ColumnStore Redistribute Data

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Redistribute Data command is available from the MariaDB ColumnStore Admin console. Its called "redistributeData"

It is used to balance Partitions among the dbroots. This command has three possible options: START, STOP and STATUS.

The redistribute command acts at Partition granularity, which means that a minimal move is 64000000 rows. Any table smaller than that will not be redistributed and there may be as much as one full Partition difference in the resulting balance.

Redistribute can take a long time. During this time, we recommend that all data manipulation including bulk inserts are suspended.

Deleted records still take up space, so deleting a bunch of rows won't affect Redistribute. Even TRUNCATE doesn't really get rid of the partition, though the space may eventually get re-used. DROP PARTITION will affect the balancing of Redistribute.

If Redistribute STOP is called, all processing stops where it's at, but in a usable state. Redistribute STATUS can be used to see how much has been done. A further Redistribute START will start over using the new state of the system. This may lead to a less optimal distribution, so STOP-START sequences aren't recommended.

While the system is working, Redistribute STATUS can be called to see what's happening. a -r <count> option can be used on the STATUS command line to repeat the call and act as a monitor.

There is an option on the START command to remove dbroots from the data redistribution. The result will be that all data is distributed to the remaining dbroots and the removed dbroots will have no data. This can be used prior to the physical removal of dbroots from the system.

Redistribute START REMOVE <dbroot list>

To see how much data resides on any given dbroot for a table, you can use a query like: select count(*) from <table> where idbdbroot(<any column>)=<dbrootnum>;


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