From 1c775bdcacaa7779d61d422fe56af27b40e4606d Mon Sep 17 00:00:00 2001
From: Eric Seppanen <eds@reric.net>
Date: Sun, 25 Apr 2021 10:43:06 -0700
Subject: [PATCH] Drop LSNs from PageCacheStats

There's no clear way to sum LSNs across timelines, so just remove them
for now.
---
 pageserver/src/page_cache.rs | 27 +++++----------------------
 pageserver/src/tui.rs        | 10 +++++++++-
 2 files changed, 14 insertions(+), 23 deletions(-)

diff --git a/pageserver/src/page_cache.rs b/pageserver/src/page_cache.rs
index 55e4491c4c..667b16fb90 100644
--- a/pageserver/src/page_cache.rs
+++ b/pageserver/src/page_cache.rs
@@ -39,7 +39,7 @@ use bytes::{Buf, BufMut, Bytes, BytesMut};
 use lazy_static::lazy_static;
 use log::*;
 use rocksdb;
-use std::cmp::{max, min};
+use std::cmp::min;
 use std::collections::HashMap;
 use std::sync::atomic::AtomicU64;
 use std::sync::atomic::Ordering;
@@ -84,25 +84,14 @@ pub struct PageCacheStats {
     pub num_page_images: u64,
     pub num_wal_records: u64,
     pub num_getpage_requests: u64,
-    pub first_valid_lsn: Lsn,
-    pub last_valid_lsn: Lsn,
-    pub last_record_lsn: Lsn,
 }
 
 impl AddAssign for PageCacheStats {
     fn add_assign(&mut self, other: Self) {
-        *self = Self {
-            num_entries: self.num_entries + other.num_entries,
-            num_page_images: self.num_page_images + other.num_page_images,
-            num_wal_records: self.num_wal_records + other.num_wal_records,
-            num_getpage_requests: self.num_getpage_requests + other.num_getpage_requests,
-
-            // FIXME: needs review
-            // What should be happening here? I'm not sure what is the desired result.
-            first_valid_lsn: min(self.first_valid_lsn, other.first_valid_lsn),
-            last_valid_lsn: max(self.last_valid_lsn, other.last_valid_lsn),
-            last_record_lsn: max(self.last_record_lsn, other.last_record_lsn),
-        }
+        self.num_entries += other.num_entries;
+        self.num_page_images += other.num_page_images;
+        self.num_wal_records += other.num_wal_records;
+        self.num_getpage_requests += other.num_getpage_requests;
     }
 }
 
@@ -769,9 +758,6 @@ impl PageCache {
             num_page_images: self.num_page_images.load(Ordering::Relaxed),
             num_wal_records: self.num_wal_records.load(Ordering::Relaxed),
             num_getpage_requests: self.num_getpage_requests.load(Ordering::Relaxed),
-            first_valid_lsn: self.first_valid_lsn.load(),
-            last_valid_lsn: self.last_valid_lsn.load(),
-            last_record_lsn: self.last_record_lsn.load(),
         }
     }
 
@@ -984,9 +970,6 @@ pub fn get_stats() -> PageCacheStats {
         num_page_images: 0,
         num_wal_records: 0,
         num_getpage_requests: 0,
-        first_valid_lsn: Lsn(0),
-        last_valid_lsn: Lsn(0),
-        last_record_lsn: Lsn(0),
     };
 
     pcaches.iter().for_each(|(_sys_id, pcache)| {
diff --git a/pageserver/src/tui.rs b/pageserver/src/tui.rs
index 188ee54e11..c0e1d657b3 100644
--- a/pageserver/src/tui.rs
+++ b/pageserver/src/tui.rs
@@ -240,7 +240,9 @@ fn get_metric_u64(title: &str, value: u64) -> Spans {
     ])
 }
 
-fn get_metric_str<'a>(title: &str, value: &'a str) -> Spans<'a> {
+// This is not used since LSNs were removed from page cache stats.
+// Maybe it will be used in the future?
+fn _get_metric_str<'a>(title: &str, value: &'a str) -> Spans<'a> {
     Spans::from(vec![
         Span::styled(format!("{:<20}", title), Style::default()),
         Span::raw(": "),
@@ -261,6 +263,10 @@ impl tui::widgets::Widget for MetricsWidget {
         let mut lines: Vec<Spans> = Vec::new();
 
         let page_cache_stats = crate::page_cache::get_stats();
+
+        // This is not used since LSNs were removed from page cache stats.
+        // Maybe it will be used in the future?
+        /*
         let lsnrange = format!(
             "{} - {}",
             page_cache_stats.first_valid_lsn, page_cache_stats.last_valid_lsn
@@ -268,6 +274,8 @@ impl tui::widgets::Widget for MetricsWidget {
         let last_valid_recordlsn_str = page_cache_stats.last_record_lsn.to_string();
         lines.push(get_metric_str("Valid LSN range", &lsnrange));
         lines.push(get_metric_str("Last record LSN", &last_valid_recordlsn_str));
+        */
+
         lines.push(get_metric_u64(
             "# of cache entries",
             page_cache_stats.num_entries,