oblogproxy
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[Bug]: 查询全局变量时没有正确处理别名，导致获取不到server_id
Describe the bug
oblog proxy 版本： v4.2.0
这个问题在社区反馈过（https://ask.oceanbase.com/t/topic/35615629 ），没人跟进，只能来这再反馈一次。
背景是测试Maxwell抽取oblogproxy时，报错找不到server_id列。
2025-01-17 16:22:37 ERROR Maxwell - SQLException: Column 'server_id' not found.
java.sql.SQLException: Column 'server_id' not found.
at com.mysql.cj.jdbc.exceptions.SQLError.createSQLException(SQLError.java:129) ~[mysql-connector-java-8.0.28.jar:8.0.28]
at com.mysql.cj.jdbc.exceptions.SQLError.createSQLException(SQLError.java:97) ~[mysql-connector-java-8.0.28.jar:8.0.28]
at com.mysql.cj.jdbc.exceptions.SQLError.createSQLException(SQLError.java:89) ~[mysql-connector-java-8.0.28.jar:8.0.28]
at com.mysql.cj.jdbc.exceptions.SQLError.createSQLException(SQLError.java:63) ~[mysql-connector-java-8.0.28.jar:8.0.28]
at com.mysql.cj.jdbc.result.ResultSetImpl.findColumn(ResultSetImpl.java:584) ~[mysql-connector-java-8.0.28.jar:8.0.28]
at com.mysql.cj.jdbc.result.ResultSetImpl.getLong(ResultSetImpl.java:862) ~[mysql-connector-java-8.0.28.jar:8.0.28]
at com.mchange.v2.c3p0.impl.NewProxyResultSet.getLong(NewProxyResultSet.java:477) ~[c3p0-0.9.5.5.jar:0.9.5.5]
at com.zendesk.maxwell.MaxwellContext.getServerID(MaxwellContext.java:473) ~[maxwell-1.41.2.jar:1.41.2]
at com.zendesk.maxwell.MaxwellContext.<init>(MaxwellContext.java:133) ~[maxwell-1.41.2.jar:1.41.2]
at com.zendesk.maxwell.Maxwell.<init>(Maxwell.java:44) ~[maxwell-1.41.2.jar:1.41.2]
at com.zendesk.maxwell.Maxwell.main(Maxwell.java:322) [maxwell-1.41.2.jar:1.41.2]
看了maxwell的源码，maxwell在启动时会执行SQL获取server_id。
SELECT @@server_id as server_id
这个SQL返回的列名与MySQL不一致，与obproxy不开启binlog时也不一致。
开启了binlog的obproxy返回：
未开启binlog的obproxy返回：
mysql返回：
直连 obbinlog instance实例查询
基于以上可以确定是oblogproxy的bug。
我临时改了几行代码尝试修复了，供参考： https://github.com/lenmore/oblogproxy/commit/c798914977a5449344207fb5473046c655ae14c6
Environment
oblog proxy 版本： v4.2.0
Fast reproduce steps
SELECT @@server_id as server_id;
SELECT @@server_id as abc;
Expected behavior
No response
Actual behavior
No response
Additional context
No response
