From 436178faeedec9f4cf0494db4598db9226a96eb7 Mon Sep 17 00:00:00 2001
From: Christian Schwarz <christian@neon.tech>
Date: Thu, 20 Feb 2025 00:41:52 +0100
Subject: [PATCH] report generation in PageserverFeedback (maybe we don't need
 this if we include in Offer RPC response?)

---
 libs/utils/src/pageserver_feedback.rs | 14 +++++++++++++-
 safekeeper/src/send_wal.rs            |  2 +-
 safekeeper/src/timeline.rs            |  3 ++-
 3 files changed, 16 insertions(+), 3 deletions(-)

diff --git a/libs/utils/src/pageserver_feedback.rs b/libs/utils/src/pageserver_feedback.rs
index dede65e699..e49e2ca87a 100644
--- a/libs/utils/src/pageserver_feedback.rs
+++ b/libs/utils/src/pageserver_feedback.rs
@@ -5,7 +5,7 @@ use pq_proto::{read_cstr, PG_EPOCH};
 use serde::{Deserialize, Serialize};
 use tracing::{trace, warn};
 
-use crate::lsn::Lsn;
+use crate::{generation::Generation, lsn::Lsn};
 
 /// Feedback pageserver sends to safekeeper and safekeeper resends to compute.
 ///
@@ -32,6 +32,12 @@ pub struct PageserverFeedback {
     pub replytime: SystemTime,
     /// Used to track feedbacks from different shards. Always zero for unsharded tenants.
     pub shard_number: u32,
+    /// The shard's pageserver-side generation number.
+    /// Used to track `remote_consistent_lsn` by generation which is required
+    /// to determine whether
+    /// - WAL offers still need to be sent
+    /// - in future: whether WAL can be evicted and/or pruned
+    pub generation: Generation,
 }
 
 impl PageserverFeedback {
@@ -43,6 +49,7 @@ impl PageserverFeedback {
             disk_consistent_lsn: Lsn::INVALID,
             replytime: *PG_EPOCH,
             shard_number: 0,
+            generation: Generation::none(),
         }
     }
 
@@ -101,6 +108,8 @@ impl PageserverFeedback {
             buf.put_u32(self.shard_number);
         }
 
+        todo!("ps_generation");
+
         buf[buf_ptr] = nkeys;
     }
 
@@ -147,6 +156,9 @@ impl PageserverFeedback {
                     assert_eq!(len, 4);
                     rf.shard_number = buf.get_u32();
                 }
+                b"ps_generation" => {
+                    todo!();
+                }
                 _ => {
                     let len = buf.get_i32();
                     warn!(
diff --git a/safekeeper/src/send_wal.rs b/safekeeper/src/send_wal.rs
index 4a4a74a0fd..66584f7814 100644
--- a/safekeeper/src/send_wal.rs
+++ b/safekeeper/src/send_wal.rs
@@ -1020,7 +1020,7 @@ impl<IO: AsyncRead + AsyncWrite + Unpin> ReplyReader<IO> {
                     .walsenders
                     .record_ps_feedback(self.ws_guard.id, &ps_feedback);
                 self.tli
-                    .update_remote_consistent_lsn(ps_feedback.remote_consistent_lsn)
+                    .update_remote_consistent_lsn(ps_feedback.remote_consistent_lsn, ps_feedback.generation)
                     .await;
                 // in principle new remote_consistent_lsn could allow to
                 // deactivate the timeline, but we check that regularly through
diff --git a/safekeeper/src/timeline.rs b/safekeeper/src/timeline.rs
index 4341f13824..c1c87532db 100644
--- a/safekeeper/src/timeline.rs
+++ b/safekeeper/src/timeline.rs
@@ -11,6 +11,7 @@ use safekeeper_api::models::{
 use safekeeper_api::Term;
 use tokio::fs::{self};
 use tokio_util::sync::CancellationToken;
+use utils::generation::Generation;
 use utils::id::TenantId;
 use utils::sync::gate::Gate;
 
@@ -974,7 +975,7 @@ impl WalResidentTimeline {
     }
 
     /// Update in memory remote consistent lsn.
-    pub async fn update_remote_consistent_lsn(&self, candidate: Lsn) {
+    pub async fn update_remote_consistent_lsn(&self, candidate: Lsn, generation: Generation) {
         let mut shared_state = self.write_shared_state().await;
         shared_state.sk.state_mut().inmem.remote_consistent_lsn = max(
             shared_state.sk.state().inmem.remote_consistent_lsn,