrent
queries, each of which has private data structures,
such as a hash table for the widely used hash join operator,
causing serious cache conflicts. We show that cache conflicts
on multi-core processors can significantly degrade overall
database performance. In this paper, we propose a hybrid
system method called MCC-DB for accelerating executions of
warehouse-style queries, which relies on the DBMS knowledge
of data access patterns to minimize LLC conflicts in multicore
systems through an enhanced OS facility of cache partitioning.
MCC-DB consists of three components: (1) a cacheaware
query optimizer carefully selects query plans in order to
balance the numbers of cache-sensitive and cache-insensitive
plans; (2) a query execution scheduler makes decisions to corun
queries with an objective of minimizing LLC conflicts;
and (3) an enhanced OS kernel facility partitions the shared
LLC according to each query¢s cache capacity need and locality
strength. We have implemented MCC-DB by patching
the three components in PostgreSQL and Linux kernel. Our
intensive measurements on an Intel multi-core system with
warehouse-style queries show that MCC-DB can reduce query
execution times by up to 33%.

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