More printing and assertions

pageserver/src/tenant/blob_io.rs

@@ -346,6 +346,7 @@ impl<const BUFFERED: bool> BlobWriter<BUFFERED> {
                     None => (BYTE_UNCOMPRESSED, len, srcbuf.slice(..).into_inner()),
                 };
                 let mut len_buf = (len_written as u32).to_be_bytes();
+                assert_eq!(len_buf[0] & 0xf0, 0);
                 len_buf[0] |= high_bit_mask;
                 io_buf.extend_from_slice(&len_buf[..]);
                 (self.write_all(io_buf, ctx).await, srcbuf)

pageserver/src/tenant/storage_layer/image_layer.rs

@@ -528,6 +528,7 @@ impl ImageLayer {
                 content_a, content_b,
                 "mismatch for key={key} cmp={cmp:?} and {path_a}:{path_b}"
             );
+            println!("match for key={key} cmp={cmp:?} from {path_a}");
         }
         Ok(())
     }