EXPLAIN REBALANCE PARTITIONS

Warning

SingleStore 9.0 gives you the opportunity to preview, evaluate, and provide feedback on new and upcoming features prior to their general availability. In the interim, SingleStore 8.9 is recommended for production workloads, which can later be upgraded to SingleStore 9.0.

Syntax

SQL

EXPLAIN REBALANCE PARTITIONS ON db_name

Remarks

db_name - name of a SingleStore database.
Node Requirements for SingleStore Commands
See MV_REBALANCE_STATUS for the column definitions in the result set.

The Ordinal is the target partition’s ordinal, and the Target_Host and Target_Port correspond to the destination leaf. Any two operations in the same Phase can be run in parallel and phases are run in order. For example, the aggregator can run COPY PARTITION on partitions test:1 and test:3 in parallel. The exact meaning of what each phase means is arbitrary and depends on the particular rebalance operation. The Estimated_Time_Remaining_Ms is the estimated total time (in milliseconds) that each low-level command will take to complete.

Example

SQL

EXPLAIN REBALANCE PARTITIONS ON memsql_demo;

+-----------------------------+---------+-------------+-------------+-------+-----------------------------+
| Action                      | Ordinal | Target_Host | Target_Port | Phase | Estimated_Time_Remaining_Ms |
+-----------------------------+---------+-------------+-------------+-------+-----------------------------+
| COPY PARTITION              | 13      | 127.0.0.1   | 10002       | 3     | 7821                        |
| COPY PARTITION              | 2       | 127.0.0.1   | 10003       | 4     | 7821                        |
| COPY PARTITION              | 2       | 127.0.0.1   | 10004       | 4     | 7821                        |
| PROMOTE PARTITION WITH DROP | 2       | 127.0.0.1   | 10003       | 5     | 1351                        |
| DROP PARTITION              | 2       | 127.0.0.1   | 10002       | 6     | 1002                        |
| DROP PARTITION              | 13      | 127.0.0.1   | 10004       | 6     | 1002                        |
+-----------------------------+---------+-------------+-------------+-------+-----------------------------+

Note: The Estimated_Time_Remaining_Ms is the estimated total time (in milliseconds) that each low-level command will take to complete.

Understanding the Rebalance Actions

Each action occurs on a single partition.

Action	Definition
`COPY PARTITION`	Copies a partition and sets up replication to keep the copy in sync.
`PROMOTE PARTITION [WITH {DROP,REPOINT}]`	Promotes a replica partition into a master partition. The `WITH DROP` clause drops the previous master partition. The `WITH REPOINT` clause converts the previous master partition into a replica partition. There is no default, rebalance chooses one or the other based on the path to get to a balanced set of partitions.
`DROP PARTITION`	Drops a partition.