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https://issues.apache.org/jira/browse/HIVE-23006?focusedWorklogId=415293&page=com.atlassian.jira.plugin.system.issuetabpanels:worklog-tabpanel#worklog-415293
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ASF GitHub Bot logged work on HIVE-23006:
-----------------------------------------
Author: ASF GitHub Bot
Created on: 03/Apr/20 02:53
Start Date: 03/Apr/20 02:53
Worklog Time Spent: 10m
Work Description: jcamachor commented on issue #952: HIVE-23006
ProbeDecode compiler support
URL: https://github.com/apache/hive/pull/952#issuecomment-608201286
@pgaref , thanks for changes. Patch looks good. About the name, I think it
is fine (probe side for the filtering generated statically in case of
expressions or dynamically for joins).
I think main remaining issue is related to selection in case of multiple MJ
operators. I was thinking that for the time being, we could make the policy
pluggable via config and have three very simple ones: 1) keep all of them, 2)
keep the one with lowest `ndv_JOIN_key_column / ndv_TS_target_column` ratio, or
3) keep those with ratio below a certain threshold specified through a config
value. Alternatively, in this patch you could maybe go only with option 2 and
tackle others in follow-up.
You have the information about the stats in the operators themselves (follow
`op.getStatistics()` calls to see how it is retrieved per column basis). Thus,
I would make that decision in the TezCompiler (once we gather all the context
information) rather than GenTezUtils.
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Issue Time Tracking
-------------------
Worklog Id: (was: 415293)
Time Spent: 40m (was: 0.5h)
> Compiler support for Probe MapJoin
> ----------------------------------
>
> Key: HIVE-23006
> URL: https://issues.apache.org/jira/browse/HIVE-23006
> Project: Hive
> Issue Type: Sub-task
> Reporter: Panagiotis Garefalakis
> Assignee: Panagiotis Garefalakis
> Priority: Major
> Labels: pull-request-available
> Time Spent: 40m
> Remaining Estimate: 0h
>
> The decision of pushing down information to the Record reader (potentially
> reducing decoding time by row-level filtering) should be done at query
> compilation time.
> This patch adds an extra optimisation step with the goal of finding Table
> Scan operators that could reduce the number of rows decoded at runtime using
> extra available information.
> It currently looks for all the available MapJoin operators that could use the
> smaller HashTable on the probing side (where TS is) to filter-out rows that
> would never match.
> To do so the HashTable information is pushed down to the TS properties and
> then propagated as part of MapWork.
> If the a single TS is used by multiple operators (shared-word), this rule can
> not be applied.
> This rule can be extended to support static filter expressions like:
> _select * from sales where sold_state = 'PR';_
> This optimisation manly targets the Tez execution engine running on Llap.
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