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## Problem When the utilization API was added, it was just a stub with disk space information. Disk space information isn't a very good metric for assigning tenants to pageservers, because pageservers making full use of their disks would always just have 85% utilization, irrespective of how much pressure they had for disk space. ## Summary of changes - Use the new layer visibiilty metric to calculate a "wanted size" per tenant, and sum these to get a total local disk space wanted per pageserver. This acts as the primary signal for utilization. - Also use the shard count to calculate a utilization score, and take the max of this and the disk-driven utilization. The shard count limit is currently set as a constant 20,000, which matches contemporary operational practices when loading pageservers. The shard count limit means that for tiny/empty tenants, on a machine with 3.84TB disk, each tiny tenant influences the utilization score as if it had size 160MB.
71 lines
2.2 KiB
Rust
71 lines
2.2 KiB
Rust
//! An utilization metric which is used to decide on which pageserver to put next tenant.
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//!
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//! The metric is exposed via `GET /v1/utilization`. Refer and maintain it's openapi spec as the
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//! truth.
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use anyhow::Context;
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use std::path::Path;
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use utils::serde_percent::Percent;
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use pageserver_api::models::PageserverUtilization;
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use crate::{config::PageServerConf, tenant::mgr::TenantManager};
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pub(crate) fn regenerate(
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conf: &PageServerConf,
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tenants_path: &Path,
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tenant_manager: &TenantManager,
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) -> anyhow::Result<PageserverUtilization> {
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let statvfs = nix::sys::statvfs::statvfs(tenants_path)
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.map_err(std::io::Error::from)
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.context("statvfs tenants directory")?;
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// https://unix.stackexchange.com/a/703650
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let blocksz = if statvfs.fragment_size() > 0 {
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statvfs.fragment_size()
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} else {
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statvfs.block_size()
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};
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#[cfg_attr(not(target_os = "macos"), allow(clippy::unnecessary_cast))]
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let free = statvfs.blocks_available() as u64 * blocksz;
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#[cfg_attr(not(target_os = "macos"), allow(clippy::unnecessary_cast))]
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let used = statvfs
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.blocks()
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// use blocks_free instead of available here to match df in case someone compares
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.saturating_sub(statvfs.blocks_free()) as u64
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* blocksz;
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let captured_at = std::time::SystemTime::now();
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// Calculate aggregate utilization from tenants on this pageserver
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let (disk_wanted_bytes, shard_count) = tenant_manager.calculate_utilization()?;
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// Fetch the fraction of disk space which may be used
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let disk_usable_pct = match conf.disk_usage_based_eviction.clone() {
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Some(e) => e.max_usage_pct,
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None => Percent::new(100).unwrap(),
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};
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// Express a static value for how many shards we may schedule on one node
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const MAX_SHARDS: u32 = 20000;
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let mut doc = PageserverUtilization {
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disk_usage_bytes: used,
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free_space_bytes: free,
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disk_wanted_bytes,
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disk_usable_pct,
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shard_count,
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max_shard_count: MAX_SHARDS,
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utilization_score: 0,
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captured_at: utils::serde_system_time::SystemTime(captured_at),
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};
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doc.refresh_score();
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// TODO: make utilization_score into a metric
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Ok(doc)
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}
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