From a8d9939ea959ad8c00b376fb8e189f630d3013ab Mon Sep 17 00:00:00 2001
From: "Alex Chi Z." <4198311+skyzh@users.noreply.github.com>
Date: Thu, 7 Nov 2024 10:38:15 -0500
Subject: [PATCH] fix(pageserver): reduce aux compaction threshold (#9647)

ref https://github.com/neondatabase/neon/issues/9441

The metrics from LR publisher testing project: ~300KB aux key deltas per
256MB files. Therefore, I think we can do compaction more aggressively
as these deltas are small and compaction can reduce layer download
latency. We also have a read path perf fix
https://github.com/neondatabase/neon/pull/9631 but I'd still combine the
read path fix with the reduce of the compaction threshold.

## Summary of changes

* reduce metadata compaction threshold
* use num of L1 delta layers as an indicator for metadata compaction
* dump more logs

Signed-off-by: Alex Chi Z <chi@neon.tech>
---
 pageserver/src/pgdatadir_mapping.rs |  2 +-
 pageserver/src/tenant/timeline.rs   | 10 ++++------
 2 files changed, 5 insertions(+), 7 deletions(-)

diff --git a/pageserver/src/pgdatadir_mapping.rs b/pageserver/src/pgdatadir_mapping.rs
index 7b106569a4..7c1abbf3e2 100644
--- a/pageserver/src/pgdatadir_mapping.rs
+++ b/pageserver/src/pgdatadir_mapping.rs
@@ -45,7 +45,7 @@ use wal_decoder::serialized_batch::SerializedValueBatch;
 pub const MAX_AUX_FILE_DELTAS: usize = 1024;
 
 /// Max number of aux-file-related delta layers. The compaction will create a new image layer once this threshold is reached.
-pub const MAX_AUX_FILE_V2_DELTAS: usize = 64;
+pub const MAX_AUX_FILE_V2_DELTAS: usize = 16;
 
 #[derive(Debug)]
 pub enum LsnForTimestamp {
diff --git a/pageserver/src/tenant/timeline.rs b/pageserver/src/tenant/timeline.rs
index ee823beca8..6e082aecf5 100644
--- a/pageserver/src/tenant/timeline.rs
+++ b/pageserver/src/tenant/timeline.rs
@@ -4090,6 +4090,7 @@ impl Timeline {
     ) -> Result<ImageLayerCreationOutcome, CreateImageLayersError> {
         // Metadata keys image layer creation.
         let mut reconstruct_state = ValuesReconstructState::default();
+        let begin = Instant::now();
         let data = self
             .get_vectored_impl(partition.clone(), lsn, &mut reconstruct_state, ctx)
             .await?;
@@ -4106,14 +4107,11 @@ impl Timeline {
             (new_data, total_kb_retrieved / 1024, total_keys_retrieved)
         };
         let delta_files_accessed = reconstruct_state.get_delta_layers_visited();
+        let elapsed = begin.elapsed();
 
         let trigger_generation = delta_files_accessed as usize >= MAX_AUX_FILE_V2_DELTAS;
-        debug!(
-            trigger_generation,
-            delta_files_accessed,
-            total_kb_retrieved,
-            total_keys_retrieved,
-            "generate metadata images"
+        info!(
+            "metadata key compaction: trigger_generation={trigger_generation}, delta_files_accessed={delta_files_accessed}, total_kb_retrieved={total_kb_retrieved}, total_keys_retrieved={total_keys_retrieved}, read_time={}s", elapsed.as_secs_f64()
         );
 
         if !trigger_generation && mode == ImageLayerCreationMode::Try {