Venki Korukanti created DRILL-4446:
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Summary: Improve current fragment parallelization module
Key: DRILL-4446
URL: https://issues.apache.org/jira/browse/DRILL-4446
Project: Apache Drill
Issue Type: New Feature
Affects Versions: 1.5.0
Reporter: Venki Korukanti
Assignee: Venki Korukanti
Fix For: 1.6.0
Current fragment parallelizer {{SimpleParallelizer.java}} can’t handle
correctly the case where an operator has mandatory scheduling requirement for a
set of DrillbitEndpoints and affinity for each DrillbitEndpoint (i.e how much
portion of the total tasks to be scheduled on each DrillbitEndpoint). It
assumes that scheduling requirements are soft (except one case where Mux and
DeMux case where mandatory parallelization requirement of 1 unit).
An example is:
Cluster has 3 nodes running Drillbits and storage service on each. Data for a
table is only present at storage services in two nodes. So a GroupScan needs to
be scheduled on these two nodes in order to read the data. Storage service
doesn't support (or costly) reading data from remote node.
Inserting the mandatory scheduling requirements within existing
SimpleParallelizer is not sufficient as you may end up with a plan that has a
fragment with two GroupScans each having its own hard parallelization
requirements.
Proposal is:
Add a property to each operator which tells what parallelization implementation
to use. Most operators don't have any particular strategy (such as Project or
Filter), they depend on incoming operator. Current existing operators which
have requirements (all existing GroupScans) default to current parallelizer
{{SimpleParallelizer}}. {{Screen}} defaults to new mandatory assignment
parallelizer. It is possible that PhysicalPlan generated can have a fragment
with operators having different parallelization strategies. In that case an
exchange is inserted in between operators where a change in parallelization
strategy is required.
Will send a detailed design doc.
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