---
title: "Archive Module Callbacks"
id: archive-module-callbacks
pg_version: "20devel"
---

<a id="archive-module-callbacks"></a>

## 49.2. Archive Module Callbacks

The archive callbacks define the actual archiving behavior of the module. The server will call them as required to process each individual WAL file. 

<a id="archive-module-startup"></a>

### 49.2.1. Startup Callback

The `startup_cb` callback is called shortly after the module is loaded. This callback can be used to perform any additional initialization required. If the archive module has any state, it can use `state->private_data` to store it. 
typedef void (*ArchiveStartupCB) (ArchiveModuleState *state);
 

<a id="archive-module-check"></a>

### 49.2.2. Check Callback

The `check_configured_cb` callback is called to determine whether the module is fully configured and ready to accept WAL files (e.g., its configuration parameters are set to valid values). If no `check_configured_cb` is defined, the server always assumes the module is configured. 
typedef bool (*ArchiveCheckConfiguredCB) (ArchiveModuleState *state);
 If `true` is returned, the server will proceed with archiving the file by calling the `archive_file_cb` callback. If `false` is returned, archiving will not proceed, and the archiver will emit the following message to the server log: 
WARNING:  archive_mode enabled, yet archiving is not configured
 In the latter case, the server will periodically call this function, and archiving will proceed only when it returns `true`. 


> [!NOTE]
> When returning `false`, it may be useful to append some additional information to the generic warning message. To do that, provide a message to the `arch_module_check_errdetail` macro before returning `false`. Like `errdetail()`, this macro accepts a format string followed by an optional list of arguments. The resulting string will be emitted as the `DETAIL` line of the warning message.

<a id="archive-module-archive"></a>

### 49.2.3. Archive Callback

The `archive_file_cb` callback is called to archive a single WAL file. 
typedef bool (*ArchiveFileCB) (ArchiveModuleState *state, const char *file, const char *path);
 If `true` is returned, the server proceeds as if the file was successfully archived, which may include recycling or removing the original WAL file. If `false` is returned or an error is thrown, the server will keep the original WAL file and retry archiving later. `file` will contain just the file name of the WAL file to archive, while `path` contains the full path of the WAL file (including the file name). 


> [!NOTE]
> The `archive_file_cb` callback is called in a short-lived memory context that will be reset between invocations. If you need longer-lived storage, create a memory context in the module's `startup_cb` callback.

<a id="archive-module-shutdown"></a>

### 49.2.4. Shutdown Callback

The `shutdown_cb` callback is called when the archiver process exits (e.g., after an error) or the value of [`archive_library` (`string`)](runtime-config-wal.md#guc-archive-library) changes. If no `shutdown_cb` is defined, no special action is taken in these situations. If the archive module has any state, this callback should free it to avoid leaks. 
typedef void (*ArchiveShutdownCB) (ArchiveModuleState *state);