> ## Documentation Index
> Fetch the complete documentation index at: https://clickhouse.com/docs/llms.txt
> Use this file to discover all available pages before exploring further.

# system_* session settings

> ClickHouse session settings in the system_* generated group.

export const SettingsInfoBlock = ({type, default_value, changeable_without_restart}) => {
  return <div className="not-prose" style={{
    display: "flex",
    flexWrap: "wrap",
    alignItems: "baseline",
    columnGap: "0.5rem",
    rowGap: "0.125rem",
    margin: "0.375rem 0",
    fontSize: "0.8125rem",
    lineHeight: "1.125rem"
  }}>
      <div style={{
    fontWeight: 600,
    opacity: 0.72
  }}>Type</div>
      <div style={{
    overflowWrap: "anywhere"
  }}>{type}</div>
      <div style={{
    fontWeight: 600,
    opacity: 0.72,
    marginInlineStart: "0.5rem"
  }}>Default</div>
      <div style={{
    overflowWrap: "anywhere"
  }}>{default_value}</div>
      {changeable_without_restart && <div style={{
    fontWeight: 600,
    opacity: 0.72,
    marginInlineStart: "0.5rem"
  }}>
          Changeable without restart
        </div>}
      {changeable_without_restart && <div style={{
    overflowWrap: "anywhere"
  }}>
          {changeable_without_restart}
        </div>}
    </div>;
};

These settings are available in [system.settings](/docs/reference/system-tables/settings) and are autogenerated from [source](https://github.com/ClickHouse/ClickHouse/blob/master/src/Core/Settings.cpp).

<h2 id="system_events_show_zero_values">
  system\_events\_show\_zero\_values
</h2>

<SettingsInfoBlock type="Bool" default_value="0" />

Allows to select zero-valued events from [`system.events`](/docs/reference/system-tables/events).

Some monitoring systems require passing all the metrics values to them for each checkpoint, even if the metric value is zero.

Possible values:

* 0 — Disabled.
* 1 — Enabled.

**Examples**

Query

```sql theme={null}
SELECT * FROM system.events WHERE event='QueryMemoryLimitExceeded';
```

Result

```text theme={null}
Ok.
```

Query

```sql theme={null}
SET system_events_show_zero_values = 1;
SELECT * FROM system.events WHERE event='QueryMemoryLimitExceeded';
```

Result

```text theme={null}
┌─event────────────────────┬─value─┬─description───────────────────────────────────────────┐
│ QueryMemoryLimitExceeded │     0 │ Number of times when memory limit exceeded for query. │
└──────────────────────────┴───────┴───────────────────────────────────────────────────────┘
```

<h2 id="system_metric_log_show_zero_values_in_histograms">
  system\_metric\_log\_show\_zero\_values\_in\_histograms
</h2>

<SettingsInfoBlock type="Bool" default_value="0" />

<VersionHistory rows={[{"id": "row-1","items": [{"label": "26.5"},{"label": "0"},{"label": "New setting controlling whether zero-valued histogram data is written to the histograms nested column of system.metric_log."}]}]} />

Controls whether zero-valued histogram data is written to the `histograms` nested column of `system.metric_log`.

By default, histograms whose total observation `count` is zero are skipped, and within each emitted histogram, bucket entries with no observations are also omitted from the `histogram` map. Enable this to write every histogram and every bucket regardless of count — useful for monitoring systems that require every metric to appear at every checkpoint.

Possible values:

* 0 — Disabled. Histograms with `count = 0` are not emitted; emitted histograms include only buckets that received at least one observation.
* 1 — Enabled. All histograms are written, and every bucket boundary appears in `histogram`.