pageserver: tweak oversized key read path warning (#9221)

## Problem

`Oversized vectored read [...]` logs are spewing in prod because we have
a few keys that
are unexpectedly large:
* reldir/relblock - these are unbounded, so it's known technical debt
* slru block - they can be a bit bigger than 128KiB due to storage
format overhead

## Summary of changes

* Bump threshold to 130KiB
* Don't warn on oversized reldir and dbdir keys 

Closes https://github.com/neondatabase/neon/issues/8967

pageserver/src/tenant/storage_layer/delta_layer.rs

@@ -53,6 +53,7 @@ use camino::{Utf8Path, Utf8PathBuf};
 use futures::StreamExt;
 use itertools::Itertools;
 use pageserver_api::config::MaxVectoredReadBytes;
+use pageserver_api::key::DBDIR_KEY;
 use pageserver_api::keyspace::KeySpace;
 use pageserver_api::models::ImageCompressionAlgorithm;
 use pageserver_api::shard::TenantShardId;
@@ -963,14 +964,25 @@ impl DeltaLayerInner {
                 .blobs_at
                 .as_slice()
                 .iter()
-                .map(|(_, blob_meta)| format!("{}@{}", blob_meta.key, blob_meta.lsn))
+                .filter_map(|(_, blob_meta)| {
+                    if blob_meta.key.is_rel_dir_key() || blob_meta.key == DBDIR_KEY {
+                        // The size of values for these keys is unbounded and can
+                        // grow very large in pathological cases.
+                        None
+                    } else {
+                        Some(format!("{}@{}", blob_meta.key, blob_meta.lsn))
+                    }
+                })
                 .join(", ");
-            tracing::warn!(
-                "Oversized vectored read ({} > {}) for keys {}",
-                largest_read_size,
-                read_size_soft_max,
-                offenders
-            );
+
+            if !offenders.is_empty() {
+                tracing::warn!(
+                    "Oversized vectored read ({} > {}) for keys {}",
+                    largest_read_size,
+                    read_size_soft_max,
+                    offenders
+                );
+            }
         }
 
         largest_read_size