From 665369c439d6ec1d107dea7ccc80ce64b080297a Mon Sep 17 00:00:00 2001
From: Vlad Lazar <vlad@neon.tech>
Date: Wed, 11 Dec 2024 12:35:02 +0000
Subject: [PATCH] wal_decoder: fix compact key protobuf encoding (#10074)

## Problem

Protobuf doesn't support 128 bit integers, so we encode the keys as two
64 bit integers. Issue is that when we split the 128 bit compact key we
use signed 64 bit integers to represent the two halves. This may result
in a negative lower half when relnode is larger than `0x00800000`. When
we convert the lower half to an i128 we get a negative `CompactKey`.

## Summary of Changes

Use unsigned integers when encoding into Protobuf.

## Deployment

* Prod: We disabled the interpreted proto, so no compat concerns.
* Staging: Disable the interpreted proto, do one release, and then
release the fixed version.
We do this because a negative int32 will convert to a large uint32 value
and could give
a key in the actual pageserver space. In production we would around this
by adding new
fields to the proto and deprecating the old ones, but we can make our
lives easy here.
* Pre-prod: Same as staging
---
 libs/pageserver_api/src/key.rs               |  2 +-
 libs/wal_decoder/proto/interpreted_wal.proto |  4 +-
 libs/wal_decoder/src/wire_format.rs          | 65 +++++++++++++++++++-
 3 files changed, 66 insertions(+), 5 deletions(-)

diff --git a/libs/pageserver_api/src/key.rs b/libs/pageserver_api/src/key.rs
index 37dff6fe46..373329c9b4 100644
--- a/libs/pageserver_api/src/key.rs
+++ b/libs/pageserver_api/src/key.rs
@@ -24,7 +24,7 @@ pub struct Key {
 
 /// When working with large numbers of Keys in-memory, it is more efficient to handle them as i128 than as
 /// a struct of fields.
-#[derive(Clone, Copy, Hash, PartialEq, Eq, Ord, PartialOrd, Serialize, Deserialize)]
+#[derive(Clone, Copy, Hash, PartialEq, Eq, Ord, PartialOrd, Serialize, Deserialize, Debug)]
 pub struct CompactKey(i128);
 
 /// The storage key size.
diff --git a/libs/wal_decoder/proto/interpreted_wal.proto b/libs/wal_decoder/proto/interpreted_wal.proto
index 0393392c1a..d68484d30f 100644
--- a/libs/wal_decoder/proto/interpreted_wal.proto
+++ b/libs/wal_decoder/proto/interpreted_wal.proto
@@ -37,7 +37,7 @@ message ValueMeta {
 }
 
 message CompactKey {
-  int64 high = 1;
-  int64 low = 2;
+  uint64 high = 1;
+  uint64 low = 2;
 }
 
diff --git a/libs/wal_decoder/src/wire_format.rs b/libs/wal_decoder/src/wire_format.rs
index 5a343054c3..944ee5c919 100644
--- a/libs/wal_decoder/src/wire_format.rs
+++ b/libs/wal_decoder/src/wire_format.rs
@@ -236,8 +236,8 @@ impl From<ValueMeta> for proto::ValueMeta {
 impl From<CompactKey> for proto::CompactKey {
     fn from(value: CompactKey) -> Self {
         proto::CompactKey {
-            high: (value.raw() >> 64) as i64,
-            low: value.raw() as i64,
+            high: (value.raw() >> 64) as u64,
+            low: value.raw() as u64,
         }
     }
 }
@@ -354,3 +354,64 @@ impl From<proto::CompactKey> for CompactKey {
         (((value.high as i128) << 64) | (value.low as i128)).into()
     }
 }
+
+#[test]
+fn test_compact_key_with_large_relnode() {
+    use pageserver_api::key::Key;
+
+    let inputs = vec![
+        Key {
+            field1: 0,
+            field2: 0x100,
+            field3: 0x200,
+            field4: 0,
+            field5: 0x10,
+            field6: 0x5,
+        },
+        Key {
+            field1: 0,
+            field2: 0x100,
+            field3: 0x200,
+            field4: 0x007FFFFF,
+            field5: 0x10,
+            field6: 0x5,
+        },
+        Key {
+            field1: 0,
+            field2: 0x100,
+            field3: 0x200,
+            field4: 0x00800000,
+            field5: 0x10,
+            field6: 0x5,
+        },
+        Key {
+            field1: 0,
+            field2: 0x100,
+            field3: 0x200,
+            field4: 0x00800001,
+            field5: 0x10,
+            field6: 0x5,
+        },
+        Key {
+            field1: 0,
+            field2: 0xFFFFFFFF,
+            field3: 0xFFFFFFFF,
+            field4: 0xFFFFFFFF,
+            field5: 0x0,
+            field6: 0x0,
+        },
+    ];
+
+    for input in inputs {
+        assert!(input.is_valid_key_on_write_path());
+        let compact = input.to_compact();
+        let proto: proto::CompactKey = compact.into();
+        let from_proto: CompactKey = proto.into();
+
+        assert_eq!(
+            compact, from_proto,
+            "Round trip failed for key with relnode={:#x}",
+            input.field4
+        );
+    }
+}