Cache startup queries

docs/config.md

@@ -733,6 +733,21 @@ out [this discussion on Reddit](https://www.reddit.com/r/golang/comments/r9u4ee/
 
 Depending on *how you run it*, here are a few limits that are relevant:
 
+### WAL for message cache
+By default, the [message cache](#message-cache) (defined by `cache-file`) uses the SQLite default settings, which means it
+syncs to disk on every write. For personal servers, this is perfectly adequate. For larger installations, such as ntfy.sh,
+the [write-ahead log (WAL)](https://sqlite.org/wal.html) should be enabled, and the sync mode should be adjusted. 
+See [this article](https://phiresky.github.io/blog/2020/sqlite-performance-tuning/) for details.
+
+Here's how ntfy.sh has been tuned in the `server.yml` file:
+
+``` yaml
+cache-startup-queries: |
+    pragma journal_mode = WAL;
+    pragma synchronous = normal;
+    pragma temp_store = memory;
+```
+
 ### For systemd services
 If you're running ntfy in a systemd service (e.g. for .deb/.rpm packages), the main limiting factor is the
 `LimitNOFILE` setting in the systemd unit. The default open files limit for `ntfy.service` is 10,000. You can override it
@@ -865,6 +880,7 @@ variable before running the `ntfy` command (e.g. `export NTFY_LISTEN_HTTP=:80`).
 | `firebase-key-file`                        | `NTFY_FIREBASE_KEY_FILE`                        | *filename*                                          | -                 | If set, also publish messages to a Firebase Cloud Messaging (FCM) topic for your app. This is optional and only required to save battery when using the Android app. See [Firebase (FCM](#firebase-fcm).                        |
 | `cache-file`                               | `NTFY_CACHE_FILE`                               | *filename*                                          | -                 | If set, messages are cached in a local SQLite database instead of only in-memory. This allows for service restarts without losing messages in support of the since= parameter. See [message cache](#message-cache).             |
 | `cache-duration`                           | `NTFY_CACHE_DURATION`                           | *duration*                                          | 12h               | Duration for which messages will be buffered before they are deleted. This is required to support the `since=...` and `poll=1` parameter. Set this to `0` to disable the cache entirely.                                        |
+| `cache-startup-queries`                    | `NTFY_CACHE_STARTUP_QUERIES`                    | *string (SQL queries)*                              | -                 | SQL queries to run during database startup; this is useful for tuning and [enabling WAL mode](#wal-for-message-cache)                                                                                                           |
 | `auth-file`                                | `NTFY_AUTH_FILE`                                | *filename*                                          | -                 | Auth database file used for access control. If set, enables authentication and access control. See [access control](#access-control).                                                                                           |
 | `auth-default-access`                      | `NTFY_AUTH_DEFAULT_ACCESS`                      | `read-write`, `read-only`, `write-only`, `deny-all` | `read-write`      | Default permissions if no matching entries in the auth database are found. Default is `read-write`.                                                                                                                             |
 | `behind-proxy`                             | `NTFY_BEHIND_PROXY`                             | *bool*                                              | false             | If set, the X-Forwarded-For header is used to determine the visitor IP address instead of the remote address of the connection.                                                                                                 |
@@ -929,6 +945,7 @@ OPTIONS:
    --behind-proxy, --behind_proxy, -P                                                                  if set, use X-Forwarded-For header to determine visitor IP address (for rate limiting) (default: false) [$NTFY_BEHIND_PROXY]
    --cache-duration since, --cache_duration since, -b since                                            buffer messages for this time to allow since requests (default: 12h0m0s) [$NTFY_CACHE_DURATION]
    --cache-file value, --cache_file value, -C value                                                    cache file used for message caching [$NTFY_CACHE_FILE]
+   --cache-startup-queries value, --cache_startup_queries value                                        queries run when the cache database is initialized [$NTFY_CACHE_STARTUP_QUERIES]
    --cert-file value, --cert_file value, -E value                                                      certificate file, if listen-https is set [$NTFY_CERT_FILE]
    --config value, -c value                                                                            config file (default: /etc/ntfy/server.yml) [$NTFY_CONFIG_FILE]
    --debug, -d                                                                                         enable debug logging (default: false) [$NTFY_DEBUG]

docs/releases.md

@@ -6,14 +6,9 @@ and the [ntfy Android app](https://github.com/binwiederhier/ntfy-android/release
 
 ## ntfy server v1.27.0 (UNRELEASED)
 
-!!! info
-    The message cache database (typically `cache.db`) now enables the write-ahead log (WAL) in SQLite.
-    WAL mode will create two additional files (`cache.db-wal` and `cache.db-shm`). This is perfectly normal.
-    Do not delete or modify these files, as that can lead to database corruption.
-
 **Features:**
 
-* Greatly improve SQLite performance for the message cache by enabling WAL mode (no ticket)
+* Add `cache-startup-queries` option to allow custom SQLite performance tuning (no ticket)
 * ntfy CLI can now [wait for a command or PID](https://ntfy.sh/docs/subscribe/cli/#wait-for-pidcommand) before publishing ([#263](https://github.com/binwiederhier/ntfy/issues/263), thanks to the [original ntfy](https://github.com/dschep/ntfy) for the idea) 
 * Trace: Log entire HTTP request to simplify debugging (no ticket)
 * Allow setting user password via `NTFY_PASSWORD` env variable ([#327](https://github.com/binwiederhier/ntfy/pull/327), thanks to [@Kenix3](https://github.com/Kenix3))