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Merge pull request #29445 from taosdata/docs/FAQ 

docs: add 33~35 FAQ problem
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Shengliang Guan 2025-01-01 21:00:38 +08:00 committed by GitHub
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19
docs/en/27-train-faq/index.md
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@ -297,3 +297,22 @@ Reporting this error indicates that the first connection to the cluster was succ
Therefore, first, check whether all ports on the server and cluster (default 6030 for native connections and 6041 for HTTP connections) are open; Next, check if the client's hosts file has configured the fqdn and IP information for all dnodes in the cluster.
If the issue still cannot be resolved, it is necessary to contact Taos technical personnel for support.
### 32 Why is the original database lost and the cluster ID changed when the data directory dataDir of the database remains unchanged on the same server?
Background: When the TDengine server process (taosd) starts, if there are no valid data file subdirectories (such as mnode, dnode, and vnode) under the data directory (dataDir, which is specified in the configuration file taos.cfg), these directories will be created automatically.When a new mnode directory is created, a new cluster ID will be allocated to generate a new cluster.
Cause analysis: The data directory dataDir of taosd can point to multiple different mount points.If these mount points are not configured for automatic mounting in the fstab file, after the server restarts, dataDir will only exist as a normal directory of the local disk, and it will not point to the mounted disk as expected.At this point, if the taosd service is started, it will create a new directory under dataDir to generate a new cluster.
Impact of the problem: After the server is restarted, the original database is lost (note: it is not really lost, but the original data disk is not attached and cannot be seen for the time being) and the cluster ID changes, resulting in the inability to access the original database. For enterprise users, if they have been authorized for the cluster ID, they will also find that the machine code of the cluster server has not changed, but the original authorization has expired.If the problem is not monitored or found and handled in time, the user will not notice that the original database has been lost, resulting in losses and increased operation and maintenance costs.
Problem solving: You should configure the automatic mount of the dataDir directory in the fstab file to ensure that the dataDir always points to the expected mount point and directory. At this point, restarting the server will retrieve the original database and cluster. In the subsequent version, we will develop a function to enable taosd to exit in the startup phase when it detects that the dataDir changes before and after startup, and provide corresponding error prompts.
### 33 How to solve MVCP1400.DLL loss when running TDengine on Windows platform?
1. Reinstall Microsoft Visual C++ Redistributable: As msvcp140.dll is part of Microsoft Visual C++Redistributable, reinstalling this package usually resolves most issues. You can download the corresponding version from the official Microsoft website for installation
2. Manually download and replace the msvcp140.dll file online: You can download the msvcp140.dll file from a reliable source and copy it to the corresponding directory in the system. Ensure that the downloaded files match your system architecture (32-bit or 64 bit) and ensure the security of the source
### 34 Which fast query data from super table with TAG filter or child table ?
Directly querying from child table is fast. The query from super table with TAG filter is designed to meet the convenience of querying. It can filter data from multiple child tables at the same time. If the goal is to pursue performance and the child table has been clearly queried, directly querying from the sub table can achieve higher performance
### 35 How to view data compression ratio indicators?
Currently, TDengine only provides compression ratios based on tables, not databases or the entire system. To view the compression ratios, execute the `SHOW TABLE DISTRIBUTED table_name;` command in the client taos-CLI. The table_name can be a super table, regular table, or subtable. For details [Click Here](https://docs.tdengine.com/tdengine-reference/sql-manual/show-commands/#show-table-distributed)

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docs/zh/27-train-faq/01-faq.md
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@ -302,3 +302,13 @@ TDinsight插件中展示的数据是通过taosKeeper和taosAdapter服务收集
问题影响：服务器重启后，原有数据库丢失（注：并非真正丢失，只是原有的数据磁盘未挂载，暂时看不到）且集群 ID 发生变化，导致无法访问原有数据库。对于企业版用户，如果已针对集群 ID 进行授权，还会发现集群服务器的机器码未变，但原有的授权已失效。如果未针对该问题进行监控或者未及时发现并进行处理，则用户不会注意到原有数据库已经丢失，从而造成损失，增加运维成本。
问题解决：应在 fstab 文件中配置 dataDir 目录的自动挂载，确保 dataDir 始终指向预期的挂载点和目录，此时，再重启服务器，会找回原有的数据库和集群。在后续的版本中，我们将开发一个功能，使 taosd 在检测到启动前后 dataDir 发生变化时，在启动阶段退出，同时提供相应的错误提示。
### 33 Windows 平台运行 TDengine 出现丢失 MVCP1400.DLL 解决方法？
1. 重新安装 Microsoft Visual C++ Redistributable‌：由于 msvcp140.dll 是 Microsoft Visual C++ Redistributable 的一部分，重新安装这个包通常可以解决大部分问题。可以从 Microsoft 官方网站下载相应的版本进行安装‌
2. 手动上网下载并替换 msvcp140.dll 文件‌：可以从可靠的源下载 msvcp140.dll 文件，并将其复制到系统的相应目录下。确保下载的文件与您的系统架构（32位或64位）相匹配，并确保来源的安全性‌
### 34 超级表带 TAG 过滤查子查数据与直接查子表哪个块？
直接查子表更快。超级表带 TAG 过滤查询子查数据是为满足查询方便性，同时可对多个子表中数据进行过滤，如果目的是追求性能并已明确查询子表，直接从子表查性能更高
### 35 如何查看数据压缩率指标？
TDengine 目前只提供以表为统计单位的压缩率，数据库及整体还未提供，查看命令是在客户端 taos-CLI 中执行 `SHOW TABLE DISTRIBUTED table_name;` 命令，table_name 为要查看压缩率的表，可以为超级表、普通表及子表，详细可 [查看此处](https://docs.taosdata.com/reference/taos-sql/show/#show-table-distributed)