一：背景
1. 講故事
七月中旬有一位朋友加wx求助，他的程式在生產上跑著跑著記憶體就飆起來了，貌似沒有回頭的趨勢，詢問如何解決，截圖如下：
和這位朋友聊下來，感覺像是自己在小縣城當了個小老闆，規律的生活，有當地資源，各種小關係，有一股財務自由的味道，這也是我一直嚮往的生活方式 ???。
既然朋友找到我了，我得想辦法給他解決問題，既然是記憶體暴漲，我就賭一把在託管層面吧，嘿嘿，上windbg說話。
二： windbg 分析
1. 託管還是非託管
一直在追這個系列的朋友應該知道，我無數次的用 !address -summary 和 !eeheap -gc 這兩個命令來判斷當前記憶體屬於託管層還是非託管層。
0:000> !address -summary
--- State Summary ---------------- RgnCount ----------- Total Size -------- %ofBusy %ofTotal
MEM_FREE 393 7dfe`f2105000 ( 125.996 TB) 98.43%
MEM_RESERVE 1691 200`0f1e4000 ( 2.000 TB) 99.81% 1.56%
MEM_COMMIT 6191 0`fed07000 ( 3.981 GB) 0.19% 0.00%
0:000> !eeheap -gc
Number of GC Heaps: 1
generation 0 starts at 0x000001D2E572BBC8
generation 1 starts at 0x000001D2E54F70E0
generation 2 starts at 0x000001D252051000
ephemeral segment allocation context: none
segment begin allocated size
000001D252050000 000001D252051000 000001D26204FFE0 0xfffefe0(268431328)
Large object heap starts at 0x000001D262051000
segment begin allocated size
000001D262050000 000001D262051000 000001D2655F3F80 0x35a2f80(56242048)
Total Size: Size: 0xbf4dbf80 (3209543552) bytes.
------------------------------
GC Heap Size: Size: 0xbf4dbf80 (3209543552) bytes.
卦象上程式指標為 3.98G ，GC堆指標為 3209543552 = 3G ，很顯然，本次事故屬於 託管層面。
2. 尋找託管層上的大物件
我們都知道C#是託管語言，所以甭管有用沒用的物件都逃不出GC堆，言外之意就是看GC堆準沒錯，挑幾個大物件看看。
0:000> !dumpheap -stat
Statistics:
MT Count TotalSize Class Name
00007ff98a68f090 391475 43869284 System.Int32[]
00007ff98b6adfa0 1902760 45666240 System.Collections.ObjectModel.ReadOnlyCollection`1[[System.Linq.Expressions.Expression, System.Linq.Expressions]]
00007ff98b6ac3c0 1951470 46835280 System.Linq.Expressions.ConstantExpression
00007ff98bc452e0 1681178 53797696 System.Linq.Expressions.TypedConstantExpression
00007ff98eacb6b8 1902708 60886656 System.Dynamic.Utils.ListArgumentProvider
00007ff98f236518 1774982 70999280 Microsoft.EntityFrameworkCore.Query.Expressions.ColumnExpression
00007ff98c650c58 1681142 80694816 System.Linq.Expressions.MethodCallExpression3
00007ff98a82bc38 3414094 81938256 System.RuntimeMethodHandle
00007ff98fd96fc0 17750 83936016 System.Collections.Generic.Dictionary`2+Entry[[System.Reflection.MemberInfo, System.Private.CoreLib],[System.Linq.Expressions.Expression, System.Linq.Expressions]][]
00007ff98e5ed5d8 35493 101740504 System.Collections.Generic.Dictionary`2+Entry[[Microsoft.Extensions.DependencyInjection.ServiceLookup.ServiceCacheKey, Microsoft.Extensions.DependencyInjection],[System.Object, System.Private.CoreLib]][]
00007ff98bcff6a8 3639389 116460448 System.Linq.Expressions.PropertyExpression
00007ff98b85cf00 5028347 160907104 System.Reflection.Emit.GenericFieldInfo
00007ff98a671e18 2178117 168395994 System.String
00007ff98a5b6610 160565 171498416 System.Object[]
00007ff98eaa8ab0 4981589 199263560 System.Linq.Expressions.MemberAssignment
00007ff98a672360 398740 391928469 System.Byte[]
00007ff98a746d68 181886 486150592 System.Char[]
從託管堆上看，System.Linq.Expressions.MemberAssignment 物件高達 498w ，很明顯有問題，從類名看可能和 ExpressionTree 有關，那就抽幾個物件看看它的引用鏈上是否有過大的物件。
0:000> !gcroot 000001d25399f690
HandleTable:
000001D251B715A8 (pinned handle)
-> 000001D262068CF0 System.Object[]
-> 000001D2531C3B78 Microsoft.EntityFrameworkCore.Internal.ServiceProviderCache
-> 000001D25399E3D0 Remotion.Linq.QueryModel
-> 000001D25399E3B8 Remotion.Linq.Clauses.SelectClause
-> 000001D25442C068 System.Linq.Expressions.MemberInitExpression
-> 000001D25442C050 System.Runtime.CompilerServices.TrueReadOnlyCollection`1[[System.Linq.Expressions.MemberBinding, System.Linq.Expressions]]
-> 000001D2539A0290 System.Linq.Expressions.MemberBinding[]
-> 000001D25399F690 System.Linq.Expressions.MemberAssignment
引用鏈特別長，這裡我就擷取一下，經過一頓排查，我發現大物件居然是 Remotion.Linq.Clauses.SelectClause，objsize 這個物件直接爆掉了，真的很奇葩，如下程式碼所示：
0:000> !objsize 000001D25399E3B8
sizeof(000001D25399E3B8) = -1187378032 (0xb93a0c90) bytes (Remotion.Linq.Clauses.SelectClause)
有點懵，這個物件居然是罪魁禍首，從引用鏈看它是 EF 下的一個構建表示式樹的小部件，可以肯定的是，朋友在用EF的時候出了什麼問題，不過還得硬著頭皮繼續挖 SelectClause，經過深挖，我發現這個類有大量這樣的 char[] 陣列，匯出來後大概是下面這樣。
Logistics.Text30),
| Text31 = string TryReadValue(t1.Outer.Outer, 42, WmsOutboundConfirmLogistics.Text31),
| Text32 = string TryReadValue(t1.Outer.Outer, 43, WmsOutboundConfirmLogistics.Text32),
| Text33 = string TryReadValue(t1.Outer.Outer, 44, WmsOutboundConfirmLogistics.Text33),
| Text34 = string TryReadValue(t1.Outer.Outer, 45, WmsOutboundConfirmLogistics.Text34),
| Text35 = string TryReadValue(t1.Outer.Outer, 46, WmsOutboundConfirmLogistics.Text35),
| IsQueue = Nullable<bool> TryReadValue(t1.Outer.Outer, 47, WmsOutboundConfirmLogistics.IsQueue),
| IsStop = Nullable<bool> TryReadValue(t1.Outer.Outer, 48, WmsOutboundConfirmLogistics.IsStop),
| CheckCode = string TryReadValue(t1.Outer.Outer, 49, WmsOutboundConfirmLogistics.CheckCode),
| ClientCode = string TryReadValue(t1.Outer.Inner, 50, WmsOutboundOrder.ClientCode),
| WarehouseCode = string TryReadValue(t1.Outer.Inner, 51, WmsOutboundOrder.WarehouseCode),
| ErpNumber = string TryReadValue(t1.Outer.Inner, 52, WmsOutboundOrder.ErpNumber),
| OrderCategory = string TryReadValue(t1.Outer.Inner, 53, WmsOutboundOrder.OrderCategory),
| OrderStatus = string TryReadValue(t1.Outer.Inner, 54, WmsOutboundOrder.OrderStatus),
| OrderType = string TryReadValue(t1.Outer.Inner, 55, WmsOutboundOrder.OrderType),
| SendCompany = string TryReadValue(t1.Outer.Inner, 56, WmsOutboundOrder.SendCompany),
| SendName = string TryReadValue(t1.Outer.Inner, 57, WmsOutboundOrder.SendName),
| SendTel = string TryReadValue(t1.Outer.Inner, 58, WmsOutboundOrder.SendTel),
| SendMobile = string TryReadValue(t1.Outer.Inner, 59, WmsOutboundOrder.SendMobile),
| SendProvince = string TryReadValue(t1.Outer.Inner, 60, WmsOutboundOrder.SendProvince),
| SendCity = string TryReadValue(t1.Outer.Inner, 61, WmsOutboundOrder.SendCity),
| SendArea = string TryReadValue(t1.Outer.Inner, 62, WmsOutboundOrder.SendArea),
| ...
| CategoryName = string TryReadValue(t1.Outer.Inner, 88, WmsOutboundOrder.CategoryName),
| SourcePlatformCode = string TryReadValue(t1.Outer.Inner, 89, WmsOutboundOrder.SourcePlatformCode),
| PayMode = (string)string TryReadValue(t1.Outer.Outer, 90, null),
| List = List<WmsOutboundConfirmLogisticsLinesDTO> WmsOutboundConfirmLogisticsBusiness.GetOrderLines(string TryReadValue(t1.Outer.Outer, 5, WmsOutboundConfirmLogistics.OrderNumber)),
| ConfirmTime = DateTime TryReadValue(t1.Inner, 91, WmsOutboundOrderConfirmation.CreateTime),
| ReturnUrl = (string)string TryReadValue(t1.Outer.Outer, 92, null)
| }
|__ ),
|__ contextType: Core.DataRepository.BaseDbContext,
|__ logger: DiagnosticsLogger<Query>,
|__ queryContext: Unhandled parameter: queryContext)
從內容看，應該是 select 語句的ExpressionTree表示，問了下朋友，說大概是報表業務，不過這些資訊給他貌似也沒有多大幫助，說實話到這裡我其實也不知道怎麼繼續往下排查了，陷入了絕望。
3. 從絕望中尋找希望
我在想，既然EF構建了大量這樣的 ExpressionTree，肯定有問題，但也想不出是什麼問題，隔了半天，我突然靈光一現，EF既然構建了樹，有可能sql也出來了，對，我何不直接在 heap 上搜尋 select 的sql語句。。。。
0:000> !strings /m:*select*
Address Gen Length Value
000001d2e4de64e0 2 1964 SELECT a."Id", a."CreateTime" AS "CreateTime0", a."CreatorId", a."CreatorRealName", a."Deleted", a."OrderNumber", a."CarrierId",...
000001d2e4e11e78 2 1964 SELECT a."Id", a."CreateTime" AS "CreateTime0", a."CreatorId", a."CreatorRealName", a."Deleted", a."OrderNumber", a."CarrierId",...
000001d2e4e3d1f0 2 1964 SELECT a."Id", a."CreateTime" AS "CreateTime0", a."CreatorId", a."CreatorRealName", a."Deleted", a."OrderNumber", a."CarrierId",...
000001d2e4e673c8 2 1964 SELECT a."Id", a."CreateTime" AS "CreateTime0", a."CreatorId", a."CreatorRealName", a."Deleted", a."OrderNumber", a."CarrierId",...
000001d2e4e91760 2 1964 SELECT a."Id", a."CreateTime" AS "CreateTime0", a."CreatorId", a."CreatorRealName", a."Deleted", a."OrderNumber", a."CarrierId",...
000001d2e4ebb2e8 2 1964 SELECT a."Id", a."CreateTime" AS "CreateTime0", a."CreatorId", a."CreatorRealName", a."Deleted", a."OrderNumber", a."CarrierId",...
000001d2e4ee54f8 2 1964 SELECT a."Id", a."CreateTime" AS "CreateTime0", a."CreatorId", a."CreatorRealName", a."Deleted", a."OrderNumber", a."CarrierId",...
000001d2e4f10758 2 1964 SELECT a."Id", a."CreateTime" AS "CreateTime0", a."CreatorId", a."CreatorRealName", a."Deleted", a."OrderNumber", a."CarrierId",...
000001d2e4f398d0 2 1964 SELECT a."Id", a."CreateTime" AS "CreateTime0", a."CreatorId", a."CreatorRealName", a."Deleted", a."OrderNumber", a."CarrierId",...
---------------------------------------
18128 matching strings
果然發現了大量重複的 select 語句，而且從最左邊的記憶體地址看都是非常接近的，也就說明他們是在某一個操作中同時生成的，然後我們匯出幾個sql語句。
SELECT a."Id", ....
FROM "WmsOutboundConfirmLogistics" AS a
INNER JOIN "WmsOutboundOrder" AS b ON a."OrderNumber" = b."OrderNumber"
INNER JOIN "WmsOutboundOrderConfirmation" AS c ON a."OrderNumber" = c."OrderNumber"
WHERE (a."OrderNumber" = @__pagination_OrderNumber_0) AND (b."FreezeStatus" = FALSE)
ORDER BY a."Id"";
SELECT a."Id", ....
FROM "WmsOutboundConfirmLogistics" AS a
INNER JOIN "WmsOutboundOrder" AS b ON a."OrderNumber" = b."OrderNumber"
INNER JOIN "WmsOutboundOrderConfirmation" AS c ON a."OrderNumber" = c."OrderNumber"
WHERE (a."OrderNumber" = @__pagination_OrderNumber_0) AND (b."FreezeStatus" = FALSE)
ORDER BY a."Id""
拿到這 1.8w 重複的sql 給朋友看，朋友說這是查詢報表的sql。
4. 所有線索整合打通
那這裡就存在著很大問題，既然是查詢報表，為什麼會有 1.8w 相同的sql，唯一不同的就是 a."OrderNumber" = @__pagination_OrderNumber_0 中的訂單號，難道不應該是 a.OrderNumber in (xxxx) 或者是表關聯查詢嗎？？？ 整理一下就是下面這樣的猜想：
-- 理想
select * from a where a.id in (1,2,3)
-- 現實
select * from a where a.id=1;
select * from a where a.id=2;
select * from a where a.id=3;
加上每個sql記憶體地址相近，再結合爆表的 Remotion.Linq.Clauses.SelectClause 物件，整個流程大概就是：本該表關聯或者in操作，結果變成了無數個單條sql語句查詢，導致EF底層出現記憶體爆炸式增長。
三：總結
看了下朋友查詢ef的寫法，猜測大多都是人肉構建 ExpressionTree 去查詢資料庫，大寫的??，比如下面的這張圖：
解決方案就是讓朋友檢查下表示式樹的寫法問題，或者直接灌寫好的sql得了，說實話這個dump還是費了九牛二虎之力，本以為很簡單，實操起來還是碰到了一點小困難，就當歷練成長吧！
更多高質量乾貨：參見我的 GitHub: dotnetfly
