babelfish for postgresql 分析--babelfishpg_tds--doing
babelfishpg_tds插件 支持了TDS 协议扩展，实现 TDS 客户端-服务器协议
先看插件加载时的函数
void
_PG_init(void)
{//是否已加载static bool inited = false;if (inited)return;//tds插件必须在shared_preload_libraries中，在数据库启动时即加载if (!process_shared_preload_libraries_in_progress)ereport(ERROR, (errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),errmsg("babelfishpg_tds must be loaded via shared_preload_libraries")));//初始化guc参数，见下表TdsDefineGucs();//创建了一个插件ptr，暂时未看到具体使用tds_instr_plugin_ptr = (TdsInstrPlugin **) find_rendezvous_variable("TdsInstrPlugin");//初始化端口监听等，在postgresql中实现tds协议的核心pe_init();//内核中新增了relname_lookup_hook hook，返回保存在tvp_lookup_list中的relidprev_relname_lookup_hook = relname_lookup_hook;relname_lookup_hook = tvp_lookup;/* Shmem hooks *///共享内存中创建TdsStatus，保存每个连接tds的状况next_shmem_startup_hook = shmem_startup_hook;shmem_startup_hook = tds_status_shmem_startup;prev_shmem_request_hook = shmem_request_hook;shmem_request_hook = tds_shmem_request;/* Install our object_access_hook into the chain */next_object_access_hook = object_access_hook;//object_access_hook，主要检查是否有权限drop userobject_access_hook = babelfish_object_access;/* Install our process utility hook into the chain */next_ProcessUtility = ProcessUtility_hook;//Utility hook，用于在执行ddl前做额外的权限检查，检查的语句有DropRoleStmt，T_RenameStmt，T_DropdbStmt，T_AlterRoleStmt，T_AlterRoleSetStmt，T_GrantRoleStmt，在执行完检查后执行正常的ProcessUtility，通过调用next_ProcessUtility ProcessUtility_hook = tdsutils_ProcessUtility;inited = true;
}
新增guc参数
| 参数 | GucContext | 说明 | 默认值 |
|---|---|---|---|
| babelfishpg_tds.port | PGC_POSTMASTER(数据库启动时设置) | tds监听的端口 | 1433 |
| babelfishpg_tds.listen_addresses | PGC_POSTMASTER(数据库启动时设置) | tds监听的ip | * |
| babelfishpg_tds.unix_socket_directories | PGC_POSTMASTER(数据库启动时设置) | TDS server unix socket directories | NULL |
| babelfishpg_tds.unix_socket_permissions | PGC_POSTMASTER(数据库启动时设置) | TDS server unix socket permissions | 0777 |
| babelfishpg_tds.unix_socket_group | PGC_POSTMASTER | TDS server unix socket group. | NULL |
| babelfishpg_tds.default_server_name | PGC_SIGHUP(数据库启动时设置或者reload触发中断设置) | 默认server name | Microsoft SQL Server |
| babelfishpg_tds.product_version | PGC_USERSET(用户可修改) | Product Version returned by Babelfish | default |
| babelfishpg_tds.tds_default_numeric_precision | PGC_SIGHUP | 默认numeric精度 | 38 |
| babelfishpg_tds.tds_default_numeric_scale | PGC_SIGHUP | 默认numeric范围 | 8 |
| babelfishpg_tds.tds_ssl_encrypt | PGC_SIGHUP | ssl加密开关 | false |
| babelfishpg_tds.tds_default_protocol_version | PGC_SIGHUP | tds协议版本 | TDS_DEFAULT_VERSION |
| babelfishpg_tds.tds_ssl_max_protocol_version | PGC_SIGHUP | ssl协议最大版本 | PG_TLS1_2_VERSION |
| babelfishpg_tds.tds_ssl_min_protocol_version | PGC_SIGHUP | ssl协议最小版本 | PG_TLS1_VERSION |
| babelfishpg_tds.tds_default_packet_size | PGC_SIGHUP | 发送的packet大小 | 4096 |
| babelfishpg_tds.tds_debug_log_level | PGC_SIGHUP | 日志级别 | 1 |
| enable_drop_babelfish_role | PGC_USERSET | 是否可以删除一个babelfish role | false |
| babelfishpg_tds.trigger_fault_enabled | PGC_SUSET | Enable fault injection triggers | true |