add transaction begin types

src/network/cache/SqliteCache.zig

@@ -126,7 +126,7 @@ pub fn get(self: *SqliteCache, arena: std.mem.Allocator, req: CacheRequest) !?Ca
     const conn = try self.pool.acquire();
     defer self.pool.release(conn);
 
-    try conn.begin();
+    try conn.begin(.immediate);
     defer conn.rollback() catch {};
 
     var entry = try conn.row(
@@ -252,7 +252,7 @@ pub fn put(self: *SqliteCache, meta: CachedMetadata, body: []const u8) !void {
     const conn = try self.pool.acquire();
     defer self.pool.release(conn);
 
-    try conn.begin();
+    try conn.begin(.immediate);
     defer conn.rollback() catch {};
 
     try conn.exec("delete from metadata where url = $1", .{meta.url});
@@ -327,7 +327,7 @@ pub fn renew(self: *SqliteCache, _: std.mem.Allocator, req: RenewResponse) !void
     const conn = try self.pool.acquire();
     defer self.pool.release(conn);
 
-    try conn.begin();
+    try conn.begin(.immediate);
     defer conn.rollback() catch {};
 
     const exists = try conn.row("select 1 from metadata where url = $1", .{req.url});

src/storage/sqlite/Sqlite.zig

@@ -65,7 +65,7 @@ pub const Migrations = struct {
             return start;
         }
 
-        try conn.begin();
+        try conn.begin(.immediate);
         errdefer conn.rollback() catch {};
 
         for (migrations[start..], start..) |migration, i| {
@@ -168,8 +168,13 @@ pub const Conn = struct {
         return .{ .stmt = stmt.?, .conn = self.conn };
     }
 
-    pub fn begin(self: Conn) !void {
-        try self.exec("begin", .{});
+    pub const BeginKind = enum { deferred, immediate, exclusive };
+    pub fn begin(self: Conn, kind: BeginKind) !void {
+        switch (kind) {
+            .deferred => try self.exec("begin deferred", .{}),
+            .immediate => try self.exec("begin immediate", .{}),
+            .exclusive => try self.exec("begin exclusive", .{}),
+        }
     }
 
     pub fn commit(self: Conn) !void {