From 11c3ca676686b76741e502a11a9409c723376585 Mon Sep 17 00:00:00 2001
From: Andrew Noyes <andrew@weaselab.dev>
Date: Thu, 18 Jul 2024 14:19:11 -0700
Subject: [PATCH] Add oldest_extant_version metric

---
 ConflictSet.cpp | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/ConflictSet.cpp b/ConflictSet.cpp
index 2db0bec..13ee9dd 100644
--- a/ConflictSet.cpp
+++ b/ConflictSet.cpp
@@ -3262,6 +3262,7 @@ struct __attribute__((visibility("hidden"))) ConflictSet::Impl {
     if (n == nullptr) {
       removalKey = {};
       oldestExtantVersion = oldestVersionAtGcBegin;
+      oldest_extant_version.set(oldestExtantVersion);
       oldestVersionAtGcBegin = oldestVersionFullPrecision;
 #if DEBUG_VERBOSE && !defined(NDEBUG)
       fprintf(stderr,
@@ -3310,6 +3311,7 @@ struct __attribute__((visibility("hidden"))) ConflictSet::Impl {
         newestVersionFullPrecision = oldestVersion;
     oldest_version.set(oldestVersionFullPrecision);
     newest_version.set(newestVersionFullPrecision);
+    oldest_extant_version.set(oldestExtantVersion);
 
     tls.~WriteContext();
     new (&tls) WriteContext();
@@ -3432,6 +3434,9 @@ struct __attribute__((visibility("hidden"))) ConflictSet::Impl {
   GAUGE(oldest_version,
         "The lowest version that doesn't result in \"TooOld\" for checks");
   GAUGE(newest_version, "The version of the most recent call to addWrites");
+  GAUGE(
+      oldest_extant_version,
+      "A lower bound on the lowest version associated with an existing entry");
 #if MEASURE_CHECK_CPU_TIME
   COUNTER(check_cpu_seconds_total,
           "Total cpu seconds spent in a call to check");