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From "ASF GitHub Bot (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (PHOENIX-3744) Support snapshot scanners for MR-based queries
Date Wed, 24 May 2017 17:23:04 GMT

    [ https://issues.apache.org/jira/browse/PHOENIX-3744?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16023273#comment-16023273
] 

ASF GitHub Bot commented on PHOENIX-3744:
-----------------------------------------

Github user JamesRTaylor commented on a diff in the pull request:

    https://github.com/apache/phoenix/pull/239#discussion_r118313746
  
    --- Diff: phoenix-core/src/main/java/org/apache/phoenix/mapreduce/PhoenixInputFormat.java
---
    @@ -185,7 +184,7 @@ private QueryPlan getQueryPlan(final JobContext context, final Configuration
con
                     scan.setAttribute(BaseScannerRegionObserver.TX_SCN, Bytes.toBytes(Long.valueOf(txnScnValue)));
                 }
                 // Initialize the query plan so it sets up the parallel scans
    -            queryPlan.iterator(MapReduceParallelScanGrouper.getInstance());
    +            queryPlan.iterator(TableMRParallelScanGrouper.init(configuration));
    --- End diff --
    
    Can't this just instantiate a TableMRParallelScanGrouper and the init method can be invoked
in the constructor so that it doesn't need to be exposed in the interface?


> Support snapshot scanners for MR-based queries
> ----------------------------------------------
>
>                 Key: PHOENIX-3744
>                 URL: https://issues.apache.org/jira/browse/PHOENIX-3744
>             Project: Phoenix
>          Issue Type: Bug
>            Reporter: James Taylor
>            Assignee: Akshita Malhotra
>         Attachments: PHOENIX-3744.patch
>
>
> HBase support scanning over snapshots, with a SnapshotScanner that accesses the region
directly in HDFS. We should make sure that Phoenix can support that.
> Not sure how we'd want to decide when to run a query over a snapshot. Some ideas:
> - if there's an SCN set (i.e. the query is running at a point in time in the past)
> - if the memstore is empty
> - if the query is being run at a timestamp earlier than any memstore data
> - as a config option on the table
> - as a query hint
> - based on some kind of optimizer rule (i.e. based on estimated # of bytes that will
be scanned)
> Phoenix typically runs a query at the timestamp at which it was compiled. Any data committed
after this time should not be seen while a query is running.



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