v.24.7Improvement

Disable Filesystem Cache Background Download by Default

Official CH changelog text
Disable filesystem cache background download by default. It will be enabled back when we fix the issue with possible "Memory limit exceeded" because memory deallocation is done outside of query context (while buffer is allocated inside of query context) if we use background download threads. Plus we need to add a separate setting to define max size to download for background workers (currently it is limited by max_file_segment_size, which might be too big). #65534 (Kseniia Sumarokova).
Disabled filesystem cache background download by default to prevent potential "Memory limit exceeded" errors caused by memory deallocation occurring outside of the query context.

Why it matters

The feature addresses an issue where background download threads for the filesystem cache could lead to memory limit exceptions because memory deallocation happens outside the query context, while buffer allocation happens inside it. Disabling background download by default improves stability and prevents these memory issues until a fix is implemented. Additionally, there is a plan to introduce a separate setting to limit the maximum download size for background workers, since the current limit (max_file_segment_size) may be too large.

How to use it

Background download for the filesystem cache is disabled by default in this version. Once the issue is resolved and new configuration options are introduced, users will be able to enable background downloads and configure a maximum size limit for background workers through dedicated settings.

Related resources

PreviousNext