---
title: Configuration
sidebar_position: 4
id: configuration
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  Licensed to the Apache Software Foundation (ASF) under one or more
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  this work for additional information regarding copyright ownership.
  The ASF licenses this file to You under the Apache License, Version 2.0
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---

This page covers C++ Fory instance configuration. `Fory::builder()` creates xlang
payloads by default. Compatible mode is also enabled by default. Select native
mode only when the payload stays in C++.

## Builder Pattern

Use `Fory::builder()` to construct Fory instances with custom configuration:

```cpp
#include "fory/serialization/fory.h"

using namespace fory::serialization;

// Default xlang mode.
auto fory = Fory::builder().build();

// Native mode for C++-only payloads.
auto fory = Fory::builder()
    .xlang(false)
    .build();

// Same-schema optimization. Use only when every reader and writer
// always uses the same schema.
auto fory = Fory::builder()
    .compatible(false)
    .build();
```

## Configuration

### xlang(bool)

Select the wire mode.

```cpp
auto fory = Fory::builder()
    .xlang(false)
    .build();
```

When `true`, C++ writes the xlang wire format used by Java, Python, Go, Rust,
JavaScript/TypeScript, C#, Swift, Dart, Scala, and Kotlin. When `false`, C++
writes native-mode payloads for C++-only traffic.

**Default:** `true`

### compatible(bool)

Compatible mode is enabled by default. No builder call is required for the
default compatible mode. Set `.compatible(false)` only when every reader and
writer always uses the same schema and you want faster serialization and smaller
size.

```cpp
auto fory = Fory::builder()
    .compatible(false)
    .build();
```

For xlang payloads, use `.compatible(false)` only after verifying that every language uses the same schema, or when native types are generated from Fory schema IDL.

**Default:** `true`

### track_ref(bool)

Enable/disable reference tracking for shared and circular references.

```cpp
auto fory = Fory::builder()
    .track_ref(true)  // Enable reference tracking
    .build();
```

When enabled, avoids duplicating shared objects and handles cycles.

**Default:** `true`

### max_graph_memory_bytes(int64_t)

Set an approximate graph-memory gate for one root deserialization.

```cpp
auto fory = Fory::builder()
    .max_graph_memory_bytes(64 * 1024 * 1024)
    .build();
```

The default limit is a fixed `128 MiB` for byte-array, `Buffer`, and stream
roots. Positive values override the default. Explicit non-positive values are
rejected when the Fory instance is created.

This budget is an approximate lower-bound estimate for materialized graph
owners, mainly collections, maps, arrays, structs, and objects. It is not an
exact process heap limit; actual process memory can be higher. Dedicated
string, binary, primitive scalar, and primitive dense-array leaf values are
skipped by this budget and continue to rely on byte-availability checks: if the
unread input does not contain enough bytes, Fory will not read or create that
leaf value.

**Default:** `128 MiB`

### max_unbacked_container_items(int64_t)

Limit collection elements and map entries whose repeated read bodies do not
consume proportional input during one root deserialization. The default is
`8192`; zero is a strict limit.

```cpp
auto fory = Fory::builder()
    .max_unbacked_container_items(8192)
    .build();
```

### max_dyn_depth(uint32_t)

Set maximum allowed nesting depth for dynamically-typed objects.

```cpp
auto fory = Fory::builder()
    .max_dyn_depth(10)  // Allow up to 10 levels
    .build();
```

This limits the maximum depth for nested polymorphic object serialization (e.g., `shared_ptr<Base>`, `unique_ptr<Base>`). This prevents stack overflow from deeply nested structures in dynamic serialization scenarios.

**Default:** `5`

**When to adjust:**

- **Increase**: For legitimate deeply nested data structures
- **Decrease**: For stricter security requirements or shallow data structures

### max_schema_versions_per_type(uint32_t)

Set the maximum cached remote metadata versions for one logical type.

```cpp
auto fory = Fory::builder()
    .max_schema_versions_per_type(10)
    .build();
```

**Default:** `10`

Schema-version limits bound cached metadata only. When a schema-version or
logical-type cache limit is reached, valid data still deserializes after full
metadata validation, without caching the new schema. Repeated reads of an
uncached schema may cost more; existing cached schemas remain reusable.

### max_type_fields(uint32_t)

Set the maximum fields accepted in one received remote struct metadata body.

```cpp
auto fory = Fory::builder()
    .max_type_fields(512)
    .build();
```

**Default:** `512`

### max_type_meta_bytes(uint32_t)

Set the maximum encoded body bytes accepted for one received TypeDef body,
excluding the 8-byte header and any extended-size varint.

```cpp
auto fory = Fory::builder()
    .max_type_meta_bytes(4096)
    .build();
```

**Default:** `4096`

### max_average_schema_versions_per_type(uint32_t)

Set the average cached remote metadata versions across cached remote types.
The effective global floor is `8192` schemas.

```cpp
auto fory = Fory::builder()
    .max_average_schema_versions_per_type(3)
    .build();
```

**Default:** `3`

### check_struct_version(bool)

Enable/disable struct version checking.

```cpp
auto fory = Fory::builder()
    .compatible(false)
    .check_struct_version(true)  // Enable version checking
    .build();
```

When enabled, validates type hashes to detect schema mismatches.

**Default:** `false`

## Thread-Safe vs Single-Threaded

### Single-Threaded (Fastest)

```cpp
auto fory = Fory::builder().build();  // Returns Fory
```

Single-threaded `Fory` is the fastest option, but NOT thread-safe. Use one instance per thread.

### Thread-Safe

```cpp
auto fory = Fory::builder().build_thread_safe();  // Returns ThreadSafeFory
```

`ThreadSafeFory` uses a pool of Fory instances to provide thread-safe serialization. Slightly slower due to pool overhead, but safe to use from multiple threads concurrently.

## Configuration Summary

| Option                                           | Description                                              | Default   |
| ------------------------------------------------ | -------------------------------------------------------- | --------- |
| `xlang(bool)`                                    | Use xlang mode                                           | `true`    |
| `compatible(bool)`                               | Enable schema evolution                                  | `true`    |
| `track_ref(bool)`                                | Enable reference tracking                                | `true`    |
| `max_graph_memory_bytes(int64_t)`                | Approximate graph-memory gate per root read              | `128 MiB` |
| `max_unbacked_container_items(int64_t)`          | Unbacked collection/map work per root read               | `8192`    |
| `max_dyn_depth(uint32_t)`                        | Maximum nesting depth for dynamic types                  | `5`       |
| `max_type_fields(uint32_t)`                      | Max fields in one received struct metadata body          | `512`     |
| `max_type_meta_bytes(uint32_t)`                  | Max encoded bytes in one received metadata body          | `4096`    |
| `max_schema_versions_per_type(uint32_t)`         | Max cached remote metadata versions for one logical type | `10`      |
| `max_average_schema_versions_per_type(uint32_t)` | Average cached remote metadata versions across types     | `3`       |
| `check_struct_version(bool)`                     | Enable struct version checking                           | `false`   |

## Security

See [C++ Security](security.md) for trust boundaries, safe reader configuration, and verification.

## Related Topics

- [Basic Serialization](basic-serialization.md) - Using configured Fory
- [Cross-Language Interoperability](basic-serialization.md#cross-language-interoperability) - xlang mode details
- [Type Registration](type-registration.md) - Registering types