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      CoursesIT & SoftwareDatabasesGreenplum Database
      • Greenplum Tutorial
        9
        • Lecture1.1
          Download the Greenplum Sandbox VM 30 min
        • Lecture1.2
          Greenplum Database Architecture 30 min
        • Lecture1.3
          Greenplum Configuration Files ( pg_hba.conf , postgresql.conf ) 30 min
        • Lecture1.4
          Greenplum Database Installation 30 min
        • Lecture1.5
          Greenplum psql Command Line Client 30 min
        • Lecture1.6
          Greenplum Create Users and Roles 30 min
        • Lecture1.7
          Greenplum Create and Prepare Database 30 min
        • Lecture1.8
          Greenplum Create Tables 30 min
        • Lecture1.9
          Greenplum Data Loading 30 min
      • Greenplum Performance Tuning
        7
        • Lecture2.1
          Greenplum Performance Tuning Overview 30 min
        • Lecture2.2
          Greenplum Analyze the tables 30 min
        • Lecture2.3
          Greenplum explain plans 30 min
        • Lecture2.4
          Greenplum Indexes and performance 30 min
        • Lecture2.5
          Greenplum Row vs. column orientation 30 min
        • Lecture2.6
          Greenplum – Check for even data distribution on segments 30 min
        • Lecture2.7
          Greenplum Partitioning 30 min
      • Greenplum Database Analytics
        1
        • Lecture3.1
          Greenplum Database analytics 30 min
      • Greenplum Backup and Recovery Operations
        2
        • Lecture4.1
          Greenplum gpcrondump 30 min
        • Lecture4.2
          Greenplum gpdbrestore 30 min
      • Importing GPDB Sandbox
        1
        • Lecture5.1
          Importing GPDB Sandbox into VMware Fusion 30 min
      • Greenplum Database Books
        1
        • Lecture6.1
          Data Warehousing with Greenplum PDF 30 min
      • Basic Questions and Answer of Greenplum Database
        1
        • Lecture7.1
          Some basic Questions and answer about Greenplum database 30 min

        Greenplum – Check for even data distribution on segments

        Check for even data distribution on segments

        The faa.otp_r and faa.otp_c tables are distributed with a hash function on UniqueCarrier and FlightNum. These two columns were selected because they produce an even distribution of the data onto the segments. Also, with frequent joins expected on the fact table and dimension tables on these two columns, less data moves between segments, reducing query execution time. When there is no advantage to co-locating data from different tables on the segments, a distribution based on a unique column ensures even distribution. Distributing on a column with low cardinality, such as Diverted, which has only two values, will yield a poor distribution.

        1. One of the goals of distribution is to ensure that there is approximately the same amount of data in each segment. The query below shows one way of determining this. Since the column-oriented and row-oriented tables are distributed by the same columns, the counts should be the same for each.
          tutorial=# SELECT gp_segment_id, COUNT(*) FROM faa.otp_c GROUP BY
          gp_segment_id ORDER BY gp_segment_id;
          gp_segment_id |  count
          ---------------+---------
                   0 | 1028144
                   1 | 1020960
          (2 rows)

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