storage analyze

Author: y123456yz

mongo/mongo.conf

@@ -7,7 +7,7 @@ systemLog:
 storage:
   journal:
     enabled: true
-  dbPath: /home/yangyazhou/backup2
+  dbPath: /home/yangyazhou/backup
   directoryPerDB: true
   engine: wiredTiger
   wiredTiger:

mongo/src/mongo/db/storage/kv/kv_catalog.cpp

@@ -479,6 +479,7 @@ void KVCatalog::init(OperationContext* opCtx) {
         }
 
         // No rollback since this is just loading already committed data.
+        //表及其对应的ident信息
         string ns = obj["ns"].String();
         string ident = obj["ident"].String();
         _idents[ns] = Entry(ident, record->id);
@@ -571,6 +572,10 @@ Status KVCatalog::newCollection(OperationContext* opCtx,
 
 	//更新_idents，记录下集合对应元数据信息，也就是集合路径  集合uuid 集合索引，以及在元数据_mdb_catalog.wt中的位置
     old = Entry(ident, res.getValue());
+	//2021-05-01T11:12:42.394+0800 D STORAGE  [conn-1] stored meta data for test.mycol @ RecordId(6) 
+	//obj:{ ns: "test.mycol", ident: "test/collection/1--6948813758302814892", md: { ns: "test.mycol", 
+	//options: { uuid: UUID("75591c22-bd0f-4a56-ac95-ef90224cf3df"), capped: true, size: 6142976, max: 10000, autoIndexId: true }, 
+	//indexes: [], prefix: -1 } }
 	//集合元数据信息存入_mdb_catalog.wt
     LOG(1) << "stored meta data for " << ns << " @ " << res.getValue() << " obj:" << redact(obj);;
     return Status::OK();
@@ -594,7 +599,7 @@ std::string KVCatalog::getIndexIdent(OperationContext* opCtx,
     return idxIdent[idxName].String();
 }
 
-//_mdb_catalog.wt中查找   KVCatalog::getMetaData中执行
+//_mdb_catalog.wt中查找   下面的KVCatalog::getMetaData中执行
 BSONObj KVCatalog::_findEntry(OperationContext* opCtx, StringData ns, RecordId* out) const {
     RecordId dl;
     {
@@ -626,6 +631,7 @@ BSONObj KVCatalog::_findEntry(OperationContext* opCtx, StringData ns, RecordId*
 //KVStorageEngine::reconcileCatalogAndIdents    KVStorageEngine::KVStorageEngine
 
 //获取MetaData信息，KVCollectionCatalogEntry::_getMetaData调用
+//获取表ns的元数据信息
 const BSONCollectionCatalogEntry::MetaData KVCatalog::getMetaData(OperationContext* opCtx,
                                                                   StringData ns) {
     BSONObj obj = _findEntry(opCtx, ns);
@@ -645,6 +651,8 @@ const BSONCollectionCatalogEntry::MetaData KVCatalog::getMetaData(OperationConte
 
 //KVCollectionCatalogEntry类的如下相关接口完成对MetaData的更新:updateValidator   updateFlags  setIsTemp  removeUUID  addUUID  updateTTLSetting  indexBuildSuccess
 //KVCollectionCatalogEntry类的相关接口调用，完成MetaData相关成员更新
+
+//更新某个表的元数据信息  KVCollectionCatalogEntry类的相关接口调用，完成MetaData相关成员更新
 void KVCatalog::putMetaData(OperationContext* opCtx,
                             StringData ns,
                             BSONCollectionCatalogEntry::MetaData& md) {
@@ -685,11 +693,18 @@ void KVCatalog::putMetaData(OperationContext* opCtx,
 	//{ _id: BinData(0, 00) }, head: 0, prefix: -1 } ], prefix: -1 }, idxIdent: { _id_: "admin/index/1--9034870482849730886" }, 
 	//ns: "admin.system.version", ident: "admin/collection/0--9034870482849730886" }
 
+	//建一个新表的元数据打印:db.createCollection("mycol", { capped : true, autoIndexId : true, size :    6142800, max : 10000 } )
+	//{ md: { ns: "test.mycol", options: { uuid: UUID("75591c22-bd0f-4a56-ac95-ef90224cf3df"), capped: true, size: 6142976, max: 10000, autoIndexId: true }, 
+	//indexes: [ { spec: { v: 2, key: { _id: 1 }, name: "_id_", ns: "test.mycol" }, ready: false, multikey: false, 
+	//multikeyPaths: { _id: BinData(0, 00) }, head: 0, prefix: -1 } ], prefix: -1 }, idxIdent: { _id_: "test/index/2--6948813758302814892" }, 
+	//ns: "test.mycol", ident: "test/collection/1--6948813758302814892" }
+
     LOG(3) << "recording new metadata: " << obj;
     Status status = _rs->updateRecord(opCtx, loc, obj.objdata(), obj.objsize(), false, NULL);
     fassert(28521, status.isOK());
 }
 
+//表重命名后元数据也要更新
 Status KVCatalog::renameCollection(OperationContext* opCtx,
                                    StringData fromNS,
                                    StringData toNS,
@@ -732,6 +747,7 @@ Status KVCatalog::renameCollection(OperationContext* opCtx,
 //drop删表CmdDrop::errmsgRun->dropCollection->DatabaseImpl::dropCollectionEvenIfSystem->DatabaseImpl::_finishDropCollection
 //    ->DatabaseImpl::_finishDropCollection->KVDatabaseCatalogEntryBase::dropCollection->KVCatalog::dropCollection
 //配合KVDatabaseCatalogEntryBase::createCollection->KVCatalog::newCollection阅读
+//删除表后需要从元数据中删除该表
 Status KVCatalog::dropCollection(OperationContext* opCtx, StringData ns) {
     invariant(opCtx->lockState()->isDbLockedForMode(nsToDatabaseSubstring(ns), MODE_X));
     stdx::lock_guard<stdx::mutex> lk(_identsLock);

mongo/src/mongo/db/storage/kv/kv_database_catalog_entry_base.cpp

@@ -409,12 +409,13 @@ Status KVDatabaseCatalogEntryBase::dropCollection(OperationContext* opCtx, Strin
     KVCollectionCatalogEntry* const entry = it->second;
 
     invariant(entry->getTotalIndexCount(opCtx) == entry->getCompletedIndexCount(opCtx));
-
+	//先清除该表的所有索引
     {
         std::vector<std::string> indexNames;
         entry->getAllIndexes(opCtx, &indexNames);
         for (size_t i = 0; i < indexNames.size(); i++) {
 			//KVCollectionCatalogEntry::removeIndex
+			//从该表MetaData元数据中清除该index，并清除索引文件
             entry->removeIndex(opCtx, indexNames[i]).transitional_ignore();
         }
     }
@@ -424,7 +425,8 @@ Status KVDatabaseCatalogEntryBase::dropCollection(OperationContext* opCtx, Strin
     const std::string ident = _engine->getCatalog()->getCollectionIdent(ns);
 
 	//KVStorageEngine::getCatalog获取KVDatabaseCatalogEntry   KVStorageEngine::getCatalog获取KVCatalog
-	//KVCatalog::dropCollection
+	//KVCatalog::dropCollection 
+	//删除表后需要从元数据中删除该表
     Status status = _engine->getCatalog()->dropCollection(opCtx, ns);
     if (!status.isOK()) {
         return status;
@@ -437,6 +439,7 @@ Status KVDatabaseCatalogEntryBase::dropCollection(OperationContext* opCtx, Strin
     //最终外层调用触发RemoveCollectionChange::commit真正进行删除
         new RemoveCollectionChange(opCtx, this, ns, ident, it->second, true));
 
+	//从cache中清除该表
     _collections.erase(ns.toString());
 
     return Status::OK();

mongo/src/mongo/db/storage/record_data.h

@@ -82,6 +82,7 @@ class RecordData {
         return isOwned() ? BSONObj(releaseBuffer()) : BSONObj(_data);
     }
 
+    //打印可以参考KVCatalog::_findEntry
     BSONObj toBson() && {
         return releaseToBson();
     }