backend/database/database.go

@@ -54,9 +54,19 @@ type DB struct {
 // form is silently ignored, which is why WAL was never actually on.
 const (
 	writeDSNParams = "?_pragma=busy_timeout(5000)&_pragma=journal_mode(WAL)"
-	readDSNParams  = "?_pragma=busy_timeout(5000)&_pragma=journal_mode(WAL)" +
+	// The read pool's own page cache and mapping bound, sized by
+	// measurement rather than by appetite (#283).  On a 50 000-track
+	// library, halving the cache and quartering the mapping moved no
+	// query — 1 172 → 1 197 ms for the whole track list, 106 → 124 ms
+	// for the album list, 6 → 8 ms for an FTS search, all inside the
+	// run-to-run spread — and the RSS of the database mapping was 46 MB
+	// under both settings, because a mapping's cost is what the working
+	// set touches, not the bound.  The bound is what matters on a
+	// phone, where five connections' worth of address space is the
+	// thing the low-memory killer reads (cf. #52).
+	readDSNParams = "?_pragma=busy_timeout(5000)&_pragma=journal_mode(WAL)" +
 		"&_pragma=query_only(true)&_pragma=synchronous(NORMAL)" +
-		"&_pragma=cache_size(-8000)&_pragma=mmap_size(67108864)"
+		"&_pragma=cache_size(-2000)&_pragma=mmap_size(16777216)"
 	// readPoolConns bounds concurrent read connections.  A handful is
 	// plenty for interactive search + art/lookup fan-out and keeps WAL
 	// reader overhead small.
@@ -354,8 +364,8 @@ func applyPRAGMAs(ctx context.Context, db *sql.DB) error {
 	pragmas := []string{
 		"PRAGMA foreign_keys = ON",
 		"PRAGMA synchronous = NORMAL",
-		"PRAGMA cache_size = -8000",
-		"PRAGMA mmap_size = 67108864",
+		"PRAGMA cache_size = -2000",
+		"PRAGMA mmap_size = 16777216",
 	}
 
 	for _, pragma := range pragmas {