From 394e675db31808a335f9dfeb1f2a63f1521cc545 Mon Sep 17 00:00:00 2001
From: Heikki Linnakangas <heikki@neon.tech>
Date: Sat, 27 Jan 2024 14:49:59 +0200
Subject: [PATCH] Print checkpoint key contents "pagectl print-layer-file"

---
 pageserver/src/pgdatadir_mapping.rs           |  2 +-
 .../src/tenant/storage_layer/delta_layer.rs   | 22 ++++++++++++++++---
 2 files changed, 20 insertions(+), 4 deletions(-)

diff --git a/pageserver/src/pgdatadir_mapping.rs b/pageserver/src/pgdatadir_mapping.rs
index d9cc85319e..ac9ee8d153 100644
--- a/pageserver/src/pgdatadir_mapping.rs
+++ b/pageserver/src/pgdatadir_mapping.rs
@@ -1832,7 +1832,7 @@ const CONTROLFILE_KEY: Key = Key {
     field6: 0,
 };
 
-const CHECKPOINT_KEY: Key = Key {
+pub const CHECKPOINT_KEY: Key = Key {
     field1: 0x03,
     field2: 0,
     field3: 0,
diff --git a/pageserver/src/tenant/storage_layer/delta_layer.rs b/pageserver/src/tenant/storage_layer/delta_layer.rs
index 4ded6d6a8d..645f39dfbf 100644
--- a/pageserver/src/tenant/storage_layer/delta_layer.rs
+++ b/pageserver/src/tenant/storage_layer/delta_layer.rs
@@ -884,7 +884,7 @@ impl DeltaLayerInner {
 
         let keys = self.load_keys(ctx).await?;
 
-        async fn dump_blob(val: ValueRef<'_>, ctx: &RequestContext) -> anyhow::Result<String> {
+        async fn dump_blob(val: &ValueRef<'_>, ctx: &RequestContext) -> anyhow::Result<String> {
             let buf = val.reader.read_blob(val.blob_ref.pos(), ctx).await?;
             let val = Value::des(&buf)?;
             let desc = match val {
@@ -905,14 +905,30 @@ impl DeltaLayerInner {
         }
 
         for entry in keys {
-            let DeltaEntry { key, lsn, val, .. } = entry;
-            let desc = match dump_blob(val, ctx).await {
+            let DeltaEntry { key, lsn, val, .. } = entry;            
+            let desc = match dump_blob(&val, ctx).await {
                 Ok(desc) => desc,
                 Err(err) => {
                     format!("ERROR: {err}")
                 }
             };
             println!("  key {key} at {lsn}: {desc}");
+            use crate::pgdatadir_mapping::CHECKPOINT_KEY;
+            use postgres_ffi::CheckPoint;
+            if key == CHECKPOINT_KEY
+            {
+                let buf = val.reader.read_blob(val.blob_ref.pos(), ctx).await?;
+                let val = Value::des(&buf)?;
+                match val {
+                    Value::Image(img) => {
+                        let checkpoint = CheckPoint::decode(&img)?;
+                        println!("   CHECKPOINT: {:?}", checkpoint);
+                    }
+                    Value::WalRecord(_rec) => {
+                        format!(" unexpected walrecord for checkpoint key");
+                    }
+                }
+            }
         }
 
         Ok(())