Important

Self-managed SingleStore will soon transition from version 9.1 RC to version 10. This new semantic versioning scheme will provide SingleStore with finer control over engine and feature releases that were not possible with the current versioning scheme.

In the interim, SingleStore 9.1 RC can be used to preview, evaluate, and provide feedback on the new and upcoming features in SingleStore 10 prior to its general availability. Ahead of this transition, SingleStore 9.0 is recommended for production workloads, which can later be upgraded to SingleStore 10.

EXPLAIN REBALANCE PARTITIONS

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.