Make the compaction warning more tolerant and reduce cut limit

neondatabase · Aug 17, 2023 · 132e3e7 · 132e3e7
1 parent 64fc7ea
commit 132e3e7
Showing 1 changed file with 10 additions and 7 deletions.
diff --git a/pageserver/src/tenant/timeline.rs b/pageserver/src/tenant/timeline.rs
@@ -3605,13 +3605,13 @@ impl Timeline {
             .iter()
             .map(|DeltaEntry { key, lsn, size, .. }| (*key, *lsn, *size))
             .coalesce(|mut prev, cur| {
-                // Coalesce keys that belong to the same key pair.
-                // This ensures that compaction doesn't put them
+                // Coalesce key pairs that have the same key.
+                // This makes compaction not put them
                 // into different layer files.
-                // Still limit this by the target file size,
-                // so that we keep the size of the files in
-                // check.
-                if prev.0 == cur.0 && prev.2 < target_file_size {
+                // Still limit this by a quarter of the target
+                // file size, so that we don't overshoot the
+                // target by too much (by at most the liimt).
+                if prev.0 == cur.0 && prev.2 < target_file_size / 4 {
                     prev.2 += cur.2;
                     Ok(prev)
                 } else {
@@ -3778,7 +3778,10 @@ impl Timeline {
         // Sync layers
         if !new_layers.is_empty() {
             // Print a warning if the created layer is larger than double the target size
-            let warn_limit = target_file_size * 2;
+            // Add two pages for potential overhead. This should in theory be already
+            // accounted for in the target calculation, but for very small targets,
+            // we still might easily hit the target.
+            let warn_limit = target_file_size * 2 + page_cache::PAGE_SZ as u64 * 2;
             for layer in new_layers.iter() {
                 if layer.desc.file_size > warn_limit {
                     warn!(