From b105c5b0dcd47d1e6f074a09ade3647d8162e869 Mon Sep 17 00:00:00 2001
From: Wojtek <wskozlowski@dbzero.io>
Date: Mon, 15 Dec 2025 10:04:03 +0100
Subject: [PATCH] refresh fixes

---
 src/dbzero/core/memory/PrefixImpl.cpp   |  7 ++++---
 src/dbzero/core/storage/BDevStorage.cpp | 27 ++++++++++++++++---------
 2 files changed, 22 insertions(+), 12 deletions(-)

diff --git a/src/dbzero/core/memory/PrefixImpl.cpp b/src/dbzero/core/memory/PrefixImpl.cpp
index f6356442..fee92bae 100644
--- a/src/dbzero/core/memory/PrefixImpl.cpp
+++ b/src/dbzero/core/memory/PrefixImpl.cpp
@@ -339,9 +339,10 @@ namespace db0
             m_cache.markAsMissing(updated_page_num, state_num);
         });
         
-        assert(result);
-        // retrieve & sync to the refreshed state number
-        m_head_state_num = m_storage_ptr->getMaxStateNum();        
+        if (result) {
+            // retrieve & sync to the refreshed state number
+            m_head_state_num = m_storage_ptr->getMaxStateNum();
+        }
         return result;
     }
     
diff --git a/src/dbzero/core/storage/BDevStorage.cpp b/src/dbzero/core/storage/BDevStorage.cpp
index 68fbd388..b7145cff 100644
--- a/src/dbzero/core/storage/BDevStorage.cpp
+++ b/src/dbzero/core/storage/BDevStorage.cpp
@@ -678,12 +678,7 @@ namespace db0
                 assert(m_ext_dram_changelog_io);
                 ext_dram_changelog_io_pos = m_ext_dram_changelog_io->getStreamPos();
             }
-            auto dp_changelog_io_pos = m_dp_changelog_io.getStreamPos();
-            std::optional<StateNumType> dram_state_num;
-            // NOTE: ext DRAM updates have incremental nature so they might preceed DRAM updates
-            // without breaking the consistency
-            std::optional<StateNumType> ext_dram_state_num;
-
+            auto dp_changelog_io_pos = m_dp_changelog_io.getStreamPos();            
             // reverts streams to previous positions
             auto revert_streams = [&]() {
                 m_dram_changelog_io.setStreamPos(dram_changelog_io_pos);
@@ -695,8 +690,15 @@ namespace db0
             };
             
             try {
-                dram_state_num = m_dram_io.beginApplyChanges(m_dram_changelog_io);
+                auto dram_state_num = m_dram_io.beginApplyChanges(m_dram_changelog_io);
+                if (!dram_state_num) {
+                    // no updates to process
+                    break;                    
+                }
                 dram_changelog_io_pos = m_dram_changelog_io.getStreamPos();
+                // NOTE: ext DRAM updates have incremental nature so they might preceed DRAM updates
+                // without breaking the consistency
+                std::optional<StateNumType> ext_dram_state_num;
                 if (!!m_ext_space) {
                     assert(m_ext_dram_changelog_io);
                     m_ext_dram_changelog_io->refresh();
@@ -704,7 +706,8 @@ namespace db0
                     ext_dram_changelog_io_pos = m_ext_dram_changelog_io->getStreamPos();
                 }
                 
-                if (dram_state_num && m_dram_io.completeApplyChanges(*dram_state_num)) {
+                assert(dram_state_num);
+                if (m_dram_io.completeApplyChanges(*dram_state_num)) {
                     // refresh underlying sparse index / diff index after DRAM update
                     m_sparse_pair.refresh();
                 }
@@ -712,8 +715,14 @@ namespace db0
                     m_ext_space.refresh();
                 }
                 
-                // this is the state number to sync-up to
+                // this is the state number to sync-up to (which must be identical as dram_state_num)
                 auto max_state_num = m_sparse_pair.getMaxStateNum();
+                if (dram_state_num != max_state_num) {
+                    // NOTE: this critical and irrecoverable error indicates corruption of the DRAM changelog stream
+                    THROWF(db0::InternalException) << "Inconsistent state: DRAM changelog state number "
+                        << *dram_state_num << " does not match max known state number " << max_state_num;
+                }
+                
                 // send all page-update notifications to the provided handler
                 if (on_page_updated) {
                     StateNumType updated_state_num = 0;