---
title: Systemic object marking
---

In Deephaven, a **systemic object** is an object whose failure causes Deephaven to terminate the entire worker process. When systemic object marking is disabled (the default), all objects are treated as systemic and any object failure is fatal. When marking is enabled, threads are non-systemic by default — only objects created on explicitly marked threads or within a scoped execution are systemic. This guide explains how to control this behavior using the [`deephaven.systemic_obj_tracker`](https://docs.deephaven.io/core/pydoc/code/deephaven.systemic_obj_tracker.html) module.

## Enable systemic object marking

Systemic object marking is not user-configurable at runtime by default. To enable this feature, start the server with the JVM option:

```
-DSystemicObjectTracker.enabled=true
```

Check if systemic object marking is enabled:

```python test-set=1 order=null
from deephaven.systemic_obj_tracker import is_systemic_object_marking_enabled

print(is_systemic_object_marking_enabled())
```

## Manage thread systemic status

Systemic object creation is controlled per thread. When systemic object marking is enabled, you can programmatically set a thread as systemic or non-systemic at runtime. While a thread is systemic, any object it creates is also systemic; when non-systemic, objects are not marked as systemic.

Check and toggle the systemic status of the current thread:

```python test-set=1 order=null
from deephaven.systemic_obj_tracker import is_systemic, set_systemic

if is_systemic_object_marking_enabled():
    set_systemic(not is_systemic())
else:
    print("Systemic object marking is not currently enabled.")
```

## Context managers

The [`deephaven.systemic_obj_tracker`](https://docs.deephaven.io/core/pydoc/code/deephaven.systemic_obj_tracker.html) module provides context managers to enable or disable systemic object creation within code blocks.

```python skip-test
from deephaven import empty_table
from deephaven.systemic_obj_tracker import (
    systemic_object_marking,
    no_systemic_object_marking,
)

# Create a systemic table
with systemic_object_marking():
    systemic_t = empty_table(1).update("Label=`I am systemic`")

# Create a non-systemic table
with no_systemic_object_marking():
    not_systemic_t = empty_table(1).update("Label=`I am not systemic`")
```

## Systemic scripts from the Python Client

When executing a script on the server from the Python client, you can control whether objects created by that script are marked as systemic by using the `systemic` argument—provided systemic object marking is enabled on the server. If systemic object marking is disabled on the server, the `systemic` argument has no effect, and all objects created by the script will be systemic by default.

```python skip-test
from pydeephaven import Session

# Deephaven server running on <localhost:10000> with 'Anonymous' authentication
session = Session()

critical_script = """
from deephaven import empty_table

t = empty_table(1).update("Label=`I am systemic`")
"""
session.run_script(critical_script, systemic=True)
```

## Related documentation

- [Server Pydoc](https://docs.deephaven.io/core/pydoc/code/deephaven.systemic_obj_tracker.html)
- [Client Pydoc](https://docs.deephaven.io/core/client-api/python/code/pydeephaven.html#pydeephaven.Session.run_script)