Java MariaDB JDBC socket error with ProxySQL: unexpected end of stream / Unexpected packet from client during Hibernate update flow

[balajibabu-eng]

Hi Team,

We are facing intermittent Java/JDBC socket errors after routing application traffic through ProxySQL.

Environment:

• ProxySQL version: 3.0.8-481-g0ef544c
• OS: Ubuntu 24.04
• Backend DB: MariaDB 11.8.6
• JDBC driver: org.mariadb.jdbc.Driver
• Application framework: Spring Boot / Hibernate / HikariCP
• Topology: Application -> Load Balancer -> ProxySQL -> MariaDB
• ProxySQL frontend port: 6033
• Backend writer hostgroup: 10
• Reader hostgroup: 20
• mysql-multiplexing: true
• mysql-enable_server_deprecate_eof: true
• Application uses Hibernate batching: yes

Issue:
After routing Java application traffic through ProxySQL, normal DB connectivity works, and simple SELECT/INSERT/UPDATE queries succeed. However, during application create/update flows, the application intermittently fails with JDBC socket errors.

Application-side error:

java.sql.SQLNonTransientConnectionException: Socket error

Caused by:

java.io.EOFException: unexpected end of stream, read 0 bytes from 4 (socket was closed by server)

ProxySQL log shows:

MySQL_Session.cpp:4808:handler___status_NONE_or_default(): [ERROR] Unexpected packet from client <app_client_ip>. Session_status: 6 , client_status: 0 Disconnecting it

Also:

MySQL_Thread.cpp:4398:ProcessAllSessions_Healthy0(): [WARNING] Closing unhealthy client connection <app_client_ip>:

Validation already done:

1. Direct connection to ProxySQL frontend works.
2. SELECT through ProxySQL works.
3. INSERT through ProxySQL works.
4. UPDATE through ProxySQL works.
5. Transaction + rollback through ProxySQL works.
6. Same DB-level tests through Load Balancer -> ProxySQL also work.
7. ProxySQL monitor logs show backend servers healthy.
8. No backend MariaDB connection errors during simple DB tests.

The issue appears only during full Java/Hibernate application flows, especially create/update order operations.

Question:
Is this a known issue with ProxySQL multiplexing and Java/Hibernate/MariaDB JDBC batching?
Is disabling multiplexing for the affected application user the recommended approach, or should Hibernate batching be disabled instead?

[coderabbitai]

⚠️ Possible Duplicate Issue(s)

• ProxySQL 3.0.7 — Breaking Change with rewriteBatchedStatements / Batch Query Mode #5672

🔗 Related PRs

#5559 - Fix crash when COM_BINLOG_DUMP received with idle backends (#5556) [merged]

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[balajibabu-eng]

@renecannao This issue has been marked as duplicate however, in the issue 5672 proxysql version was 3.7 and we are facing the same issue in 3.0.8-481-g0ef544c as well.. Is there a fix/change on the proxysql end? or reinstalling any of the older versions will be helpful in this scenario?

[renecannao]

Client sees connection died:

java.io.EOFException: unexpected end of stream, read 0 bytes from 4 (socket was closed by server)

ProxySQL sees connection died:

MySQL_Session.cpp:4808:handler___status_NONE_or_default(): [ERROR] Unexpected packet from client <app_client_ip>. Session_status: 6 , client_status: 0 Disconnecting it
MySQL_Thread.cpp:4398:ProcessAllSessions_Healthy0(): [WARNING] Closing unhealthy client connection <app_client_ip>:

Both client and proxysql reports that socket closed for no apparent reason.
Considering the topology (Application -> Load Balancer -> ProxySQL -> MariaDB) , I bet on load balancer closing the connection because of some timeout.
You can try to tune mysql-use_tcp_keepalive and mysql-tcp_keepalive_time , but this is unlikely a ProxySQL issue unless proven otherwise.