From: Inaam Rana <inaam@google.com>
Date: Fri, 17 Jul 2026 15:29:03 +0000
Subject: [PATCH] Fix dblwr performance regression in upstream

This is a fix for https://bugs.mysql.com/bug.php?id=116209. It handles two things:
1) Any zero filled pages in the dblwr are pruned out
2) For a given space_id the dblwr recovery is called only once. This protects us against calling recovery on the same space_id multiple times due to MLOG_FILE_EXTEND records in the log stream.

diff --git a/storage/innobase/buf/buf0dblwr.cc b/storage/innobase/buf/buf0dblwr.cc
index 3eb92075295..ce2a5109c90 100644
--- a/storage/innobase/buf/buf0dblwr.cc
+++ b/storage/innobase/buf/buf0dblwr.cc
@@ -45,6 +45,7 @@ Atomic writes handling. */
 #include <iomanip>
 #include <iostream>
 #include <regex>
+#include <unordered_set>
 #include <vector>
 
 /** Doublewrite buffer */
@@ -356,6 +357,9 @@ class Pages {
   /** Page entries from reduced doublewrite buffer */
   Page_entries m_page_entries;
 
+  /** Spaces that have been recovered */
+  std::unordered_set<space_id_t> m_recovered_spaces;
+
   // Disable copying
   Pages(const Pages &) = delete;
   Pages(Pages &&) = delete;
@@ -3169,6 +3173,11 @@ void recv::Pages::recover(fil_space_t *space) noexcept {
     return;
   }
 
+  if (space != nullptr && m_recovered_spaces.contains(space->id)) {
+    /* Already recovered this space. No need to do it again. */
+    return;
+  }
+
   auto recover_all = (space == nullptr);
 
   for (const auto &page : m_pages) {
@@ -3193,6 +3202,7 @@ void recv::Pages::recover(fil_space_t *space) noexcept {
       continue;
     }
 
+    m_recovered_spaces.insert(space->id);
     fil_space_open_if_needed(space);
 
     page->m_recovered =
@@ -3206,6 +3216,11 @@ void recv::Pages::recover(fil_space_t *space) noexcept {
 
 void recv::Pages::reduced_recover(fil_space_t *space) noexcept {
 #ifndef UNIV_HOTBACKUP
+  if (space != nullptr && m_recovered_spaces.contains(space->id)) {
+    /* Already recovered this space. No need to do it again. */
+    return;
+  }
+
   auto recover_all = (space == nullptr);
 
   for (const auto &entry : m_page_entries) {
@@ -3225,6 +3240,7 @@ void recv::Pages::reduced_recover(fil_space_t *space) noexcept {
       continue;
     }
 
+    m_recovered_spaces.insert(space->id);
     fil_space_open_if_needed(space);
 
     bool is_corrupted = false;
@@ -3312,6 +3328,10 @@ void recv::Pages::add(page_no_t page_no, const byte *page,
   if (!dblwr::is_enabled()) {
     return;
   }
+  if (buf_page_is_zeroes(page, univ_page_size)) {
+    return;
+  }
+
   /* Make a copy of the page contents. */
   auto dblwr_page =
       ut::new_withkey<Page>(UT_NEW_THIS_FILE_PSI_KEY, page_no, page, n_bytes);