Added ch flows export to file before ttl delete #9398 (#9427)

* Added ch flows export to file before ttl delete. Need to add pref for path getter

* Added clickhouse ttl export path pref

* Fixed naming in clickhouse flow archive

* Updated naming in clickhouse flow archive pref

* Removed clickhouse archive path pref

* Added IXP mode pref #9421

* Removed unused prefs ch flows archive

doc/developers/README.Add_startup_param.md

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+# Adding New Startup Parameters in ntopng
+
+This guide explains how to add a new command-line startup parameter to ntopng, using the `--db-archive-dir` parameter implementation as a reference example.
+
+## Overview
+
+Adding a new startup parameter in ntopng requires modifications to three main files:
+- `include/Prefs.h` - Header file containing the Prefs class declaration
+- `src/Prefs.cpp` - Implementation of preferences handling and command-line parsing
+- `src/LuaEngineNtop.cpp` - Lua engine integration (if the parameter needs to be accessible from Lua scripts)
+
+## Step 1: Modify the Header File (`include/Prefs.h`)
+
+### 1.1 Add the Member Variable
+
+Add a new member variable to store the parameter value in the private section of the `Prefs` class:
+
+```cpp
+char *data_dir, *install_dir, *docs_dir, *scripts_dir, *callbacks_dir,
+    *pcap_dir, *clickhouse_archive_dir  // Add your new parameter here
+```
+
+### 1.2 Add the Getter Method
+
+Add a public getter method to access the parameter value:
+
+```cpp
+inline const char* get_clickhouse_archive_dir() { return (clickhouse_archive_dir); };
+```
+
+**Note**: Use `inline const char*` for string parameters that return directory paths or simple string values.
+
+## Step 2: Modify the Implementation File (`src/Prefs.cpp`)
+
+### 2.1 Initialize the Member Variable
+
+In the `Prefs::Prefs(Ntop *_ntop)` constructor, initialize your new member variable to `NULL`:
+
+```cpp
+pcap_dir = NULL;
+clickhouse_archive_dir = NULL;  // Add initialization here
+```
+
+### 2.2 Add Memory Cleanup
+
+In the `Prefs::~Prefs()` destructor, add memory cleanup for your parameter:
+
+```cpp
+if(pcap_dir) free(pcap_dir);
+if(clickhouse_archive_dir) free(clickhouse_archive_dir);  // Add cleanup here
+```
+
+### 2.3 Update the Usage Function
+
+Add your parameter's documentation to the `usage()` function:
+
+```cpp
+"[--db-archive-dir|-6] <path>        | Directory used for archiving historical flows\n"
+"                                    | recorded on ClickHouse when data retention is over.\n"
+"                                    | Default: %s\n"
+```
+
+Make sure to add the corresponding format argument in the printf-style call:
+
+```cpp
+CONST_DEFAULT_DOCS_DIR, CONST_DEFAULT_SCRIPTS_DIR,
+CONST_DEFAULT_CALLBACKS_DIR, CONST_DEFAULT_DATA_DIR,
+CONST_DEFAULT_DATA_DIR,  // Add default value here
+```
+
+### 2.4 Add Long Option Definition
+
+Add your parameter to the `long_options` array:
+
+```cpp
+{"pcap-dir",                required_argument, NULL, '5'},
+{"db-archive-dir",          required_argument, NULL, '6'},  // Add your option here
+```
+
+**Important**: 
+- Use a unique single character (like '6') for the option identifier
+- Set `required_argument` if the parameter requires a value
+- Set `no_argument` if it's a boolean flag
+
+### 2.5 Update the Option String
+
+Add your option character to the option string in `loadFromCLI()`:
+
+```cpp
+"k:eg:hi:w:r:sg:m:n:p:qd:t:x:y:1:2:3:4:5:6:l:L:uv:zA:B:c:CD:E:F:MN:G:I:O:Q:"
+//                                        ^ Add your character here
+```
+
+**Note**: Add `:` after the character if the parameter requires an argument.
+
+### 2.6 Implement Option Handling
+
+Add a case in the `setOption()` function to handle your parameter:
+
+```cpp
+case '6':
+  if(clickhouse_archive_dir) free(clickhouse_archive_dir);
+  clickhouse_archive_dir = strdup(optarg);
+  break;
+```
+
+### 2.7 Add Default Value Assignment
+
+In the `checkOptions()` function, set a default value if none was provided:
+
+```cpp
+if(!pcap_dir) pcap_dir = strdup(ntop->get_working_dir());
+if(!clickhouse_archive_dir) clickhouse_archive_dir = strdup(ntop->get_working_dir());
+```
+
+### 2.8 Add Path Validation
+
+Add path validation for directory parameters:
+
+```cpp
+docs_dir = ntop->getValidPath(docs_dir);
+scripts_dir = ntop->getValidPath(scripts_dir);
+callbacks_dir = ntop->getValidPath(callbacks_dir);
+pcap_dir = ntop->getValidPath(pcap_dir);
+clickhouse_archive_dir = ntop->getValidPath(clickhouse_archive_dir);
+```
+
+### 2.9 Add Directory Existence Check
+
+Add validation to ensure the directory exists:
+
+```cpp
+if(!pcap_dir[0]) {
+  ntop->getTrace()->traceEvent(TRACE_ERROR, "Unable to locate pcap dir");
+  return (-1);
+}
+if(!clickhouse_archive_dir[0]) {
+  ntop->getTrace()->traceEvent(TRACE_ERROR, "Unable to locate ClickHouse archive dir");
+  return (-1);
+}
+```
+
+### 2.10 Add Trailing Slash Removal
+
+Remove trailing slashes from directory paths:
+
+```cpp
+ntop->removeTrailingSlash(docs_dir);
+ntop->removeTrailingSlash(scripts_dir);
+ntop->removeTrailingSlash(callbacks_dir);
+ntop->removeTrailingSlash(pcap_dir);
+ntop->removeTrailingSlash(clickhouse_archive_dir);
+```
+
+## Step 3: Add Lua Integration (Optional)
+
+If your parameter needs to be accessible from Lua scripts, modify `src/LuaEngineNtop.cpp`:
+
+### 3.1 Update the `ntop_get_dirs()` Function
+
+Add your parameter to the Lua table in the `ntop_get_dirs()` function:
+
+```cpp
+lua_push_str_table_entry(vm, "callbacksdir",
+                         ntop->getPrefs()->get_callbacks_dir());
+lua_push_str_table_entry(vm, "pcapdir", ntop->getPrefs()->get_pcap_dir());
+lua_push_str_table_entry(vm, "dbarchivedir", ntop->getPrefs()->get_clickhouse_archive_dir());
+```
+
+**Note**: Use a descriptive key name (like "dbarchivedir") that will be used in Lua scripts.
+
+## Best Practices
+
+### Parameter Naming
+- Use descriptive, kebab-case names for long options (e.g., `--db-archive-dir`)
+- Choose meaningful single characters for short options
+- Avoid conflicts with existing parameters
+
+### Memory Management
+- Always initialize pointers to `NULL` in the constructor
+- Always free allocated memory in the destructor
+- Use `strdup()` to copy string arguments
+- Check for existing values before reassigning (free first)
+
+### Validation
+- Validate directory paths using `ntop->getValidPath()`
+- Check directory existence and accessibility
+- Provide meaningful error messages
+- Set sensible default values
+
+### Documentation
+- Add comprehensive usage text explaining the parameter's purpose
+- Include default values in the usage text
+- Use consistent formatting with existing parameters
+
+## Testing
+
+After implementing your new parameter:
+
+1. **Compile ntopng** to ensure no syntax errors
+2. **Test the help output**: `./ntopng --help` should show your new parameter
+3. **Test with the parameter**: `./ntopng --db-archive-dir /path/to/archive`
+4. **Test without the parameter** to ensure defaults work
+5. **Test invalid paths** to ensure error handling works
+6. **Test Lua integration** (if applicable) by accessing the parameter from Lua scripts
+
+## Example Usage
+
+Once implemented, the parameter can be used as:
+
+```bash
+# Long form
+./ntopng --db-archive-dir /var/lib/ntopng/archive
+
+# Short form  
+./ntopng -6 /var/lib/ntopng/archive
+```
+
+And accessed from Lua scripts as:
+
+```lua
+local dirs = ntop.getDirs()
+local archive_dir = dirs["dbarchivedir"]
+```