Periodically do manual checkpoints to sync the DB file with the WAL.

This is more efficient as it allows idle connections to stick around, reducing
the overhead of sporadic queries. For example, opening the first new connection
will cause creation of new WAL files (and then their subsequent deletion when
all connections are closed); this work is avoided by just keeping it open.

README.md

@@ -433,8 +433,10 @@ Additional arguments can be passed to `./SewerRat` to control its behavior (chec
 - `-update` controls the frequency of index updates.
   This defaults to 24 hours.
 - `-session` specifies the lifetime of a registration sesssion 
-  (i.e., the maximum time between starting and finishing the registration, see below).
+  (i.e., the maximum time between starting and finishing the registration, see above).
   This defaults to 10 minutes.
+- `-checkpoint` specifies the frequency of SQLite checkpoints, to manually synchronize the write-ahead log with the SQLite database file.
+  This defaults to 60 minutes.
 - `-finish` specifies the time spent polling for the verification code after a request has been made to `/register/finish` or `/deregister/finish`.
   A non-zero value is often necessary on network filesystems where newly written files do not immediately synchronize.
   This defaults to 30 seconds.

database.go

@@ -97,10 +97,6 @@ func initializeDatabase(path string) (*sql.DB, error) {
     // time; everyone else will have to block on the connection availability.
     db.SetMaxOpenConns(1)
 
-    // Make sure to eventually close all idle connections in the pool so that
-    // SQLite actually commits its WAL journal. 
-    db.SetConnMaxIdleTime(1 * time.Minute)
-
     if (!accessible) {
         err := func () error {
             atx, err := createTransaction(db)
@@ -176,11 +172,6 @@ func initializeReadOnlyDatabase(path string) (*sql.DB, error) {
     if err != nil {
         return nil, fmt.Errorf("failed to open read-only SQLite handle; %w", err)
     }
-
-    // Make sure to eventually close all idle connections in the pool so that
-    // SQLite actually commits its WAL journal. 
-    ro_db.SetConnMaxIdleTime(1 * time.Minute)
-
     return ro_db, nil
 }
 

main.go

@@ -16,6 +16,7 @@ func main() {
     timeout0 := flag.Int("finish", 30, "Maximum time spent polling for the verification code when finishing (de)registration, in seconds")
     prefix0 := flag.String("prefix", "", "Prefix to add to each endpoint, after removing any leading or trailing slashes (default \"\")")
     lifetime0 := flag.Int("session", 10, "Maximum lifetime of a (de)registration session from start to finish, in minutes")
+    checkpoint0 := flag.Int("checkpoint", 60, "Frequency of checkpoints to synchronise the WAL journal with the SQLite file, in minutes")
     flag.Parse()
 
     dbpath := *dbpath0
@@ -66,6 +67,19 @@ func main() {
 
     http.HandleFunc(prefix + "/", newDefaultHandler())
 
+    // Adding an hourly job that does a full checkpoint.
+    {
+        lifetime := time.Duration(*checkpoint0) * time.Minute
+        ticker := time.NewTicker(lifetime)
+        defer ticker.Stop()
+        go func() {
+            for {
+                <-ticker.C
+                db.Exec("PRAGMA wal_checkpoint(PASSIVE)")
+            }
+        }()
+    }
+
     // Adding a hour job that purges various old verification sessions.
     {
         lifetime := time.Duration(*lifetime0) * time.Minute