Use writeWithoutTransaction when appropriate (#53)

This pull request fixes SQLITE_BUSY errors caused by the shift to IMMEDIATE transactions.

Updating the transaction type https://sqlite.org/lang_transaction.html#deferred_immediate_and_exclusive_transactions from the default DEFERRED to IMMEDIATE exposed some issues with the way SQLite wrapped GRDB. SQLite was wrapping some writes in an unnecessary transaction. This caused issues because IMMEDIATE transactions immediately begin a write, meaning other writes will receive a SQLITE_BUSY error. Before applying the changes in this pull request, vacuuming and checkpointing tests failed when IMMEDIATE transactions were used.

Author: atdrendel

.github/workflows/ci.yml

@@ -5,10 +5,11 @@ on: push
 jobs:
   test:
     runs-on: macos-13
-    
+
     steps:
       - uses: actions/checkout@v3
       - name: Select Xcode 15
         run: sudo xcode-select -s /Applications/Xcode_15.0.app
       - name: Test
         run: swift test
+

Sources/SQLite/SQLiteDatabase.swift

@@ -111,6 +111,20 @@ public final class SQLiteDatabase: DatabaseProtocol, @unchecked Sendable {
         )
     }
 
+    public func truncate() throws {
+        switch database {
+        case let .pool(pool):
+            try pool.writeWithoutTransaction { db in
+                _ = try db.execute(raw: "PRAGMA wal_checkpoint(TRUNCATE);")
+            }
+
+        case let .queue(queue):
+            try queue.writeWithoutTransaction { db in
+                _ = try db.execute(raw: "PRAGMA wal_checkpoint(TRUNCATE);")
+            }
+        }
+    }
+
     // NOTE: This function is only really meant to be called in tests.
     public func close() throws {
         changeNotifier.stop()
@@ -275,7 +289,7 @@ public extension SQLiteDatabase {
     @discardableResult
     func execute(raw sql: SQL) async throws -> [SQLiteRow] {
         do {
-            return try await database.writer.write { db in
+            return try await database.writer.writeWithoutTransaction { db in
                 try db.execute(raw: sql)
             }
         } catch {
@@ -339,7 +353,7 @@ public extension SQLiteDatabase {
     @discardableResult
     func execute(raw sql: SQL) throws -> [SQLiteRow] {
         do {
-            return try database.writer.write { db in
+            return try database.writer.writeWithoutTransaction { db in
                 try db.execute(raw: sql)
             }
         } catch {
@@ -644,13 +658,10 @@ private extension SQLiteDatabase {
         config.journalMode = isInMemory ? .default : .wal
         // NOTE: GRDB recommends `defaultTransactionKind` be set
         //       to `.immediate` in order to prevent `SQLITE_BUSY`
-        //       errors. Using `.immediate` appears to disable
-        //       automatic vacuuming.
+        //       errors.
         //
         // https://swiftpackageindex.com/groue/grdb.swift/v6.24.2/documentation/grdb/databasesharing#How-to-limit-the-SQLITEBUSY-error
-        config.defaultTransactionKind = isInMemory
-            ? .deferred
-            : .immediate
+        config.defaultTransactionKind = .immediate
         config.busyMode = .timeout(busyTimeout)
         config.observesSuspensionNotifications = true
         config.maximumReaderCount = max(
@@ -770,7 +781,7 @@ private enum Database {
         arguments: SQLiteArguments = [:]
     ) throws {
         do {
-            try writer.write { db in
+            try writer.writeWithoutTransaction { db in
                 try db.write(sql, arguments: arguments)
             }
         } catch {

Tests/SQLiteTests/SQLiteDatabaseTests.swift

@@ -253,6 +253,27 @@ final class SQLiteDatabaseTests: XCTestCase {
         }
     }
 
+    func testCheckpointUsingTruncate() throws {
+        try Sandbox.execute { directory in
+            let path = directory.appendingPathComponent("test.db").path
+            let db = try SQLiteDatabase(path: path)
+            defer { try? db.close() }
+
+            try db.execute(raw: _createTableWithBlob)
+
+            try db.inTransaction { db in
+                for index in 0 ..< 100 {
+                    let args: SQLiteArguments = [
+                        "id": .integer(Int64(index)), "data": .data(_textData),
+                    ]
+                    try db.write(_insertIDAndData, arguments: args)
+                }
+            }
+
+            try db.truncate()
+        }
+    }
+
     func testCreateTable() throws {
         XCTAssertNoThrow(try database.execute(raw: _createTableWithBlob))
         let tableNames = try database.tables()