> ## 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.

# max_prefixes_* server settings

> ClickHouse server settings in the max_prefixes_* generated group.

These settings configure the ClickHouse server and are autogenerated from ClickHouse source.

## max\_prefixes\_deserialization\_thread\_pool\_free\_size

Type

UInt64

Default

0

Changeable without restart

Yes

If the number of **idle** threads in the prefixes deserialization Thread pool exceeds `max_prefixes_deserialization_thread_pool_free_size`, ClickHouse will release resources occupied by idling threads and decrease the pool size. Threads can be created again if necessary.

## max\_prefixes\_deserialization\_thread\_pool\_size

Type

UInt64

Default

100

Changeable without restart

Yes

ClickHouse uses threads from the prefixes deserialization Thread pool for parallel reading of metadata of columns and subcolumns from file prefixes in Wide parts in MergeTree. `max_prefixes_deserialization_thread_pool_size` limits the maximum number of threads in the pool.