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The new Summary Collect Statistics feature starting with Teradata Release 14

 

Summary statistics are a very useful feature, which is new in Teradata Release 14. Contrary to traditional statistics, which are collected on columns or indexes, summary statistics are table level statistics:

COLLECT SUMMARY STATISTICS ON <TABLE>;

Table level statistics are the information about the number of rows per table, the average data block sizes, and the average row sizes.

The number of rows per table is a critical measure for the Teradata Optimizer to estimate the cost of a full table scan. So, how was this information made available in previous releases of Teradata?

In earlier versions of Teradata, this was achieved by collecting column statistics on the dummy “PARTITION” and the Primary Index columns.

Summary statistics which are defined on a table will be refreshed each time the statistics on any column of the table are updated. If you want to avoid the waste of resources, the best practice is to update all column statistics at once instead of doing it column by column:

The excellent solution is this one:

COLLECT STATISTICS ON <TABLE>; — all column statistics are refreshed, summary statistics are only updated once.

Although less intense on resources than traditional column/index statistics, this should still be avoided:

COLLECT STATISTICS ON <TABLE> <COLUMN_1>; — first collection of summary statistics

COLLECT STATISTICS ON <TABLE> <COLUMN_2>; — needless 2nd collection of summary statistics

Conclusion: Summary statistics collection is a very useful feature to refresh the number of rows information per table quickly.

Roland Wenzlofsky
 

Roland Wenzlofsky is a graduated computer scientist and Data Warehouse professional working with the Teradata database system for more than 15 years. He is experienced in the fields of banking and telecommunication with a strong focus on performance optimization.

  • Avatar Dimitrios says:

    Hello,

    This new feature has only advantages , except from one thing , the way that we have to change the procedure which collect the stats in order to use this feature(s) (plus the max value length / max internal and sample ).

    It is also recommended to big tables , where collecting stats consumes a lot of io/cpu , just
    Collect Summary Stats on DB.TB ; ,after every DML transaction on it , in order to have updated summary stats on the table , in this way we help the parser to make better extrapolations .

  • Avatar Johne490 says:

    Very informative post.Really thank you! Awesome.

  • Avatar Sreeraj says:

    Thank you. very informative.
    Question: for TD 14 onwards, the best practice is to collect all column statistics at once instead of column by column. is this true for big tables as well? I was under the impression that we need to collect stats only for certain columns based on the PI / join and WHERE. could you please clarifiy?

  • Roland Wenzlofsky Roland Wenzlofsky says:

    Hi Sreeraj. I think this is a misunderstanding.

    “All columns at once” means to collect statistics with the new syntax which allows to collect the stats on different columns of the same table at once.

    Before Teradata 14 we had to collect stats column by column i.e. issue one statement per column. The only performance advantage previously possible was synchronized scanning on the spool (this was achieved by starting the collect statistics statements for one table at the same time).

    “All columns at once” does not mean to collect statistics on each and every column of a table…

    Roland

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