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DBD recommendations based on amount of data?
DreaBrandford
Vertica Employee Employee
Is the amount of data in the tables important for the design recommendations made by DBD? In other words, does a large amount of data required for the DBD to make a good recommendation ?
Asked during BDC session Vertica Database Designer – Today and Tomorrow
@ybei
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I think it makes a difference when it comes to recommending a projection that is unsegmented (which is recommended for smaller tables) vs a projection that is segmented. My personal rule of thumb is to default to an unsegmented projection on a table with less than 1 million rows. I am not sure exactly what amount the DBD uses when recommending one vs the other but I do believe itt takes itt into account for this purpose only.
Check out:
dbadmin=> SELECT parameter_name, default_value, description FROM configuration_parameters WHERE parameter_name IN ('DBDRepLargeRowCountPct', 'DBDRepSmallRowCountPct', 'DBDLargestTableRowCountBoundary'); parameter_name | default_value | description ---------------------------------+---------------+------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------ DBDRepLargeRowCountPct | 1.000000 | If the largest fact table has more than <DBDLargestTableRowCountBoundary> rows, then use this percentage off the largest fact table to define the number of rows below which a table should be replicated Default: 1% DBDRepSmallRowCountPct | 10.000000 | If the largest fact table has less than <DBDLargestTableRowCountBoundary> rows, then use this percentage off the largest fact table to define the number of rows below which a table should be replicated Default: 10% DBDLargestTableRowCountBoundary | 1000000 | Number of minimum rows expected in Fact Table, default 1M rows (3 rows)