From 3302d8a1a4bce32e3a22dc23d7470d68f961cbf6 Mon Sep 17 00:00:00 2001
From: Christian Schwarz <me@cschwarz.com>
Date: Fri, 3 Nov 2023 11:57:52 +0000
Subject: [PATCH] no-op pagestream request/response type (server-side impl)

---
 libs/pageserver_api/src/models.rs | 14 ++++++++++++++
 pageserver/src/metrics.rs         |  1 +
 pageserver/src/page_service.rs    |  5 +++++
 trace/src/main.rs                 |  1 +
 4 files changed, 21 insertions(+)

diff --git a/libs/pageserver_api/src/models.rs b/libs/pageserver_api/src/models.rs
index fd433b1fa4..b4a36f5afe 100644
--- a/libs/pageserver_api/src/models.rs
+++ b/libs/pageserver_api/src/models.rs
@@ -612,15 +612,18 @@ pub enum PagestreamFeMessage {
     Nblocks(PagestreamNblocksRequest),
     GetPage(PagestreamGetPageRequest),
     DbSize(PagestreamDbSizeRequest),
+    NoOp,
 }
 
 // Wrapped in libpq CopyData
+#[derive(Debug)]
 pub enum PagestreamBeMessage {
     Exists(PagestreamExistsResponse),
     Nblocks(PagestreamNblocksResponse),
     GetPage(PagestreamGetPageResponse),
     Error(PagestreamErrorResponse),
     DbSize(PagestreamDbSizeResponse),
+    NoOp,
 }
 
 #[derive(Debug, PartialEq, Eq)]
@@ -719,6 +722,10 @@ impl PagestreamFeMessage {
                 bytes.put_u64(req.lsn.0);
                 bytes.put_u32(req.dbnode);
             }
+
+            Self::NoOp => {
+                bytes.put_u8(4);
+            }
         }
 
         bytes.into()
@@ -769,6 +776,7 @@ impl PagestreamFeMessage {
                 lsn: Lsn::from(body.read_u64::<BigEndian>()?),
                 dbnode: body.read_u32::<BigEndian>()?,
             })),
+            4 => Ok(PagestreamFeMessage::NoOp),
             _ => bail!("unknown smgr message tag: {:?}", msg_tag),
         }
     }
@@ -803,6 +811,9 @@ impl PagestreamBeMessage {
                 bytes.put_u8(104); /* tag from pagestore_client.h */
                 bytes.put_i64(resp.db_size);
             }
+            Self::NoOp => {
+                bytes.put_u8(105);
+            }
         }
 
         bytes.into()
@@ -834,6 +845,9 @@ impl PagestreamBeMessage {
                 }))
             }
             104 => todo!(),
+            105 => {
+                Ok(PagestreamBeMessage::NoOp)
+            },
             _ => bail!("unknown tag: {:?}", msg_tag),
         }
     }
diff --git a/pageserver/src/metrics.rs b/pageserver/src/metrics.rs
index 34575d93b2..5354672c1a 100644
--- a/pageserver/src/metrics.rs
+++ b/pageserver/src/metrics.rs
@@ -760,6 +760,7 @@ pub enum SmgrQueryType {
     GetRelSize,
     GetPageAtLsn,
     GetDbSize,
+    NoOp,
 }
 
 #[derive(Debug)]
diff --git a/pageserver/src/page_service.rs b/pageserver/src/page_service.rs
index 536334d051..e1fa41686d 100644
--- a/pageserver/src/page_service.rs
+++ b/pageserver/src/page_service.rs
@@ -488,6 +488,11 @@ impl PageServerHandler {
                         span,
                     )
                 }
+                PagestreamFeMessage::NoOp => {
+                    let _timer = metrics.start_timer(metrics::SmgrQueryType::NoOp);
+                    let span = tracing::info_span!("no_op");
+                    (Ok(PagestreamBeMessage::NoOp), span)
+                }
             };
 
             let response = response.unwrap_or_else(|e| {
diff --git a/trace/src/main.rs b/trace/src/main.rs
index ddd970e95d..9b20ed99c4 100644
--- a/trace/src/main.rs
+++ b/trace/src/main.rs
@@ -74,6 +74,7 @@ fn analyze_trace<R: std::io::Read>(mut reader: R) {
                 prev = Some(req);
             }
             PagestreamFeMessage::DbSize(_) => {}
+            PagestreamFeMessage::NoOp => {},
         };
     }