Turn Scan memory into passive Shared Cache memory (#12295)

kunga · web-flow · commit 7d9ab3e2cb4b · 2024-12-05T09:45:49.000+01:00
diff --git a/ydb/core/tablet_flat/flat_fwd_blobs.h b/ydb/core/tablet_flat/flat_fwd_blobs.h
@@ -54,7 +54,7 @@ namespace NFwd {
             Preload(head, upper);
         }
 
-        void Fill(NPageCollection::TLoadedPage& page, EPage) noexcept override
+        void Fill(NPageCollection::TLoadedPage& page, NSharedCache::TSharedPageRef sharedPageRef, EPage) noexcept override
         {
             if (!Pages || page.PageId < Pages.front().PageId) {
                 Y_ABORT("Blobs fwd cache got page below queue");
@@ -66,7 +66,7 @@ namespace NFwd {
 
             Stat.Saved += page.Data.size();
             OnFetch -= page.Data.size();
-            OnHold += Lookup(page.PageId).Settle(page);
+            OnHold += Lookup(page.PageId).Settle(page, std::move(sharedPageRef));
 
             Shrink(false /* do not drop loading pages */);
         }
diff --git a/ydb/core/tablet_flat/flat_fwd_cache.h b/ydb/core/tablet_flat/flat_fwd_cache.h
@@ -160,7 +160,7 @@ namespace NFwd {
             }
         }
 
-        void Fill(NPageCollection::TLoadedPage& page, EPage type) noexcept override
+        void Fill(NPageCollection::TLoadedPage& page, NSharedCache::TSharedPageRef sharedPageRef, EPage type) noexcept override
         {
             Stat.Saved += page.Data.size();
             
@@ -169,7 +169,7 @@ namespace NFwd {
                 Y_ABORT_UNLESS(page.PageId == IndexPage.PageId);
                 Index.emplace(page.Data);
                 Iter = Index->LookupRow(BeginRowId);
-                IndexPage.Settle(page);
+                IndexPage.Settle(page, std::move(sharedPageRef));
                 return;
             }
 
@@ -180,7 +180,7 @@ namespace NFwd {
             
             Y_ABORT_UNLESS(page.Data.size() <= OnFetch, "Forward cache ahead counters is out of sync");
             OnFetch -= page.Data.size();
-            OnHold += it->Settle(page); // settle of a dropped page returns 0 and releases its data
+            OnHold += it->Settle(page, std::move(sharedPageRef)); // settle of a dropped page returns 0 and releases its data
 
             ShrinkPages();
         }
@@ -353,7 +353,7 @@ namespace NFwd {
             }
         }
 
-        void Fill(NPageCollection::TLoadedPage& page, EPage type) noexcept override
+        void Fill(NPageCollection::TLoadedPage& page, NSharedCache::TSharedPageRef sharedPageRef, EPage type) noexcept override
         {
             Stat.Saved += page.Data.size();
               
@@ -375,7 +375,7 @@ namespace NFwd {
                 }
             }
             
-            it->Settle(page); // settle of a dropped page releases its data
+            it->Settle(page, std::move(sharedPageRef)); // settle of a dropped page releases its data
 
             AdvancePending(levelId);
             ShrinkPages(level);
diff --git a/ydb/core/tablet_flat/flat_fwd_conf.h b/ydb/core/tablet_flat/flat_fwd_conf.h
@@ -3,12 +3,25 @@
 #include <util/system/types.h>
 #include <util/generic/array_ref.h>
 #include <util/generic/vector.h>
+#include <util/stream/format.h>
 
 namespace NKikimr {
 namespace NTable {
 namespace NFwd {
 
     struct TConf {
+        void Describe(IOutputStream &out) const noexcept
+        {
+            out
+                << "TConf{"
+                << "high=" << HumanReadableSize(AheadHi, SF_BYTES)
+                << ",low=" << HumanReadableSize(AheadLo, SF_BYTES)
+                << ",edge=" << Edge
+                << ",tablet=" << Tablet
+                << ",trace=" << Trace
+                << "}";
+        }
+
         /*_ Cache lines read ahead settings     */
 
         ui64 AheadHi = 1;
diff --git a/ydb/core/tablet_flat/flat_fwd_env.h b/ydb/core/tablet_flat/flat_fwd_env.h
@@ -150,7 +150,7 @@ namespace NFwd {
             return Get(GetQueue(part, room), ref, EPage::Opaque);
         }
 
-        void DoSave(TIntrusiveConstPtr<IPageCollection> pageCollection, ui64 cookie, TArrayRef<NPageCollection::TLoadedPage> pages)
+        void DoSave(TIntrusiveConstPtr<IPageCollection> pageCollection, ui64 cookie, TVector<NSharedCache::TEvResult::TLoaded> pages)
         {
             const ui32 epoch = ui32(cookie) - Salt;
             if (epoch < Epoch) {
@@ -167,12 +167,14 @@ namespace NFwd {
 
             for (auto& page : pages) {
                 auto type = EPage(pageCollection->Page(page.PageId).Type);
+                auto data = NSharedCache::TPinnedPageRef(page.Page).GetData();
+                NPageCollection::TLoadedPage loadedPage{page.PageId, std::move(data)};
                 if (IsIndexPage(type)) {
                     Y_ABORT_UNLESS(queue.IndexPageCollection->Label() == pageCollection->Label(), "TPart head storage doesn't match with fetch result");
-                    queue->Fill(page, type);
+                    queue->Fill(loadedPage, std::move(page.Page), type);
                 } else {
                     Y_ABORT_UNLESS(queue.GroupPageCollection->Label() == pageCollection->Label(), "TPart head storage doesn't match with fetch result");
-                    queue->Fill(page, type);
+                    queue->Fill(loadedPage, std::move(page.Page), type);
                 }
             }
         }
diff --git a/ydb/core/tablet_flat/flat_fwd_iface.h b/ydb/core/tablet_flat/flat_fwd_iface.h
@@ -3,6 +3,7 @@
 #include "flat_page_iface.h"
 #include "flat_sausage_fetch.h"
 #include "flat_fwd_misc.h"
+#include "shared_handle.h"
 
 namespace NKikimr {
 namespace NTable {
@@ -32,7 +33,7 @@ namespace NFwd {
 
         virtual TResult Get(IPageLoadingQueue *head, TPageId pageId, EPage type, ui64 lower) noexcept = 0;
         virtual void Forward(IPageLoadingQueue *head, ui64 upper) noexcept = 0;
-        virtual void Fill(NPageCollection::TLoadedPage& page, EPage type) noexcept = 0;
+        virtual void Fill(NPageCollection::TLoadedPage& page, NSharedCache::TSharedPageRef sharedPageRef, EPage type) noexcept = 0;
 
         IPageLoadingQueue* Head = nullptr; /* will be set outside of IPageLoadingLogic impl */
         TStat Stat;
diff --git a/ydb/core/tablet_flat/flat_fwd_misc.h b/ydb/core/tablet_flat/flat_fwd_misc.h
@@ -1,6 +1,7 @@
 #pragma once
 
 #include <util/stream/output.h>
+#include <util/stream/format.h>
 
 namespace NKikimr {
 namespace NTable {
@@ -18,11 +19,11 @@ namespace NFwd {
         {
             out
                 << "TFwd{"
-                << "fetch=" << Fetch
-                << ",saved=" << Saved
-                << ",usage=" << Usage
-                << ",after=" << After
-                << ",before=" << Before
+                << "fetch=" << HumanReadableSize(Fetch, SF_BYTES)
+                << ",saved=" << HumanReadableSize(Saved, SF_BYTES)
+                << ",usage=" << HumanReadableSize(Usage, SF_BYTES)
+                << ",after=" << HumanReadableSize(After, SF_BYTES)
+                << ",before=" << HumanReadableSize(Before, SF_BYTES)
                 << "}";
         }
 
diff --git a/ydb/core/tablet_flat/flat_fwd_page.h b/ydb/core/tablet_flat/flat_fwd_page.h
@@ -3,6 +3,7 @@
 #include "flat_part_iface.h"
 #include "flat_sausage_fetch.h"
 #include "flat_fwd_misc.h"
+#include "shared_handle.h"
 
 namespace NKikimr {
 namespace NTable {
@@ -31,6 +32,7 @@ namespace NFwd {
         ~TPage()
         {
             Y_ABORT_UNLESS(!Data, "Forward cache page is still holds data");
+            Y_ABORT_UNLESS(!SharedPageRef, "Forward cache page is still holds data");
         }
 
         explicit operator bool() const
@@ -53,7 +55,7 @@ namespace NFwd {
             return Data ? &Data : nullptr;
         }
 
-        ui32 Settle(NPageCollection::TLoadedPage &page) noexcept
+        ui32 Settle(NPageCollection::TLoadedPage &page, NSharedCache::TSharedPageRef ref) noexcept
         {
             const auto was = std::exchange(Fetch, EFetch::Done);
 
@@ -67,6 +69,7 @@ namespace NFwd {
                 Y_ABORT("Settling page that is not waiting for any data");
             } else {
                 Data = std::move(page.Data);
+                SharedPageRef = ref;
             }
 
             return Data.size();
@@ -90,6 +93,8 @@ namespace NFwd {
         {
             Fetch = Max(Fetch, EFetch::Drop);
 
+            SharedPageRef.Drop();
+            
             return std::exchange(Data, { });
         }
 
@@ -100,6 +105,7 @@ namespace NFwd {
         EUsage Usage    = EUsage::None;
         EFetch Fetch    = EFetch::None;
         TSharedData Data;
+        NSharedCache::TSharedPageRef SharedPageRef;
     };
 
 }
diff --git a/ydb/core/tablet_flat/flat_ops_compact.h b/ydb/core/tablet_flat/flat_ops_compact.h
@@ -364,7 +364,7 @@ namespace NTabletFlatExecutor {
 
                 logl
                     << NFmt::Do(*this) << " end=" << ui32(abort)
-                    << ", " << Blobs << "blobs " << WriteStats.Rows << "r"
+                    << ", " << Blobs << " blobs " << WriteStats.Rows << "r"
                     << " (max " << Conf->Layout.MaxRows << ")"
                     << ", put " << NFmt::If(Spent.Get());
 
diff --git a/ydb/core/tablet_flat/flat_part_loader.h b/ydb/core/tablet_flat/flat_part_loader.h
@@ -53,12 +53,20 @@ namespace NTable {
                 Y_ABORT_UNLESS(part == Part, "Unsupported part");
                 Y_ABORT_UNLESS(groupId.IsMain(), "Unsupported column group");
 
-                if (auto* savedPage = SavedPages.FindPtr(pageId)) {
-                    return savedPage;
-                } else if (auto* cached = Cache->Lookup(pageId)) {
-                    // Save page in case it's evicted on the next iteration
-                    SavedPages[pageId] = *cached;
-                    return cached;
+                auto savedPage = SavedPages.find(pageId);
+                
+                if (savedPage == SavedPages.end()) {
+                    if (auto cachedPage = Cache->GetPage(pageId); cachedPage) {
+                        if (auto sharedPageRef = cachedPage->SharedBody; sharedPageRef && sharedPageRef.Use()) {
+                            // Save page in case it's evicted on the next iteration
+                            AddSavedPage(pageId, std::move(sharedPageRef));
+                            savedPage = SavedPages.find(pageId);
+                        }
+                    }
+                }
+
+                if (savedPage != SavedPages.end()) {
+                    return &savedPage->second;
                 } else {
                     NeedPages.insert(pageId);
                     return nullptr;
@@ -86,15 +94,22 @@ namespace NTable {
                 if (cookie == 0 && NeedPages.erase(loaded.PageId)) {
                     auto pageType = Cache->GetPageType(loaded.PageId);
                     bool sticky = NeedIn(pageType) || pageType == EPage::FlatIndex;
-                    SavedPages[loaded.PageId] = NSharedCache::TPinnedPageRef(loaded.Page).GetData();
+                    AddSavedPage(loaded.PageId, loaded.Page);
                     Cache->Fill(loaded.PageId, std::move(loaded.Page), sticky);
                 }
             }
 
         private:
+            void AddSavedPage(TPageId pageId, NSharedCache::TSharedPageRef page) noexcept
+            {
+                SavedPages[pageId] = NSharedCache::TPinnedPageRef(page).GetData();
+                SavedPagesRefs.emplace_back(std::move(page));
+            }
+
             const TPart* Part = nullptr;
             TIntrusivePtr<TCache> Cache;
             THashMap<TPageId, TSharedData> SavedPages;
+            TVector<NSharedCache::TSharedPageRef> SavedPagesRefs;
             THashSet<TPageId> NeedPages;
         };
 
diff --git a/ydb/core/tablet_flat/flat_sausagecache.h b/ydb/core/tablet_flat/flat_sausagecache.h
@@ -97,11 +97,6 @@ class TPrivatePageCache {
             return PageMap.size();
         }
 
-        const TSharedData* Lookup(TPageId pageId) const noexcept {
-            auto* page = GetPage(pageId);
-            return page ? page->GetPinnedBody() : nullptr;
-        }
-
         TPage* GetPage(TPageId pageId) const noexcept {
             return PageMap[pageId].Get();
         }
diff --git a/ydb/core/tablet_flat/flat_scan_actor.h b/ydb/core/tablet_flat/flat_scan_actor.h
@@ -624,13 +624,7 @@ namespace NOps {
                 return Terminate(EAbort::Host);
             }
 
-            // TODO: would want to postpone pinning until usage
-            TVector<NPageCollection::TLoadedPage> pinned(Reserve(msg.Loaded.size()));
-            for (auto& loaded : msg.Loaded) {
-                pinned.emplace_back(loaded.PageId, TPinnedPageRef(loaded.Page).GetData());
-            }
-
-            Cache->DoSave(std::move(msg.Origin), msg.Cookie, pinned);
+            Cache->DoSave(std::move(msg.Origin), msg.Cookie, std::move(msg.Loaded));
 
             if (MayProgress()) {
                 Spent->Alter(true /* resource available again */);
diff --git a/ydb/core/tablet_flat/flat_scan_spent.h b/ydb/core/tablet_flat/flat_scan_spent.h
@@ -26,9 +26,9 @@ namespace NTable {
             const auto now = Time->Now();
 
             out
-                << "Spent{" << NFmt::TDelay(now - Fired)
-                << " wa " << NFmt::TDelay(Waits + (now - Since))
-                << " cnt " << Interrupts << "}";
+                << "Spent{time=" << NFmt::TDelay(now - Fired)
+                << ",wait=" << NFmt::TDelay(Waits + (now - Since))
+                << ",interrupts=" << Interrupts << "}";
         }
 
         void Alter(bool available) noexcept
diff --git a/ydb/core/tablet_flat/test/libs/table/test_envs.h b/ydb/core/tablet_flat/test/libs/table/test_envs.h
@@ -182,11 +182,11 @@ namespace NTest {
 
                 for (auto &seq: IndexFetch) {
                     NPageCollection::TLoadedPage page(seq, *Store->GetPage(IndexRoom, seq));
-                    PageLoadingLogic->Fill(page, Store->GetPageType(IndexRoom, seq)); /* will move data */
+                    PageLoadingLogic->Fill(page, {}, Store->GetPageType(IndexRoom, seq)); /* will move data */
                 }
                 for (auto &seq: GroupFetch) {
                     NPageCollection::TLoadedPage page(seq, *Store->GetPage(GroupRoom, seq));
-                    PageLoadingLogic->Fill(page, Store->GetPageType(GroupRoom, seq)); /* will move data */
+                    PageLoadingLogic->Fill(page, {}, Store->GetPageType(GroupRoom, seq)); /* will move data */
                 }
 
                 IndexFetch.clear();
diff --git a/ydb/core/tablet_flat/ut/ut_forward.cpp b/ydb/core/tablet_flat/ut/ut_forward.cpp
@@ -114,7 +114,7 @@ namespace {
             Shuffle(load.begin(), load.end(), Rnd);
 
             for (auto &page : load) {
-                Cache->Fill(page, EPage::Opaque);
+                Cache->Fill(page, {}, EPage::Opaque);
             }
 
             UNIT_ASSERT(Cache->Stat.Saved == Cache->Stat.Fetch);
@@ -196,7 +196,7 @@ namespace {
             Shuffle(load.begin(), load.end(), Rnd);
 
             for (auto &page : load) {
-                Cache->Fill(page, Part->GetPageType(page.PageId, {}));
+                Cache->Fill(page, {}, Part->GetPageType(page.PageId, {}));
             }
 
             UNIT_ASSERT_VALUES_EQUAL_C(Cache->Stat, stat, CurrentStepStr());
@@ -237,7 +237,7 @@ namespace {
             Shuffle(load.begin(), load.end(), Rnd);
 
             for (auto &page : load) {
-                Cache->Fill(page, Part->GetPageType(page.PageId, {}));
+                Cache->Fill(page, {}, Part->GetPageType(page.PageId, {}));
             }
 
             UNIT_ASSERT_VALUES_EQUAL_C(Cache->Stat, stat, CurrentStepStr());
diff --git a/ydb/core/tx/datashard/datashard__stats.cpp b/ydb/core/tx/datashard/datashard__stats.cpp
@@ -123,6 +123,7 @@ class TTableStatsCoroBuilder : public TActorCoroImpl, private IPages, TTableStat
         
         for (auto& loaded : msg->Loaded) {
             partPages.emplace(pageId, TPinnedPageRef(loaded.Page).GetData());
+            PageRefs.emplace_back(std::move(loaded.Page));
         }
 
         page = partPages.FindPtr(pageId);
@@ -230,6 +231,7 @@ class TTableStatsCoroBuilder : public TActorCoroImpl, private IPages, TTableStat
     }
 
     THashMap<const TPart*, THashMap<TPageId, TSharedData>> Pages;
+    TVector<TSharedPageRef> PageRefs;
     ui64 PagesSize = 0;
     ui64 CoroutineDeadline;
     TAutoPtr<TSpent> Spent;

Original file line number	Diff line number	Diff line change
`@@ -54,7 +54,7 @@ namespace NFwd {`
`54`	`54`	`Preload(head, upper);`
`55`	`55`	`}`
`56`	`56`
`57`		`- void Fill(NPageCollection::TLoadedPage& page, EPage) noexcept override`
	`57`	`+ void Fill(NPageCollection::TLoadedPage& page, NSharedCache::TSharedPageRef sharedPageRef, EPage) noexcept override`
`58`	`58`	`{`
`59`	`59`	`if (!Pages \|\| page.PageId < Pages.front().PageId) {`
`60`	`60`	`Y_ABORT("Blobs fwd cache got page below queue");`
`@@ -66,7 +66,7 @@ namespace NFwd {`
`66`	`66`
`67`	`67`	`Stat.Saved += page.Data.size();`
`68`	`68`	`OnFetch -= page.Data.size();`
`69`		`- OnHold += Lookup(page.PageId).Settle(page);`
	`69`	`+ OnHold += Lookup(page.PageId).Settle(page, std::move(sharedPageRef));`
`70`	`70`
`71`	`71`	`Shrink(false /* do not drop loading pages */);`
`72`	`72`	`}`
Original file line number	Diff line number	Diff line change
`@@ -160,7 +160,7 @@ namespace NFwd {`
`160`	`160`	`}`
`161`	`161`	`}`
`162`	`162`
`163`		`- void Fill(NPageCollection::TLoadedPage& page, EPage type) noexcept override`
	`163`	`+ void Fill(NPageCollection::TLoadedPage& page, NSharedCache::TSharedPageRef sharedPageRef, EPage type) noexcept override`
`164`	`164`	`{`
`165`	`165`	`Stat.Saved += page.Data.size();`
`166`	`166`
`@@ -169,7 +169,7 @@ namespace NFwd {`
`169`	`169`	`Y_ABORT_UNLESS(page.PageId == IndexPage.PageId);`
`170`	`170`	`Index.emplace(page.Data);`
`171`	`171`	`Iter = Index->LookupRow(BeginRowId);`
`172`		`- IndexPage.Settle(page);`
	`172`	`+ IndexPage.Settle(page, std::move(sharedPageRef));`
`173`	`173`	`return;`
`174`	`174`	`}`
`175`	`175`
`@@ -180,7 +180,7 @@ namespace NFwd {`
`180`	`180`
`181`	`181`	`Y_ABORT_UNLESS(page.Data.size() <= OnFetch, "Forward cache ahead counters is out of sync");`
`182`	`182`	`OnFetch -= page.Data.size();`
`183`		`- OnHold += it->Settle(page); // settle of a dropped page returns 0 and releases its data`
	`183`	`+ OnHold += it->Settle(page, std::move(sharedPageRef)); // settle of a dropped page returns 0 and releases its data`
`184`	`184`
`185`	`185`	`ShrinkPages();`
`186`	`186`	`}`
`@@ -353,7 +353,7 @@ namespace NFwd {`
`353`	`353`	`}`
`354`	`354`	`}`
`355`	`355`
`356`		`- void Fill(NPageCollection::TLoadedPage& page, EPage type) noexcept override`
	`356`	`+ void Fill(NPageCollection::TLoadedPage& page, NSharedCache::TSharedPageRef sharedPageRef, EPage type) noexcept override`
`357`	`357`	`{`
`358`	`358`	`Stat.Saved += page.Data.size();`
`359`	`359`
`@@ -375,7 +375,7 @@ namespace NFwd {`
`375`	`375`	`}`
`376`	`376`	`}`
`377`	`377`
`378`		`- it->Settle(page); // settle of a dropped page releases its data`
	`378`	`+ it->Settle(page, std::move(sharedPageRef)); // settle of a dropped page releases its data`
`379`	`379`
`380`	`380`	`AdvancePending(levelId);`
`381`	`381`	`ShrinkPages(level);`
Original file line number	Diff line number	Diff line change
`@@ -150,7 +150,7 @@ namespace NFwd {`
`150`	`150`	`return Get(GetQueue(part, room), ref, EPage::Opaque);`
`151`	`151`	`}`
`152`	`152`
`153`		`- void DoSave(TIntrusiveConstPtr<IPageCollection> pageCollection, ui64 cookie, TArrayRef<NPageCollection::TLoadedPage> pages)`
	`153`	`+ void DoSave(TIntrusiveConstPtr<IPageCollection> pageCollection, ui64 cookie, TVector<NSharedCache::TEvResult::TLoaded> pages)`
`154`	`154`	`{`
`155`	`155`	`const ui32 epoch = ui32(cookie) - Salt;`
`156`	`156`	`if (epoch < Epoch) {`
`@@ -167,12 +167,14 @@ namespace NFwd {`
`167`	`167`
`168`	`168`	`for (auto& page : pages) {`
`169`	`169`	`auto type = EPage(pageCollection->Page(page.PageId).Type);`
	`170`	`+ auto data = NSharedCache::TPinnedPageRef(page.Page).GetData();`
	`171`	`+ NPageCollection::TLoadedPage loadedPage{page.PageId, std::move(data)};`
`170`	`172`	`if (IsIndexPage(type)) {`
`171`	`173`	`Y_ABORT_UNLESS(queue.IndexPageCollection->Label() == pageCollection->Label(), "TPart head storage doesn't match with fetch result");`
`172`		`- queue->Fill(page, type);`
	`174`	`+ queue->Fill(loadedPage, std::move(page.Page), type);`
`173`	`175`	`} else {`
`174`	`176`	`Y_ABORT_UNLESS(queue.GroupPageCollection->Label() == pageCollection->Label(), "TPart head storage doesn't match with fetch result");`
`175`		`- queue->Fill(page, type);`
	`177`	`+ queue->Fill(loadedPage, std::move(page.Page), type);`
`176`	`178`	`}`
`177`	`179`	`}`
`178`	`180`	`}`
Original file line number	Diff line number	Diff line change
`@@ -3,6 +3,7 @@`
`3`	`3`	`#include "flat_part_iface.h"`
`4`	`4`	`#include "flat_sausage_fetch.h"`
`5`	`5`	`#include "flat_fwd_misc.h"`
	`6`	`+#include "shared_handle.h"`
`6`	`7`
`7`	`8`	`namespace NKikimr {`
`8`	`9`	`namespace NTable {`
`@@ -31,6 +32,7 @@ namespace NFwd {`
`31`	`32`	`~TPage()`
`32`	`33`	`{`
`33`	`34`	`Y_ABORT_UNLESS(!Data, "Forward cache page is still holds data");`
	`35`	`+ Y_ABORT_UNLESS(!SharedPageRef, "Forward cache page is still holds data");`
`34`	`36`	`}`
`35`	`37`
`36`	`38`	`explicit operator bool() const`
`@@ -53,7 +55,7 @@ namespace NFwd {`
`53`	`55`	`return Data ? &Data : nullptr;`
`54`	`56`	`}`
`55`	`57`
`56`		`- ui32 Settle(NPageCollection::TLoadedPage &page) noexcept`
	`58`	`+ ui32 Settle(NPageCollection::TLoadedPage &page, NSharedCache::TSharedPageRef ref) noexcept`
`57`	`59`	`{`
`58`	`60`	`const auto was = std::exchange(Fetch, EFetch::Done);`
`59`	`61`
`@@ -67,6 +69,7 @@ namespace NFwd {`
`67`	`69`	`Y_ABORT("Settling page that is not waiting for any data");`
`68`	`70`	`} else {`
`69`	`71`	`Data = std::move(page.Data);`
	`72`	`+ SharedPageRef = ref;`
`70`	`73`	`}`
`71`	`74`
`72`	`75`	`return Data.size();`
`@@ -90,6 +93,8 @@ namespace NFwd {`
`90`	`93`	`{`
`91`	`94`	`Fetch = Max(Fetch, EFetch::Drop);`
`92`	`95`
	`96`	`+ SharedPageRef.Drop();`
	`97`	`+`
`93`	`98`	`return std::exchange(Data, { });`
`94`	`99`	`}`
`95`	`100`
`@@ -100,6 +105,7 @@ namespace NFwd {`
`100`	`105`	`EUsage Usage = EUsage::None;`
`101`	`106`	`EFetch Fetch = EFetch::None;`
`102`	`107`	`TSharedData Data;`
	`108`	`+ NSharedCache::TSharedPageRef SharedPageRef;`
`103`	`109`	`};`
`104`	`110`
`105`	`111`	`}`
Original file line number	Diff line number	Diff line change
`@@ -97,11 +97,6 @@ class TPrivatePageCache {`
`97`	`97`	`return PageMap.size();`
`98`	`98`	`}`
`99`	`99`
`100`		`- const TSharedData* Lookup(TPageId pageId) const noexcept {`
`101`		`- auto* page = GetPage(pageId);`
`102`		`- return page ? page->GetPinnedBody() : nullptr;`
`103`		`- }`
`104`		`-`
`105`	`100`	`TPage* GetPage(TPageId pageId) const noexcept {`
`106`	`101`	`return PageMap[pageId].Get();`
`107`	`102`	`}`