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Date: Thu, 1 Jun 2017 23:20:05 +0000 (UTC)
From: "Vineet Garg (JIRA)" <jira@apache.org>
To: issues@hive.apache.org
Message-ID: <JIRA.13076682.1496359192000.346769.1496359205438@Atlassian.JIRA>
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Subject: [jira] [Assigned] (HIVE-16811) Estimate statistics in absence of
 stats
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archived-at: Thu, 01 Jun 2017 23:20:11 -0000


     [ https://issues.apache.org/jira/browse/HIVE-16811?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]

Vineet Garg reassigned HIVE-16811:
----------------------------------


> Estimate statistics in absence of stats
> ---------------------------------------
>
>                 Key: HIVE-16811
>                 URL: https://issues.apache.org/jira/browse/HIVE-16811
>             Project: Hive
>          Issue Type: Improvement
>            Reporter: Vineet Garg
>            Assignee: Vineet Garg
>
> Currently Join ordering completely bails out in absence of statistics and this could lead to bad joins such as cross joins.
> e.g. following select query will produce cross join.
> {code:sql}
> create table supplier (S_SUPPKEY INT, S_NAME STRING, S_ADDRESS STRING, S_NATIONKEY INT, 
> S_PHONE STRING, S_ACCTBAL DOUBLE, S_COMMENT STRING)
> CREATE TABLE lineitem (L_ORDERKEY      INT,
>                                 L_PARTKEY       INT,
>                                 L_SUPPKEY       INT,
>                                 L_LINENUMBER    INT,
>                                 L_QUANTITY      DOUBLE,
>                                 L_EXTENDEDPRICE DOUBLE,
>                                 L_DISCOUNT      DOUBLE,
>                                 L_TAX           DOUBLE,
>                                 L_RETURNFLAG    STRING,
>                                 L_LINESTATUS    STRING,
>                                 l_shipdate      STRING,
>                                 L_COMMITDATE    STRING,
>                                 L_RECEIPTDATE   STRING,
>                                 L_SHIPINSTRUCT  STRING,
>                                 L_SHIPMODE      STRING,
>                                 L_COMMENT       STRING) partitioned by (dl int)
> ROW FORMAT DELIMITED
> FIELDS TERMINATED BY '|';
> CREATE TABLE part(
>     p_partkey INT,
>     p_name STRING,
>     p_mfgr STRING,
>     p_brand STRING,
>     p_type STRING,
>     p_size INT,
>     p_container STRING,
>     p_retailprice DOUBLE,
>     p_comment STRING
> );
> explain select count(1) from part,supplier,lineitem where p_partkey = l_partkey and s_suppkey = l_suppkey;
> {code}
> Estimating stats will prevent join ordering algorithm to bail out and come up with join at least better than cross join 


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