pagebench: add idle-streams (#12583)

## Problem

For the communicator scheduling policy, we need to understand the
server-side cost of idle gRPC streams.

Touches #11735.

## Summary of changes

Add an `idle-streams` benchmark to `pagebench` which opens a large
number of idle gRPC GetPage streams.

pageserver/pagebench/src/cmd/idle_streams.rs

@@ -0,0 +1,127 @@
+use std::sync::Arc;
+
+use anyhow::anyhow;
+use futures::StreamExt;
+use tonic::transport::Endpoint;
+use tracing::info;
+
+use pageserver_page_api::{GetPageClass, GetPageRequest, GetPageStatusCode, ReadLsn, RelTag};
+use utils::id::TenantTimelineId;
+use utils::lsn::Lsn;
+use utils::shard::ShardIndex;
+
+/// Starts a large number of idle gRPC GetPage streams.
+#[derive(clap::Parser)]
+pub(crate) struct Args {
+    /// The Pageserver to connect to. Must use grpc://.
+    #[clap(long, default_value = "grpc://localhost:51051")]
+    server: String,
+    /// The Pageserver HTTP API.
+    #[clap(long, default_value = "http://localhost:9898")]
+    http_server: String,
+    /// The number of streams to open.
+    #[clap(long, default_value = "100000")]
+    count: usize,
+    /// Number of streams per connection.
+    #[clap(long, default_value = "100")]
+    per_connection: usize,
+    /// Send a single GetPage request on each stream.
+    #[clap(long, default_value_t = false)]
+    send_request: bool,
+}
+
+pub(crate) fn main(args: Args) -> anyhow::Result<()> {
+    let rt = tokio::runtime::Builder::new_multi_thread()
+        .enable_all()
+        .build()?;
+
+    rt.block_on(main_impl(args))
+}
+
+async fn main_impl(args: Args) -> anyhow::Result<()> {
+    // Discover a tenant and timeline to use.
+    let mgmt_api_client = Arc::new(pageserver_client::mgmt_api::Client::new(
+        reqwest::Client::new(),
+        args.http_server.clone(),
+        None,
+    ));
+    let timelines: Vec<TenantTimelineId> = crate::util::cli::targets::discover(
+        &mgmt_api_client,
+        crate::util::cli::targets::Spec {
+            limit_to_first_n_targets: Some(1),
+            targets: None,
+        },
+    )
+    .await?;
+    let ttid = timelines
+        .first()
+        .ok_or_else(|| anyhow!("no timelines found"))?;
+
+    // Set up the initial client.
+    let endpoint = Endpoint::from_shared(args.server.clone())?;
+
+    let connect = async || {
+        pageserver_page_api::Client::new(
+            endpoint.connect().await?,
+            ttid.tenant_id,
+            ttid.timeline_id,
+            ShardIndex::unsharded(),
+            None,
+            None,
+        )
+    };
+
+    let mut client = connect().await?;
+    let mut streams = Vec::with_capacity(args.count);
+
+    // Create streams.
+    for i in 0..args.count {
+        if i % 100 == 0 {
+            info!("opened {}/{} streams", i, args.count);
+        }
+        if i % args.per_connection == 0 && i > 0 {
+            client = connect().await?;
+        }
+
+        let (req_tx, req_rx) = tokio::sync::mpsc::unbounded_channel();
+        let req_stream = tokio_stream::wrappers::UnboundedReceiverStream::new(req_rx);
+        let mut resp_stream = client.get_pages(req_stream).await?;
+
+        // Send request if specified.
+        if args.send_request {
+            req_tx.send(GetPageRequest {
+                request_id: 1.into(),
+                request_class: GetPageClass::Normal,
+                read_lsn: ReadLsn {
+                    request_lsn: Lsn::MAX,
+                    not_modified_since_lsn: Some(Lsn(1)),
+                },
+                rel: RelTag {
+                    spcnode: 1664, // pg_global
+                    dbnode: 0,     // shared database
+                    relnode: 1262, // pg_authid
+                    forknum: 0,    // init
+                },
+                block_numbers: vec![0],
+            })?;
+            let resp = resp_stream
+                .next()
+                .await
+                .transpose()?
+                .ok_or_else(|| anyhow!("no response"))?;
+            if resp.status_code != GetPageStatusCode::Ok {
+                return Err(anyhow!("{} response", resp.status_code));
+            }
+        }
+
+        // Hold onto streams to avoid closing them.
+        streams.push((req_tx, resp_stream));
+    }
+
+    info!("opened {} streams, sleeping", args.count);
+
+    // Block forever, to hold the idle streams open for inspection.
+    futures::future::pending::<()>().await;
+
+    Ok(())
+}

pageserver/pagebench/src/main.rs

@@ -17,6 +17,7 @@ mod cmd {
     pub(super) mod aux_files;
     pub(super) mod basebackup;
     pub(super) mod getpage_latest_lsn;
+    pub(super) mod idle_streams;
     pub(super) mod ondemand_download_churn;
     pub(super) mod trigger_initial_size_calculation;
 }
@@ -29,6 +30,7 @@ enum Args {
     TriggerInitialSizeCalculation(cmd::trigger_initial_size_calculation::Args),
     OndemandDownloadChurn(cmd::ondemand_download_churn::Args),
     AuxFiles(cmd::aux_files::Args),
+    IdleStreams(cmd::idle_streams::Args),
 }
 
 fn main() {
@@ -49,6 +51,7 @@ fn main() {
         }
         Args::OndemandDownloadChurn(args) => cmd::ondemand_download_churn::main(args),
         Args::AuxFiles(args) => cmd::aux_files::main(args),
+        Args::IdleStreams(args) => cmd::idle_streams::main(args),
     }
     .unwrap()
 }