Server Settings

The maximum length of the verification chain. Verification will fail if the certificate chain length exceeds the set value.

## openSSL.server.verificationMode[​](#openssl.server.verificationmode "Direct link to openSSL.server.verificationMode")

The method for checking the node's certificates. Details are in the description of the [Context](https://github.com/ClickHouse/poco/blob/master/NetSSL_OpenSSL/include/Poco/Net/Context.h) class. Possible values: `<none>`, `<relaxed>`, `<strict>`, `<once>`.

## opentelemetry\_span\_log[​](#opentelemetry_span_log "Direct link to opentelemetry_span_log")

Settings for the [`opentelemetry_span_log`](/docs/operations/system-tables/opentelemetry_span_log) system table.

The following settings can be configured by sub-tags:

|  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
| --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- |
| Setting Description Default Note|  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | | `database` Name of the database. |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | | `table` Name of the system table. |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | | `engine` [MergeTree Engine Definition](/docs/engines/table-engines/mergetree-family/mergetree#table_engine-mergetree-creating-a-table) for a system table. Cannot be used if `partition_by` or `order_by` defined. If not specified `MergeTree` is selected by default| `partition_by` [Custom partitioning key](/docs/engines/table-engines/mergetree-family/custom-partitioning-key) for a system table. If `engine` is specified for system table, `partition_by` parameter should be specified directly inside 'engine'| `ttl` Specifies the table [TTL](/docs/engines/table-engines/mergetree-family/mergetree#table_engine-mergetree-ttl). If `engine` is specified for system table, `ttl` parameter should be specified directly inside 'engine'| `order_by` [Custom sorting key](/docs/engines/table-engines/mergetree-family/mergetree#order_by) for a system table. Can't be used if `engine` defined. If `engine` is specified for system table, `order_by` parameter should be specified directly inside 'engine'| `storage_policy` Name of the storage policy to use for the table (optional). If `engine` is specified for system table, `storage_policy` parameter should be specified directly inside 'engine'| `settings` [Additional parameters](/docs/engines/table-engines/mergetree-family/mergetree#settings) that control the behavior of the MergeTree (optional). If `engine` is specified for system table, `settings` parameter should be specified directly inside 'engine'| `flush_interval_milliseconds` Interval for flushing data from the buffer in memory to the table. `7500` |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | | `max_size_rows` Maximal size in lines for the logs. When the amount of non-flushed logs reaches the max\_size, logs are dumped to the disk. `1048576` |  |  |  |  |  |  |  |  |  |  |  |  | | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | | `reserved_size_rows` Pre-allocated memory size in lines for the logs. `8192` |  |  |  |  |  |  |  |  | | --- | --- | --- | --- | --- | --- | --- | --- | | `buffer_size_rows_flush_threshold` Threshold for amount of lines. If the threshold is reached, flushing logs to the disk is launched in background. `max_size_rows / 2` |  |  |  |  | | --- | --- | --- | --- | | `flush_on_crash` Sets whether logs should be dumped to the disk in case of a crash. `false`  | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | |

Example:

```
<opentelemetry_span_log>
    <engine>
        engine MergeTree
        partition by toYYYYMM(finish_date)
        order by (finish_date, finish_time_us, trace_id)
    </engine>
    <database>system</database>
    <table>opentelemetry_span_log</table>
    <flush_interval_milliseconds>7500</flush_interval_milliseconds>
    <max_size_rows>1048576</max_size_rows>
    <reserved_size_rows>8192</reserved_size_rows>
    <buffer_size_rows_flush_threshold>524288</buffer_size_rows_flush_threshold>
    <flush_on_crash>false</flush_on_crash>
</opentelemetry_span_log>
```

## os\_collect\_psi\_metrics[​](#os_collect_psi_metrics "Direct link to os_collect_psi_metrics")

Enable accounting PSI metrics from /proc/pressure/ files.

## os\_cpu\_busy\_time\_threshold[​](#os_cpu_busy_time_threshold "Direct link to os_cpu_busy_time_threshold")

Threshold of OS CPU busy time in microseconds (OSCPUVirtualTimeMicroseconds metric) to consider CPU doing some useful work, no CPU overload would be considered if busy time was below this value.

## os\_threads\_nice\_value\_distributed\_cache\_tcp\_handler[​](#os_threads_nice_value_distributed_cache_tcp_handler "Direct link to os_threads_nice_value_distributed_cache_tcp_handler")

Linux nice value for the threads of distributed cache TCP handler. Lower values mean higher CPU priority.

Requires CAP\_SYS\_NICE capability, otherwise no-op.

Possible values: -20 to 19.

## os\_threads\_nice\_value\_merge\_mutate[​](#os_threads_nice_value_merge_mutate "Direct link to os_threads_nice_value_merge_mutate")

Linux nice value for merge and mutation threads. Lower values mean higher CPU priority.

Requires CAP\_SYS\_NICE capability, otherwise no-op.

Possible values: -20 to 19.

## os\_threads\_nice\_value\_zookeeper\_client\_send\_receive[​](#os_threads_nice_value_zookeeper_client_send_receive "Direct link to os_threads_nice_value_zookeeper_client_send_receive")

Linux nice value for send and receive threads in ZooKeeper client. Lower values mean higher CPU priority.

Requires CAP\_SYS\_NICE capability, otherwise no-op.

Possible values: -20 to 19.

## page\_cache\_free\_memory\_ratio[​](#page_cache_free_memory_ratio "Direct link to page_cache_free_memory_ratio")

Fraction of the memory limit to keep free from the userspace page cache. Analogous to Linux min\_free\_kbytes setting.

## page\_cache\_history\_window\_ms[​](#page_cache_history_window_ms "Direct link to page_cache_history_window_ms")

Delay before freed memory can be used by userspace page cache.

## page\_cache\_max\_size[​](#page_cache_max_size "Direct link to page_cache_max_size")

Maximum size of the userspace page cache. Set to 0 to disable the cache. If greater than page\_cache\_min\_size, the cache size will be continuously adjusted within this range, to use most of the available memory while keeping the total memory usage below the limit (max\_server\_memory\_usage[\_to\_ram\_ratio]).