fix: version changes after memtable rotation

Author: marvin-j97

src/tree/mod.rs

@@ -419,7 +419,7 @@ impl AbstractTree for Tree {
         // Rotate does not modify the memtable, so it cannot break snapshots
         copy.seqno = super_version.seqno;
 
-        version_history_lock.append_version(copy);
+        version_history_lock.replace_latest_version(copy);
 
         log::trace!("cleared active memtable");
     }
@@ -485,7 +485,7 @@ impl AbstractTree for Tree {
         // Rotate does not modify the memtable so it cannot break snapshots
         copy.seqno = super_version.seqno;
 
-        version_history_lock.append_version(copy);
+        version_history_lock.replace_latest_version(copy);
 
         log::trace!(
             "rotate: added memtable id={} to sealed memtables",

src/version/super_version.rs

@@ -66,11 +66,15 @@ impl SuperVersions {
         self.len().saturating_sub(1)
     }
 
-    pub(crate) fn maintenance(&mut self, folder: &Path, gc_watermark: SeqNo) -> crate::Result<()> {
+    pub fn maintenance(&mut self, folder: &Path, gc_watermark: SeqNo) -> crate::Result<()> {
         if gc_watermark == 0 {
             return Ok(());
         }
 
+        if self.free_list_len() < 1 {
+            return Ok(());
+        }
+
         log::trace!("Running manifest GC with watermark={gc_watermark}");
 
         if let Some(hi_idx) = self.0.iter().rposition(|x| x.seqno < gc_watermark) {
@@ -140,6 +144,12 @@ impl SuperVersions {
         self.0.push_back(version);
     }
 
+    pub fn replace_latest_version(&mut self, version: SuperVersion) {
+        if self.0.pop_back().is_some() {
+            self.0.push_back(version);
+        }
+    }
+
     pub fn latest_version(&self) -> SuperVersion {
         self.0
             .iter()