[IMPALA-8341] Data cache for remote reads - ASF JIRA

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Details

Type: Improvement
Status: Resolved
Priority: Critical
Resolution: Fixed
Affects Version/s: Impala 3.2.0
Fix Version/s: Impala 3.3.0
Component/s: Backend
Labels:
None

Epic Color:
ghx-label-4

Description

When running in public cloud (e.g. AWS with S3) or in certain private cloud settings (e.g. data stored in object store), the computation and storage are no longer co-located. This breaks the typical pattern in which Impala query fragment instances are scheduled at where the data is located. In this setting, the network bandwidth requirement of both the nics and the top of rack switches will go up quite a lot as the network traffic includes the data fetch in addition to the shuffling exchange traffic of intermediate results.

To mitigate the pressure on the network, one can build a storage backed cache at the compute nodes to cache the working set. With deterministic scan range scheduling, each compute node should hold non-overlapping partitions of the data set.

An initial prototype of the cache was posted here: https://gerrit.cloudera.org/#/c/12683/ but it probably can benefit from a better eviction algorithm (e.g. LRU instead of FIFO) and better locking (e.g. not holding the lock while doing IO).