docs: update the installation guide and admin notes (close #10957)

docs/install.md

@@ -361,7 +361,9 @@ In this instruction, we use [Caddy](https://caddyserver.com/) to make the Firefi
     sudo systemctl enable --now firefish
     ```
 
-## Upgrading
+## Maintain the server
+
+### Upgrade Firefish version
 
 Please refer to the [upgrade instruction](./upgrade.md). Be sure to switch to `firefish` user and go to the Firefish directory before executing the `git` command:
 
@@ -370,6 +372,77 @@ sudo su --login firefish
 cd ~/firefish
 ```
 
+### Rotate logs
+
+If the server runs long, the size of log files increases, filling up disk space. To prevent this, you should set up a log rotation (removing old logs automatically).
+
+You can edit the `SystemMaxUse` value in the `[journal]` section of `/etc/systemd/journald.conf` to do it:
+
+```conf
+[journal]
+... (omitted)
+SystemMaxUse=500M
+...
+```
+
+Make sure to remove the leading `#` to uncomment the line. After editing the config file, you need to restart `systemd-journald` service.
+
+```sh
+sudo systemctl restart systemd-journald
+```
+
+It is also recommended that you change the [PGroonga log level](https://pgroonga.github.io/reference/parameters/log-level.html). The default level is `notice`, but this is too verbose for daily use.
+
+To control the log level, add this line to your `postgresql.conf`:
+
+```conf
+pgroonga.log_level = error
+```
+
+You can check the `postgresql.conf` location by this command:
+
+```sh
+psql --user postgres --command 'SHOW config_file'
+```
+
+The PGroonga log file (`pgroonga.log`) is located under this directory:
+
+```sh
+psql --user postgres --command 'SHOW data_directory'
+```
+
+### Tune database configuration
+
+The default PostgreSQL configuration not suitable for running a Firefish server. Thus, it is highly recommended that you use [PGTune](https://pgtune.leopard.in.ua/) to tweak the configuration.
+
+Here is an example set of parameters you can provide to PGTune:
+
+|             Parameter | Value                                                   |
+|----------------------:|---------------------------------------------------------|
+|            DB version | 16 (your PostgreSQL major version)                      |
+|               OS Type | Linux                                                   |
+|               DB Type | Data warehouse                                          |
+|          Total Memory | (total physical memory) - 700 MB                        |
+|        Number of CPUs | number of CPU threads (or lower value if you have many) |
+| Number of connections | 200                                                     |
+|          Data storage | SSD storage                                             |
+
+Since this is not a dedicated database server, be sure to leave some memory space for other software such as Firefish and Redis.
+
+Once you have entered the appropriate values for your environment, click the "Generate" button to generate a configuration and replace the values in `postgresql.conf` with the suggested values.
+
+### VACUUM your database
+
+If the database runs long, "garbage" can degrade its performance or cause problems. To prevent this, you should execute the following commands regularly.
+
+```sh
+sudo systemctl stop firefish
+sudo --user=postgres psql --dbname=firefish_db --command='VACUUM FULL VERBOSE ANALYZE'
+sudo systemctl start firefish
+```
+
+Note that this operation takes some time.
+
 ## Customize
 
 - To add custom CSS for all users, edit `./custom/assets/instance.css`.

docs/notice-for-admins.md

@@ -6,6 +6,10 @@ You can skip intermediate versions when upgrading from an old version, but pleas
 
 Please take a look at #10947.
 
+## Unreleased
+
+This is not related to the recent changes, but we have added a new subsection called "[Maintain the server](https://firefish.dev/firefish/firefish/-/blob/develop/docs/install.md#maintain-the-server)" in the installation guide. We suggest that you take a look at it.
+
 ## v20240607
 
 The following environment variables are deprecated and no longer have any effect: