数据库路由中间件MyCat - 源代码篇（15）
此文已由作者张镐薪授权网易云社区发布。
欢迎访问网易云社区，了解更多网易技术产品运营经验。
public static void handle(String stmt, ServerConnection c, int offs) {
int offset = offs;
switch (ServerParseSelect.parse(stmt, offs)) {
case ServerParseSelect.VERSION_COMMENT:
SelectVersionComment.response(c);
break;
case ServerParseSelect.DATABASE:
SelectDatabase.response(c);
break;
case ServerParseSelect.USER:
SelectUser.response(c);
break;
case ServerParseSelect.VERSION:
SelectVersion.response(c);
break;
case ServerParseSelect.SESSION_INCREMENT:
SessionIncrement.response(c);
break;
case ServerParseSelect.SESSION_ISOLATION:
SessionIsolation.response(c);
break;
case ServerParseSelect.LAST_INSERT_ID:
// offset = ParseUtil.move(stmt, 0, "select".length());
loop:for (int l=stmt.length(); offset < l; ++offset) {
switch (stmt.charAt(offset)) {
case ' ':
continue;
case '/':
case '#':
offset = ParseUtil.comment(stmt, offset);
continue;
case 'L':
case 'l':
break loop;
}
}
offset = ServerParseSelect.indexAfterLastInsertIdFunc(stmt, offset);
offset = ServerParseSelect.skipAs(stmt, offset);
SelectLastInsertId.response(c, stmt, offset);
break;
case ServerParseSelect.IDENTITY:
// offset = ParseUtil.move(stmt, 0, "select".length());
loop:for (int l=stmt.length(); offset < l; ++offset) {
switch (stmt.charAt(offset)) {
case ' ':
continue;
case '/':
case '#':
offset = ParseUtil.comment(stmt, offset);
continue;
case '@':
break loop;
}
}
int indexOfAtAt = offset;
offset += 2;
offset = ServerParseSelect.indexAfterIdentity(stmt, offset);
String orgName = stmt.substring(indexOfAtAt, offset);
offset = ServerParseSelect.skipAs(stmt, offset);
SelectIdentity.response(c, stmt, offset, orgName);
break;
case ServerParseSelect.SELECT_VAR_ALL:
SelectVariables.execute(c,stmt);
break;
default:
c.execute(stmt, ServerParse.SELECT);
}
}下一步，ServerConnection类处理SQL语句
ServerConnection.java
public void execute(String sql, int type) { //连接状态检查
if (this.isClosed()) {
LOGGER.warn("ignore execute ,server connection is closed " + this); return;
} // 事务状态检查
if (txInterrupted) {
writeErrMessage(ErrorCode.ER_YES, "Transaction error, need to rollback." + txInterrputMsg); return;
} // 检查当前使用的DB
String db = this.schema; if (db == null) {
db = SchemaUtil.detectDefaultDb(sql, type); if (db == null) {
writeErrMessage(ErrorCode.ERR_BAD_LOGICDB, "No MyCAT Database selected"); return;
}
} // 兼容PhpAdmin's, 支持对MySQL元数据的模拟返回
//// TODO: 2016/5/20 支持更多information_schema特性
if (ServerParse.SELECT == type
&& db.equalsIgnoreCase("information_schema") ) {
MysqlInformationSchemaHandler.handle(sql, this); return;
} if (ServerParse.SELECT == type
&& sql.contains("mysql")
&& sql.contains("proc")) {
SchemaUtil.SchemaInfo schemaInfo = SchemaUtil.parseSchema(sql); if (schemaInfo != null
&& "mysql".equalsIgnoreCase(schemaInfo.schema)
&& "proc".equalsIgnoreCase(schemaInfo.table)) { // 兼容MySQLWorkbench
MysqlProcHandler.handle(sql, this); return;
}
}
SchemaConfig schema = MycatServer.getInstance().getConfig().getSchemas().get(db); if (schema == null) {
writeErrMessage(ErrorCode.ERR_BAD_LOGICDB, "Unknown MyCAT Database '" + db + "'"); return;
}
routeEndExecuteSQL(sql, type, schema);
}调用routeEndExecuteSQL方法，会解析出RouteResultSet。这步包含了SQL语义解析，SQL路由，SQL查询优化，SQL语句改写，全局ID生成，最后，将解析出的RouteResultSet交给这个链接对应的session进行处理。 我们先分析SQL语义解析。看调用： ServerConnection.java
rrs = MycatServer .getInstance() .getRouterservice() .route(MycatServer.getInstance().getConfig().getSystem(), schema, type, sql, this.charset, this);
首先，关注下这个Routerservice是啥？在MyCat初始化时，会新建一个Routerservice（如之前配置模块中所讲）： MyCatServer.java
//路由计算初始化routerService = new RouteService(cacheService);
Routerservice结构： 其中sqlRouteCache和tableId2DataNodeCache是通过CacheService（MyCat里面是ehcache做的缓存）传入的对于sql语句缓存和tableid与后台分片对应关系的缓存。具体缓存会在缓存模块中讲。
调用route方法解析出RouteResultSet
public RouteResultset route(SystemConfig sysconf, SchemaConfig schema, int sqlType, String stmt, String charset, ServerConnection sc)
throws SQLNonTransientException {
RouteResultset rrs = null;
String cacheKey = null; /**
* SELECT 类型的SQL, 检测
*/
if (sqlType == ServerParse.SELECT) {
cacheKey = schema.getName() + stmt;
rrs = (RouteResultset) sqlRouteCache.get(cacheKey); if (rrs != null) { return rrs;
}
} /*!mycat: sql = select name from aa */
/*!mycat: schema = test */// boolean isMatchOldHint = stmt.startsWith(OLD_MYCAT_HINT);// boolean isMatchNewHint = stmt.startsWith(NEW_MYCAT_HINT);// if (isMatchOldHint || isMatchNewHint ) {
int hintLength = RouteService.isHintSql(stmt); if(hintLength != -1){ int endPos = stmt.indexOf("*/"); if (endPos > 0) {
// 用!mycat:内部的语句来做路由分析// int hintLength = isMatchOldHint ? OLD_MYCAT_HINT.length() : NEW_MYCAT_HINT.length();
String hint = stmt.substring(hintLength, endPos).trim();
int firstSplitPos = hint.indexOf(HINT_SPLIT);
if(firstSplitPos > 0 ){
Map hintMap= parseHint(hint);
String hintType = (String) hintMap.get(MYCAT_HINT_TYPE);
String hintSql = (String) hintMap.get(hintType); if( hintSql.length() == 0 ) {
LOGGER.warn("comment int sql must meet :/*!mycat:type=value*/ or /*#mycat:type=value*/ or /*mycat:type=value*/: "+stmt); throw new SQLSyntaxErrorException("comment int sql must meet :/*!mycat:type=value*/ or /*#mycat:type=value*/ or /*mycat:type=value*/: "+stmt);
}
String realSQL = stmt.substring(endPos + "*/".length()).trim();
HintHandler hintHandler = HintHandlerFactory.getHintHandler(hintType); if( hintHandler != null ) {
if ( hintHandler instanceof HintSQLHandler) {
/**
* 修复 注解SQL的 sqlType 与 实际SQL的 sqlType 不一致问题， 如： hint=SELECT，real=INSERT
* fixed by zhuam
*/
int hintSqlType = ServerParse.parse( hintSql ) & 0xff;
rrs = hintHandler.route(sysconf, schema, sqlType, realSQL, charset, sc, tableId2DataNodeCache, hintSql,hintSqlType,hintMap);
} else {
rrs = hintHandler.route(sysconf, schema, sqlType, realSQL, charset, sc, tableId2DataNodeCache, hintSql,sqlType,hintMap);
}
}else{
LOGGER.warn("TODO , support hint sql type : " + hintType);
}
}else{//fixed by runfriends@126.com
LOGGER.warn("comment in sql must meet :/*!mycat:type=value*/ or /*#mycat:type=value*/ or /*mycat:type=value*/: "+stmt); throw new SQLSyntaxErrorException("comment in sql must meet :/*!mcat:type=value*/ or /*#mycat:type=value*/ or /*mycat:type=value*/: "+stmt);
}
}
} else {
stmt = stmt.trim();
rrs = RouteStrategyFactory.getRouteStrategy().route(sysconf, schema, sqlType, stmt,
charset, sc, tableId2DataNodeCache);
} if (rrs != null && sqlType == ServerParse.SELECT && rrs.isCacheAble()) {
sqlRouteCache.putIfAbsent(cacheKey, rrs);
} return rrs;
}由于注解处理和sql解析有重叠，而且注解处理一直代码不稳定，所以，这里不涉及。只说sql正常解析的步骤
更多网易技术、产品、运营经验分享请点击。
相关文章：
【推荐】 Redux其实很简单（原理篇）
