page_cache_* session settings

These settings are available in system.settings and are autogenerated from source.

page_cache_block_size

Size of file chunks to store in the userspace page cache, in bytes. All reads that go through the cache will be rounded up to a multiple of this size.

This setting can be adjusted on a per-query level basis, but cache entries with different block sizes cannot be reused. Changing this setting effectively invalidates existing entries in the cache.

A higher value, like 1 MiB is good for high-throughput queries, and a lower value, like 64 KiB is good for low-latency point queries.

page_cache_inject_eviction

Userspace page cache will sometimes invalidate some pages at random. Intended for testing.

page_cache_lookahead_blocks

On userspace page cache miss, read up to this many consecutive blocks at once from the underlying storage, if they’re also not in the cache. Each block is page_cache_block_size bytes.

A higher value is good for high-throughput queries, while low-latency point queries will work better without readahead.

page_cache_max_coalesced_bytes

When readBigAt populates the userspace page cache, consecutive cache misses are coalesced into a single read from the underlying storage. This setting bounds the size of one coalesced read in bytes; longer miss runs are split into multiple reads. It limits transient memory usage of the temporary buffer under parallel cold reads.

A higher value reduces the number of HTTP requests for cold scans on object storage; a lower value reduces peak transient memory.