Manikandan R created IMPALA-6856:
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             Summary: High memory estimates in Impala 2.11
                 Key: IMPALA-6856
                 URL: https://issues.apache.org/jira/browse/IMPALA-6856
             Project: IMPALA
          Issue Type: Bug
    Affects Versions: Impala 2.11.0
            Reporter: Manikandan R
         Attachments: query_high_mem_post_upgrade.sql

Upgraded Impala cluster recently from 2.5 to 2.11 through CDH and observed that 
for some queries, memory estimates are very high now compared to pre upgrade 
days. Attached 1 such query whose memory estimates used to be 13-15 GB before 
started showing as 256 GB after the upgrade and not even entering the pool as 
it is directly getting rejected because of max pool size. As a temp fix, We 
have set mem limit for those queries and managing it for now.

In addition, also seeing different memory estimates for different users 
belonging to different pools for the same query. Does pool max size plays an 
any role in memory estimates? Surprisingly, observed this behaviour on 1st day 
of upgrade. Tried to reproduce now,  but it is showing same memory estimates 
for different users.



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