terrymanu commented on issue #36966:
URL:
https://github.com/apache/shardingsphere/issues/36966#issuecomment-3471186959
## Problem Confirmation
The issue you're encountering is a protocol version mismatch when
ShardingSphere-Proxy tries to be compatible with both MySQL 5 and MySQL 8
simultaneously.
## Root Cause Analysis
Core Issue: The query_cache_size system variable has been removed in MySQL
8.0, but ShardingSphere-Proxy currently uses MySQL 5.7.22 protocol for
communication by default.
From the source code analysis, the `MySQLProtocolDefaultVersionProvider`
class returns version "5.7.22" by default. When connecting to MySQL 8, the
Proxy attempts to query system variables that no longer exist in MySQL 8,
causing connection failures.
## Compatibility Statement
Theoretical Support: ShardingSphere is designed to support both MySQL 5
and 8, but in practice, you need to consider:
- The protocol version used by Proxy determines communication with backend
databases
- Different MySQL versions support different sets of system variables
- JDBC driver compatibility also affects connection success rate
## Solution Recommendations
Option 1: Version Selection Strategy
- If primarily using MySQL 8, consider upgrading to a configuration that
supports MySQL 8 protocol
- If you need to support both versions simultaneously, consider using a
protocol version that offers better compatibility
Option 2: Architecture Adjustment
- Deploy separate Proxy instances for different MySQL versions
- Avoid having a single Proxy handle multi-version compatibility issues
Option 3: Driver Configuration
- Ensure you're using a JDBC driver version that supports MySQL 8
- Verify that your connection string configuration is correct
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