rust/neon
1
0
Fork 0
mirror of https://github.com/neondatabase/neon.git synced 2026-05-18 21:50:37 +00:00
Code Issues Packages Projects Releases Wiki Activity

doc: more explanation of the added config knobs

Browse Source
This commit is contained in:
Christian Schwarz
2023-03-27 19:52:48 +02:00
parent ef39b3f067
commit 0462563d31
2 changed files with 19 additions and 4 deletions
Download Patch File Download Diff File Expand all files Collapse all files

4
pageserver/src/config.rs
View File

@@ -93,6 +93,8 @@ pub mod defaults {
#evictions_low_residence_duration_metric_threshold = '{DEFAULT_EVICTIONS_LOW_RESIDENCE_DURATION_METRIC_THRESHOLD}'
#disk_usage_based_eviction = {{ max_usage_pct = .., min_avail_bytes = .., period = "10s"}}
# [tenant_config]
#checkpoint_distance = {DEFAULT_CHECKPOINT_DISTANCE} # in bytes
#checkpoint_timeout = {DEFAULT_CHECKPOINT_TIMEOUT}
@@ -105,6 +107,8 @@ pub mod defaults {
#image_creation_threshold = {DEFAULT_IMAGE_CREATION_THRESHOLD}
#pitr_interval = '{DEFAULT_PITR_INTERVAL}'
#min_resident_size_override = .. # in bytes
# [remote_storage]
"###

19
pageserver/src/disk_usage_eviction_task.rs
View File

@@ -19,10 +19,21 @@
//! `min_avail_bytes` is the absolute available space in bytes.
//! If the actual usage is lower, the threshold is exceeded.
//!
//! The iteration evicts layers in LRU fashion.
//! It tries first with a reservation of up to `tenant_min_resident_size` bytes of the most recent layers per tenant.
//! The layers not part of the per-tenant reservation are evicted least-recently-used first until we're below all thresholds.
//! If the per-tenant-reservation strategy doesn't work out, it falls back to global LRU.
//! The iteration evicts layers in LRU fashion, but, with a weak reservation per tenant.
//! The reservation is to keep the most recently accessed X bytes per tenant resident.
//! All layers that don't make the cut are put on a list and become eviction candidates.
//! We evict until we're below the two thresholds.
//!
//! If the above strategy wouldn't free enough space, we fall back to global LRU right away,
//! not respecting any per-tenant reservations.
//!
//! This value for the per-tenant reservation is referred to as `tenant_min_resident_size`
//! throughout the code, but, no actual variable carries that name.
//! The per-tenant default value is the `max(tenant's layer file sizes, regardless of local or remote)`.
//! The idea is to allow at least one layer to be resident per tenant, to ensure it can make forward progress
//! during page reconstruction.
//! An alternative default for all tenants can be specified in the `tenant_config` section of the config.
//! Lastly, each tenant can have an override in their respectice tenant config (`min_resident_size_override`).
// Implementation notes:
// - The `#[allow(dead_code)]` above various structs are to suppress warnings about only the Debug impl