terrymanu commented on issue #37179:
URL:
https://github.com/apache/shardingsphere/issues/37179#issuecomment-3582402839
## Problem Understanding
The asks split into two: (1) change shard count with automatic data
redistribution; (2) have ShardingSphere sense DB high availability and auto
switch / service discovery.
## Problem Root Cause
ShardingSphere is positioned as a database traffic management layer with
fixed sharding-key mapping. It does not manage data redistribution, nor does it
manage or sense database HA status. This is a scoped design choice, not a
defect.
## Problem Analysis
- Automatic data redistribution: The community edition does not provide
automatic re-sharding/rebalancing. Changing shard count requires an explicit
migration/scale process (see official Data Pipeline docs:
https://shardingsphere.apache.org/document/current/en/features/
data-migration/).
- Database HA discovery: ShardingSphere does not handle instance health or
failover; that’s handled by the database’s own HA (e.g., MySQL
GR/primary-standby) or external components. ShardingSphere focuses on
rule-driven routing/traffic governance and keeps HA detection
and write drift out of scope for lightness.
- If you need both automatic redistribution and HA sensing together,
consider SphereEx DBPlusEngine (built on ShardingSphere) which claims to
implement both. Website: https://www.sphere-ex.com/.
## Problem Conclusion
This is an out-of-scope feature request, not a known bug. ShardingSphere
keeps fixed sharding mapping and a lightweight scope, so it will not add
automatic data redistribution or built-in DB HA detection/switching. If you
need these:
1. Use the database’s HA for failover;
2. Use external data migration for shard changes;
3. Or evaluate SphereEx DBPlusEngine for integrated support.
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