EXPLAIN REBALANCE PARTITIONS
Returns the set of steps that REBALANCE PARTITIONS would run if you executed it now.
Syntax
EXPLAIN REBALANCE PARTITIONS ON db_name
Remarks
db_name
- name of a SingleStoreDB database.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
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 |
---|---|
| Copies a partition and sets up replication to keep the copy in sync. |
| Promotes a replica partition into a master partition. The |
| Drops a partition. |