Re: [pdm-devel] [PATCH proxmox-datacenter-manager 06/25] metric collection: save metric data to RRD in separate task

[Wolfgang Bumiller <w.bumiller@proxmox.com>]

On Tue, Feb 11, 2025 at 01:05:22PM +0100, Lukas Wagner wrote:
> This is a preparation for concurrent metric collection. While the RRD
> cache appears to be safe to concurrent access (it uses an RwLock to
> protect the data), delegating all RRD writes to a separate tokio task
> makes it IMO easier to reason about and understand. Furthermore, it
> decouples the 'metric fetching' and 'metric
> storing' parts, making it much easier to write tests for both parts
> independently.
> 
> For better code separation, this also splits out the new task into
> a new submodule.
> 
> Signed-off-by: Lukas Wagner <l.wagner@proxmox.com>
> ---
>  server/src/metric_collection/mod.rs      | 102 +++++++----------------
>  server/src/metric_collection/rrd_task.rs |  92 ++++++++++++++++++++
>  2 files changed, 124 insertions(+), 70 deletions(-)
>  create mode 100644 server/src/metric_collection/rrd_task.rs
> 
> diff --git a/server/src/metric_collection/mod.rs b/server/src/metric_collection/mod.rs
> index 5540f93..06ade5f 100644
> --- a/server/src/metric_collection/mod.rs
> +++ b/server/src/metric_collection/mod.rs
> @@ -2,18 +2,18 @@ use std::collections::HashMap;
>  use std::pin::pin;
>  
>  use anyhow::Error;
> -
> -use pbs_api_types::{MetricDataPoint, MetricDataType};
> -use proxmox_rrd::rrd::DataSourceType;
> +use tokio::sync::mpsc::{self, Sender};
>  
>  use pdm_api_types::remotes::RemoteType;
> -use pve_api_types::{ClusterMetricsData, ClusterMetricsDataType};
>  
>  use crate::{connection, task_utils};
>  
>  pub mod rrd_cache;
> +mod rrd_task;
>  pub mod top_entities;
>  
> +use rrd_task::RrdStoreRequest;
> +
>  const COLLECTION_INTERVAL: u64 = 60;
>  
>  /// Initialize the RRD cache
> @@ -25,14 +25,22 @@ pub fn init() -> Result<(), Error> {
>  
>  /// Start the metric collection task.
>  pub fn start_task() {
> +    let (tx, rx) = mpsc::channel(128);
> +
> +    tokio::spawn(async move {
> +        let task_scheduler = pin!(metric_collection_task(tx));
> +        let abort_future = pin!(proxmox_daemon::shutdown_future());
> +        futures::future::select(task_scheduler, abort_future).await;
> +    });
> +
>      tokio::spawn(async move {
> -        let task_scheduler = pin!(metric_collection_task());
> +        let task_scheduler = pin!(rrd_task::store_in_rrd_task(rx));
>          let abort_future = pin!(proxmox_daemon::shutdown_future());
>          futures::future::select(task_scheduler, abort_future).await;
>      });
>  }
>  
> -async fn metric_collection_task() -> Result<(), Error> {
> +async fn metric_collection_task(sender: Sender<RrdStoreRequest>) -> Result<(), Error> {
>      let mut most_recent_timestamps: HashMap<String, i64> = HashMap::new();
>  
>      loop {
> @@ -59,37 +67,33 @@ async fn metric_collection_task() -> Result<(), Error> {
>                              .cluster_metrics_export(Some(true), Some(false), Some(start_time))
>                              .await?;
>  
> -                        //// Involves some blocking file IO
> -                        tokio::task::spawn_blocking(move || {
> -                            let mut most_recent_timestamp = 0;
> +                        let most_recent =
> +                            metrics.data.iter().fold(0, |acc, x| acc.max(x.timestamp));

Might be more readable using `Iterator::max()`:

    metrics.data.iter().map(|e| e.timestamp).max().unwrap_or(0);

(while this changes throughout the series, there's at least 1 instance
of this pattern remaining at the end AFAICT)

>  
> -                            for data_point in metrics.data {
> -                                most_recent_timestamp =
> -                                    most_recent_timestamp.max(data_point.timestamp);
> -                                store_metric_pve(&remote_name_clone, &data_point);
> -                            }
> +                        sender
> +                            .send(RrdStoreRequest::Pve {
> +                                remote: remote_name_clone,
> +                                metrics,
> +                            })
> +                            .await?;
>  
> -                            most_recent_timestamp
> -                        })
> -                        .await
> +                        Ok::<i64, Error>(most_recent)

^ This...

>                      }
>                      RemoteType::Pbs => {
>                          let client = connection::make_pbs_client(remote)?;
>                          let metrics = client.metrics(Some(true), Some(start_time)).await?;
>  
> -                        // Involves some blocking file IO
> -                        tokio::task::spawn_blocking(move || {
> -                            let mut most_recent_timestamp = 0;
> +                        let most_recent =
> +                            metrics.data.iter().fold(0, |acc, x| acc.max(x.timestamp));
>  
> -                            for data_point in metrics.data {
> -                                most_recent_timestamp =
> -                                    most_recent_timestamp.max(data_point.timestamp);
> -                                store_metric_pbs(&remote_name_clone, &data_point);
> -                            }
> +                        sender
> +                            .send(RrdStoreRequest::Pbs {
> +                                remote: remote_name_clone,
> +                                metrics,
> +                            })
> +                            .await?;
>  
> -                            most_recent_timestamp
> -                        })
> -                        .await
> +                        Ok::<i64, Error>(most_recent)

^ ... and this are now the only values for a single `let` binding which
now looks like:

    let x = big_always_Ok_code?; // `?` op on always-Ok()
    Ok(x) // and re-OK-wrap

Could just drop the `Ok` and `?`.

>                      }
>                  }?;
>  
> @@ -106,45 +110,3 @@ async fn metric_collection_task() -> Result<(), Error> {
>          }
>      }
>  }
> -
> -fn store_metric_pve(remote_name: &str, data_point: &ClusterMetricsData) {
> -    let name = format!(
> -        "pve/{remote_name}/{id}/{metric}",
> -        id = data_point.id,
> -        metric = data_point.metric,
> -    );
> -
> -    let data_source_type = match data_point.ty {
> -        ClusterMetricsDataType::Gauge => DataSourceType::Gauge,
> -        ClusterMetricsDataType::Counter => DataSourceType::Counter,
> -        ClusterMetricsDataType::Derive => DataSourceType::Derive,
> -    };
> -
> -    rrd_cache::update_value(
> -        &name,
> -        data_point.value,
> -        data_point.timestamp,
> -        data_source_type,
> -    );
> -}
> -
> -fn store_metric_pbs(remote_name: &str, data_point: &MetricDataPoint) {
> -    let name = format!(
> -        "pbs/{remote_name}/{id}/{metric}",
> -        id = data_point.id,
> -        metric = data_point.metric,
> -    );
> -
> -    let data_source_type = match data_point.ty {
> -        MetricDataType::Gauge => DataSourceType::Gauge,
> -        MetricDataType::Counter => DataSourceType::Counter,
> -        MetricDataType::Derive => DataSourceType::Derive,
> -    };
> -
> -    rrd_cache::update_value(
> -        &name,
> -        data_point.value,
> -        data_point.timestamp,
> -        data_source_type,
> -    );
> -}
> diff --git a/server/src/metric_collection/rrd_task.rs b/server/src/metric_collection/rrd_task.rs
> new file mode 100644
> index 0000000..fe19580
> --- /dev/null
> +++ b/server/src/metric_collection/rrd_task.rs
> @@ -0,0 +1,92 @@
> +use anyhow::Error;
> +use pbs_api_types::{MetricDataPoint, MetricDataType, Metrics};
> +use proxmox_rrd::rrd::DataSourceType;
> +use pve_api_types::{ClusterMetrics, ClusterMetricsData, ClusterMetricsDataType};
> +use tokio::sync::mpsc::Receiver;
> +
> +use super::rrd_cache;
> +
> +/// Store requrest for the RRD task.
> +pub(super) enum RrdStoreRequest {
> +    /// Store PVE metrics.
> +    Pve {
> +        /// Remote name
> +        remote: String,
> +        /// Metric data
> +        metrics: ClusterMetrics,
> +    },
> +    /// Store PBS metrics.
> +    Pbs {
> +        /// Remote name
> +        remote: String,
> +        /// Metric data
> +        metrics: Metrics,
> +    },
> +}
> +
> +/// Task which stores received metrics in the RRD. Metric data is fed into
> +/// this task via a MPSC channel.
> +pub(super) async fn store_in_rrd_task(
> +    mut receiver: Receiver<RrdStoreRequest>,
> +) -> Result<(), Error> {
> +    while let Some(msg) = receiver.recv().await {
> +        //// Involves some blocking file IO
> +        tokio::task::spawn_blocking(move || match msg {
> +            RrdStoreRequest::Pve { remote, metrics } => {
> +                for data_point in metrics.data {
> +                    store_metric_pve(&remote, &data_point);
> +                }
> +            }
> +            RrdStoreRequest::Pbs { remote, metrics } => {
> +                for data_point in metrics.data {
> +                    store_metric_pbs(&remote, &data_point);
> +                }
> +            }
> +        })
> +        .await?;

^ This error won't be shown anywhere as this is the `spawn()`ed task's
entry point, and the error will stop the task for the rest of the
daemon's lifetime.

In general I prefer "detached" tasks to always return `()`.

Perhaps we should have a helper for the
`spawn_task_aborted_on_shutdown()` which enforces the `()` return type
in its generic bounds as well as a version which simply logs errors if
they are returned where we also warn in the docs that the task will then
be over for the rest of the daemon's lifetime.

> +    }
> +
> +    Ok(())
> +}
> +
> +fn store_metric_pve(remote_name: &str, data_point: &ClusterMetricsData) {
> +    let name = format!(
> +        "pve/{remote_name}/{id}/{metric}",
> +        id = data_point.id,
> +        metric = data_point.metric,
> +    );
> +
> +    let data_source_type = match data_point.ty {
> +        ClusterMetricsDataType::Gauge => DataSourceType::Gauge,
> +        ClusterMetricsDataType::Counter => DataSourceType::Counter,
> +        ClusterMetricsDataType::Derive => DataSourceType::Derive,
> +    };
> +
> +    rrd_cache::update_value(
> +        &name,
> +        data_point.value,
> +        data_point.timestamp,
> +        data_source_type,
> +    );
> +}
> +
> +fn store_metric_pbs(remote_name: &str, data_point: &MetricDataPoint) {
> +    let name = format!(
> +        "pbs/{remote_name}/{id}/{metric}",
> +        id = data_point.id,
> +        metric = data_point.metric,
> +    );
> +
> +    let data_source_type = match data_point.ty {
> +        MetricDataType::Gauge => DataSourceType::Gauge,
> +        MetricDataType::Counter => DataSourceType::Counter,
> +        MetricDataType::Derive => DataSourceType::Derive,
> +    };
> +
> +    rrd_cache::update_value(
> +        &name,
> +        data_point.value,
> +        data_point.timestamp,
> +        data_source_type,
> +    );
> +}
> -- 
> 2.39.5


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