wal_decoder: add an is empty method for interpreted record

libs/wal_decoder/src/models.rs

@@ -65,6 +65,18 @@ pub struct InterpretedWalRecord {
     pub xid: TransactionId,
 }
 
+impl InterpretedWalRecord {
+    /// Checks if the WAL record is empty
+    ///
+    /// An empty interpreted WAL record has no data or metadata and does not have to be sent to the
+    /// pageserver.
+    pub fn is_empty(&self) -> bool {
+        self.batch.is_empty()
+            && self.metadata_record.is_none()
+            && matches!(self.flush_uncommitted, FlushUncommittedRecords::No)
+    }
+}
+
 /// The interpreted part of the Postgres WAL record which requires metadata
 /// writes to the underlying storage engine.
 #[derive(Serialize, Deserialize)]

libs/wal_decoder/src/serialized_batch.rs

@@ -496,11 +496,16 @@ impl SerializedValueBatch {
         }
     }
 
-    /// Checks if the batch is empty
-    ///
-    /// A batch is empty when it contains no serialized values.
-    /// Note that it may still contain observed values.
+    /// Checks if the batch contains any serialized or observed values
     pub fn is_empty(&self) -> bool {
+        !self.has_data() && self.metadata.is_empty()
+    }
+
+    /// Checks if the batch contains data
+    ///
+    /// Note that if this returns false, it may still contain observed values or
+    /// a metadata record.
+    pub fn has_data(&self) -> bool {
         let empty = self.raw.is_empty();
 
         if cfg!(debug_assertions) && empty {
@@ -510,7 +515,7 @@ impl SerializedValueBatch {
                 .all(|meta| matches!(meta, ValueMeta::Observed(_))));
         }
 
-        empty
+        !empty
     }
 
     /// Returns the number of values serialized in the batch

pageserver/src/pgdatadir_mapping.rs

@@ -1055,10 +1055,9 @@ impl<'a> DatadirModification<'a> {
     }
 
     pub(crate) fn has_dirty_data(&self) -> bool {
-        !self
-            .pending_data_batch
+        self.pending_data_batch
             .as_ref()
-            .map_or(true, |b| b.is_empty())
+            .map_or(false, |b| b.has_data())
     }
 
     /// Set the current lsn
@@ -1234,7 +1233,7 @@ impl<'a> DatadirModification<'a> {
             Some(pending_batch) => {
                 pending_batch.extend(batch);
             }
-            None if !batch.is_empty() => {
+            None if batch.has_data() => {
                 self.pending_data_batch = Some(batch);
             }
             None => {

pageserver/src/tenant/timeline.rs

@@ -5788,7 +5788,7 @@ impl<'a> TimelineWriter<'a> {
         batch: SerializedValueBatch,
         ctx: &RequestContext,
     ) -> anyhow::Result<()> {
-        if batch.is_empty() {
+        if !batch.has_data() {
             return Ok(());
         }