terrymanu commented on issue #32150:
URL:
https://github.com/apache/shardingsphere/issues/32150#issuecomment-3638214178
## Understanding:
Using Proxy 5.5.0 (Standalone + JDBC/H2 repository). First start with
default MySQL client on port 3307, register PostgreSQL storage units. After
restart, MySQL client connection hangs; clearing the config repository restores
connectivity. Setting proxy-
frontend-database-protocol-type: MySQL makes it connect, but requires
deleting existing repository. Forcing MySQL frontend then hits SHOW COLUMNS
FROM syntax errors on PostgreSQL backend.
## Root Cause:
Without an explicit frontend protocol, FrontDatabaseProtocolTypeFactory
switches to the storage unit’s database type once metadata is loaded. After
registering PostgreSQL storage, the frontend protocol becomes PostgreSQL on
restart; a MySQL client handshake
is incompatible and appears as a hang. Clearing the repository removes
metadata, so it falls back to default MySQL. Forcing MySQL against a PostgreSQL
backend triggers MySQL-style metadata queries (e.g., SHOW COLUMNS), which fail
on PostgreSQL.
## Analysis:
Current config lacks proxy-frontend-database-protocol-type, and after the
repository is created, Proxy reads from the repository, not the local
global.yaml, so changing the local file alone has no effect. Protocol mismatch
between client/frontend/backend
yields handshake hangs and SQL dialect errors—expected behavior, not a
Proxy defect. Proper usage requires aligning frontend protocol with the client
and backend dialect.
## Conclusion / Guidance:
This is a configuration/usage issue, not a ShardingSphere bug.
- If backend is PostgreSQL, use a PostgreSQL client and set
proxy-frontend-database-protocol-type: PostgreSQL in the repository (e.g., via
DistSQL ALTER PROXY
PROPERTIES('proxy-frontend-database-protocol-type'='PostgreSQL'); then restart)
or during initial setup.
- If you need MySQL protocol, only use MySQL-dialect backends;
cross-dialect (MySQL protocol to PostgreSQL backend) is unsupported and will
error.
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