kvdb/sqlite: enable incremental auto_vacuum on DB creation

In this commit, we make a change that enables the `auto_vacuum =
incremental` pragma for SQLite databases, but only when the database
file is first created. Incremental auto-vacuum allows SQLite to reclaim
unused space within the database file over time, preventing indefinite
growth.

According to the SQLite documentation, the `auto_vacuum` mode must be
set *before* any tables are created in the database. To achieve this, a
new boolean parameter `isCreate` has been added to the
`NewSqliteBackend` function.

The `createDBDriver` now passes `true` for this parameter, ensuring the
pragma is set during initial database setup. Conversely, `openDBDriver`
passes `false` when opening an existing database, leaving the existing
vacuum mode untouched.

We also, the internal representation of pragma options was refactored to
use a named struct `pragmaOption` for improved clarity.

Author: Roasbeef

kvdb/sqlite/db.go

@@ -24,17 +24,21 @@ const (
 	sqliteTxLockImmediate = "_txlock=immediate"
 )
 
+// pragmaOption holds a key-value pair for a SQLite pragma setting.
+type pragmaOption struct {
+	name  string
+	value string
+}
+
 // NewSqliteBackend returns a db object initialized with the passed backend
 // config. If a sqlite connection cannot be established, then an error is
 // returned.
 func NewSqliteBackend(ctx context.Context, cfg *Config, dbPath, fileName,
-	prefix string) (walletdb.DB, error) {
+	prefix string, isCreate bool) (walletdb.DB, error) {
 
 	// First, we add a set of mandatory pragma options to the query.
-	pragmaOptions := []struct {
-		name  string
-		value string
-	}{
+	// Use the new named struct pragmaOption.
+	pragmaOptions := []pragmaOption{
 		{
 			name: "busy_timeout",
 			value: fmt.Sprintf(
@@ -50,6 +54,18 @@ func NewSqliteBackend(ctx context.Context, cfg *Config, dbPath, fileName,
 			value: "WAL",
 		},
 	}
+
+	// If the database is being created, set auto_vacuum to incremental.
+	// This must be done before any tables are created. According to the
+	// SQLite docs, this corresponds to mode 2.
+	if isCreate {
+		// Use the new named struct pragmaOption here as well.
+		pragmaOptions = append(pragmaOptions, pragmaOption{
+			name:  "auto_vacuum",
+			value: "incremental",
+		})
+	}
+
 	sqliteOptions := make(url.Values)
 	for _, option := range pragmaOptions {
 		sqliteOptions.Add(

kvdb/sqlite/driver.go

@@ -5,6 +5,8 @@ package sqlite
 import (
 	"context"
 	"fmt"
+	"os"
+	"path/filepath"
 
 	"github.com/btcsuite/btcwallet/walletdb"
 )
@@ -69,7 +71,8 @@ func createDBDriver(args ...interface{}) (walletdb.DB, error) {
 		return nil, err
 	}
 
-	return NewSqliteBackend(ctx, config, dbPath, filename, prefix)
+	// Pass 'true' for isCreate when creating the database via walletdb.Create.
+	return NewSqliteBackend(ctx, config, dbPath, filename, prefix, true)
 }
 
 // openDBDriver is the callback provided during driver registration that opens
@@ -80,7 +83,29 @@ func openDBDriver(args ...interface{}) (walletdb.DB, error) {
 		return nil, err
 	}
 
-	return NewSqliteBackend(ctx, config, dbPath, filename, prefix)
+	// Check if the database file already exists. The walletdb.Open function
+	// is meant to open existing databases, but the underlying driver might
+	// create one if it doesn't exist. We need to know if we are creating
+	// it here to set the initial pragmas correctly (like auto_vacuum).
+	fullPath := filepath.Join(dbPath, filename)
+	_, err = os.Stat(fullPath)
+	isCreate := false
+	if err != nil {
+		// If the error is specifically that the file doesn't exist,
+		// then we are effectively creating it now.
+		if os.IsNotExist(err) {
+			isCreate = true
+		} else {
+			// For any other error (e.g., permission issues),
+			// return the error.
+			return nil, fmt.Errorf("error checking db file "+
+				"%s: %w", fullPath, err)
+		}
+	}
+
+	// Pass the determined isCreate flag to NewSqliteBackend.
+	// It will be true only if os.Stat reported IsNotExist.
+	return NewSqliteBackend(ctx, config, dbPath, filename, prefix, isCreate)
 }
 
 func init() {