dumpling: merge userguide into docs

dumpling-overview.md

@@ -411,3 +411,38 @@
 | `--tidb-mem-quota-query`     | The memory limit of exporting SQL statements by a single line of Dumpling command, and the unit is byte. For v4.0.10 or later versions, if you do not set this parameter, TiDB uses the value of the `mem-quota-query` configuration item as the memory limit value by default. For versions earlier than v4.0.10, the parameter value defaults to 32 GB.  | 34359738368 |
 | `--params`                   | Specifies the session variable for the connection of the database to be exported. The required format is `"character_set_client=latin1,character_set_connection=latin1"`                                                                                                                                                           |
 |  `-c` or `--compress` |  Compresses the CSV and SQL data and table structure files exported by Dumpling. It supports the following compression algorithms: `gzip`, `snappy`, and `zstd`.  | "" |
+
+## Output filename template
+
+The `--output-filename-template` argument defines the naming convention for output files, excluding the file extensions. It accepts strings in the [Go `text/template` syntax](https://golang.org/pkg/text/template/).
+
+The following fields are available for the template:
+
+* `.DB`: the database name
+* `.Table`: the table name or the object name
+* `.Index`: the 0-based sequence number of the file when a table is split into multiple files, indicating which part is being dumped. For example, `{{printf "%09d" .Index}}` means formatting `.Index` as a 9-digit number with leading zeros.
+
+Database and table names might contain special characters (such as `/`) that are not allowed in file systems. To handle this issue, Dumpling provides the `fn` function to percent-encode these special characters:
+
+* U+0000 to U+001F (control characters)
+* `/`, `\`, `<`, `>`, `:`, `"`, `*`, `?` (invalid Windows path characters)
+* `.` (database or table name separator)
+* `-`, if used as part of `-schema`
+
+For example, using `--output-filename-template '{{fn .Table}}.{{printf "%09d" .Index}}'`, Dumpling will write the table `db.tbl:normal` into files named `tbl%3Anormal.000000000.sql`, `tbl%3Anormal.000000001.sql`, and so on.
+
+In addition to output data files, you can define `--output-filename-template` to replace file names of the schema files. The following table shows the default configurations.
+
+| Name | Content |
+|------|---------|
+| data | `{{fn .DB}}.{{fn .Table}}.{{.Index}}` |
+| schema | `{{fn .DB}}-schema-create` |
+| table | `{{fn .DB}}.{{fn .Table}}-schema` |
+| event | `{{fn .DB}}.{{fn .Table}}-schema-post` |
+| function | `{{fn .DB}}.{{fn .Table}}-schema-post` |
+| procedure | `{{fn .DB}}.{{fn .Table}}-schema-post` |
+| sequence | `{{fn .DB}}.{{fn .Table}}-schema-sequence` |
+| trigger | `{{fn .DB}}.{{fn .Table}}-schema-triggers` |
+| view | `{{fn .DB}}.{{fn .Table}}-schema-view` |
+
+For example, using `--output-filename-template '{{define "table"}}{{fn .Table}}.$schema{{end}}{{define "data"}}{{fn .Table}}.{{printf "%09d" .Index}}{{end}}'`, Dumpling will write the schema of the table `db.tbl:normal` into a file named `tbl%3Anormal.$schema.sql`, and write the data into files `tbl%3Anormal.000000000.sql`, `tbl%3Anormal.000000001.sql`, and so on.