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https://issues.apache.org/jira/browse/IMPALA-3807?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Dimitris Tsirogiannis resolved IMPALA-3807.
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Resolution: Fixed
Fix Version/s: Impala 2.9.0
> Introduce support for dedicated Impalad coordinator(s)
> ------------------------------------------------------
>
> Key: IMPALA-3807
> URL: https://issues.apache.org/jira/browse/IMPALA-3807
> Project: IMPALA
> Issue Type: New Feature
> Components: Backend
> Affects Versions: Impala 2.8.0
> Reporter: Mostafa Mokhtar
> Labels: performance, scalability
> Fix For: Impala 2.9.0
>
>
> After running large scale concurrent tests it was obvious that a dedicated
> coordinator.
> During the concurrency tests resource utilization in terms of CPU, Memory and
> Network were significantly higher than other worker nodes.
> The increase in resource utilization was mostly due to
> * Sending exec plan fragment to remote fragments, ExecPlanFragment can become
> very large for complex queries with lots of files & partitions
> * Runtime filters consume lots of untracked memory when the bloom filters are
> aggregated
> * Runtime filters consume lots of Network throughput on the coordinator as it
> receives, aggregates and sends the filters
> * Aggregating RunProfile counters
> * When CPU utilization on the coordinator is high remote fragments
> occasionally fail with "Couldn't get a client for
> impala-8-2.vpc.cloudera.com:22000 Reason: Couldn't open transport for
> impala-compete-8-2.vpc.cloudera.com:22000 (connect() failed: Connection timed
> out)"
> * Slow start of remote query fragments specially when the coordinator node is
> under heavy load
> * Admission control counters can become out of sync when using multiple
> coordinators
> Metadata should naturally benefit from running a dedicated coordinator as
> metadata is less likely to become out of sync and one day we can get rid of
> expensive catalog updates.
> The dedicated coordinator should only run the +Coordinator Fragment+ and not
> participate in any scans, aggs etc..
> This work will require CM support.
> Running a dedicated coordinator significantly improved performance of
> complex TPC-DS queries
> |Query||Baseline (seconds)||Dedicated coord (seconds)||Speedup %|
> |74|73|43|70%|
> |75|152|91|67%|
> |4|127|78|63%|
> |25|53|34|56%|
> |95|35|23|52%|
> |11|82|54|52%|
> |85|37|25|48%|
> |17|71|48|48%|
> |64|147|101|46%|
> |29|65|47|38%|
> |72|408|312|31%|
> |18|36|28|29%|
> |44|36|28|29%|
> |60|6|5|20%|
> |77|12|10|20%|
> |50|43|36|19%|
> |5|60|51|18%|
> |81|14|12|17%|
> |23|198|170|16%|
> |80|29|25|16%|
> |35|22|19|16%|
> |68|15|13|15%|
> |78|551|486|13%|
> |31|36|32|13%|
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