WiredTiger存储引擎分析

初始化

mongodb中wiredtiger初始化

MONGO_INITIALIZER_WITH_PREREQUISITES(WiredTigerEngineInit, ("SetGlobalEnvironment"))
(InitializerContext* context) {
getGlobalServiceContext()->registerStorageEngine(kWiredTigerEngineName,
new WiredTigerFactory());

return Status::OK();
}

主要的初始化相关处理：

1、storeMongodOptions()：初始化存储引擎相关配置参数。

2、KVStorageEngine类实例初始化时会调用_engine->createRecordStore、_catalog->init(&opCtx);，然后初始化所有已有的collection及对应db。

3、WiredTigerKVEngine中调用如下函数，建立wiredtiger存储引擎的_conn。

wiredtiger_open(path.c_str(), &_eventHandler, config.c_str(), &_conn);

4、WiredTigerKVEngine构造函数中，实例化了wiredtiger存储引擎的_sessionCache。

_sessionCache.reset(new WiredTigerSessionCache(this));

class WiredTigerSessionCache {
... ...
typedef std::vector<WiredTigerSession*> SessionCache;
SessionCache _sessions;
...
}
class WiredTigerSession {
... ...
WiredTigerSession(WT_CONNECTION* conn, uint64_t epoch = 0, uint64_t cursorEpoch = 0);
... ...
typedef std::list<WiredTigerCachedCursor> CursorCache;
WT_SESSION* _session;  // owned
CursorCache _cursors;  // owned
... ...
}

Created with Raphaël 2.1.0db.cppdb.cppwiredtiger_init.cppwiredtiger_init.cppserver_context_d.cppserver_context_d.cppwiredtiger_kv_engine.cppwiredtiger_kv_engine.cppwiredtiger_session_cache.cppwiredtiger_session_cache.cppwiredtiger_size_store.cppwiredtiger_size_store.cppkv_storage_engine.cppkv_storage_engine.cppregisterStorageEngine(const std::string& name,const StorageEngine::Factory* factory)_storageFactories[name] = factory;_initAndListen()initializeGlobalStorageEngine()const StorageEngine::Factory* factory = _storageFactories[storageGlobalParams.engine];... ..._storageEngine = factory->create(storageGlobalParams, *_lockFile);WiredTigerKVEngine* kv = new WiredTigerKVEngine()_sessionCache.reset(new WiredTigerSessionCache(this));_journalFlusher->go();_sizeStorer->fillCache();return new KVStorageEngine(kv, options);

collection初始化流程

1、以mongodb接收到insert命令后的处理为例：

CmdInsert::CmdInsert() : WriteCmd("insert", BatchedCommandRequest::BatchType_Insert) {}

bool WriteCmd::run(...){
... ...
writeBatchExecutor.executeBatch(request, &response);
... ...
}

WriteBatchExecutor::executeBatch() -> WriteBatchExecutor::bulkExecute() -> WriteBatchExecutor::execInserts()
-> WriteBatchExecutor::insertMany() -> insertOne()

static void insertOne(WriteBatchExecutor::ExecInsertsState* state, WriteOpResult* result){
... ...
if (state->lockAndCheck(result)) {
... ...
}

调用lockAndCheck函数，最终会调用Database::createCollection创建并初始化collection。

2、Database::createCollection会调用如下代码创建collection：

... ...
Status status = _dbEntry->createCollection(txn, ns, options, true /*allocateDefaultSpace*/);
Collection* collection = _getOrCreateCollectionInstance(txn, ns);
_collections[ns] = collection;
... ...

其中，KVDatabaseCatalogEntry中createCollection函数会初始化collection相关名字和对应的WT_SESSION。

Status KVDatabaseCatalogEntry::createCollection(OperationContext* txn, StringData ns,
const CollectionOptions& options, bool allocateDefaultSpace)
{
... ...
Status status = _engine->getCatalog()->newCollection(txn, ns, options);
string ident = _engine->getCatalog()->getCollectionIdent(ns);
status = _engine->getEngine()->createRecordStore(txn, ns, ident, options);
RecordStore* rs = _engine->getEngine()->getRecordStore(txn, ns, ident, options);
_collections[ns.toString()] = new KVCollectionCatalogEntry(_engine->getEngine(), _engine->getCatalog(), ns, ident, rs);
... ...
}

1）KVCatalog::newCollection()函数会调用_newUniqueIdent()函数获得collection对应的文件名字（ident），并且，会将collection的ns、ident存储到元数据文件_mdb_catalog中。

元数据文件_mdb_catalog对应的io结构体和btree会在KVStorageEngined的构造函数中初始化完成。

Status status = _engine->createRecordStore(&opCtx, catalogInfo, catalogInfo, CollectionOptions());
_catalogRecordStore.reset( _engine->getRecordStore(&opCtx, catalogInfo, catalogInfo, CollectionOptions()));
_catalog.reset(new KVCatalog(_catalogRecordStore.get(),_supportsDocLocking,
_options.directoryPerDB,_options.directoryForIndexes));
_catalog->init(&opCtx);
//由于每个collection创建时都会存储到元数据文件_mdb_catalog中，
//因此，可以直接从这个文件中得到所有已创建的collection。
_catalog->getAllCollections(&collections);

2）KVDatabaseCatalogEntry::createCollection()函数会调用WiredTigerKVEngine::createRecordStore()函数创建和初始化WT_SESSION结构体。同时会调用__session_create函数创建文件和初始化对应的btree。

3、 WiredTigerKVEngine::createRecordStore()函数会调用WT_SESSION结构体的__session_create函数创建collection对应ident文件和初始化对应的btree。

Status WiredTigerKVEngine::createRecordStore(OperationContext* opCtx, StringData ns,
StringData ident, const CollectionOptions& options) {
... ...
//ident是类似这种形式：collection-0-rand.wt，_uri(ident)返回的是string("table:") + ident.toString();
string uri = _uri(ident);
WT_SESSION* s = session.getSession();
return wtRCToStatus(s->create(s, uri.c_str(), config.c_str()));
}

4、WT_SESSION结构体的__session_create函数会创建collection对应ident文件和初始化对应的btree。其中，uri的格式为table:collection-x-xxxxx。

__session_create(WT_SESSION *wt_session, const char *uri, const char *config) -> __wt_session_create() ->
__wt_schema_create() -> __create_table()

static int __create_table(WT_SESSION_IMPL *session, const char *name, bool exclusive, const char *config){
... ...
if (!exists) {
WT_ERR(__wt_metadata_insert(session, name, tableconf));
WT_ERR(__wt_schema_get_table(session, tablename, strlen(tablename), true, &table));

if (ncolgroups == 0) {
cgsize = strlen("colgroup:") + strlen(tablename) + 1;
WT_ERR(__wt_calloc_def(session, cgsize, &cgname));
snprintf(cgname, cgsize, "colgroup:%s", tablename);
WT_ERR(__create_colgroup(session, cgname, exclusive, config));
}
}
... ...
}

5、如果ncolgroups为0，即配置文件中没有配置colgroup，则会调用__create_colgroup()函数，在该函数中又会调用__wt_schema_create()函数会创建该table对应的source file和初始化对应的btree。

static int __create_colgroup(WT_SESSION_IMPL *session,const char *name, bool exclusive, const char *config) {
... ...
//__wt_schema_colgroup_source会得到file:collection-x-xxxxx.wt的文件名，后面设置到配置文件中source参数中。
WT_ERR(__wt_schema_colgroup_source(session, table, cgname, config, &namebuf));
source = namebuf.data;
WT_ERR(__wt_buf_fmt(session, &confbuf, "source=\"%s\"", source));
... ...
WT_ERR(__wt_schema_create(session, source, sourceconf));  //创建之前得到的source文件名对应文件的io结构体和btree。
... ...
if (!exists) {
WT_ERR(__wt_metadata_insert(session, name, cgconf));
WT_ERR(__wt_schema_open_colgroups(session, table));
}
}

6、__wt_schema_create()函数会调用__create_file()函数实际完成创建table对应的source file文件和初始化对应的btree的功能。

static int __create_file(WT_SESSION_IMPL *session, const char *uri, bool exclusive, const char *config){
/* create、open对应的source文件*/
WT_ERR(__wt_block_manager_create(session, filename, allocsize));
... ...
//__wt_session_get_btree()函数中会调用__wt_conn_btree_open()函数创建对应的btree。
WT_ERR(__wt_session_get_btree(session, uri, NULL, NULL, WT_DHANDLE_EXCLUSIVE));
}

int __wt_conn_btree_open(WT_SESSION_IMPL *session, const char *cfg[], uint32_t flags){
... ...
WT_ERR(__wt_btree_open(session, cfg));
... ...
}

int __wt_btree_open(WT_SESSION_IMPL *session, const char *op_cfg[]){
... ...
// Initialize and configure the WT_BTREE structure
WT_ERR(__btree_conf(session, &ckpt));
//__wt_block_manager_open()函数内部会调用__bm_method_set()函数设置btree->bm结构体(WT_BM)的相关方法。
WT_ERR(__wt_block_manager_open(session, filename, dhandle->cfg, forced_salvage, readonly, btree->allocsize, &btree->bm));
... ...
WT_ERR(bm->checkpoint_load(bm, session, ckpt.raw.data, ckpt.raw.size, root_addr, &root_addr_size, readonly));
if (creation || root_addr_size == 0)
WT_ERR(__btree_tree_open_empty(session, creation));
else {
WT_ERR(__wt_btree_tree_open(session, root_addr, root_addr_size));
if (!F_ISSET(btree, WT_BTREE_REBALANCE)) {
WT_WITH_PAGE_INDEX(session, ret = __btree_preload(session));
if (btree->type != BTREE_ROW)  WT_ERR(__btree_get_last_recno(session));
}
}
}

__btree_tree_open_empty()或者__wt_btree_tree_open()函数会初始化一颗btree，每次分配都是按linux的一个page的大小分配的，__btree_conf()函数里会调用__btree_page_sizes()函数设置btree相关的。

collection的insert流程

1、以insert一个collection为例，当insertOne()函数中创建了collection后，会调用collection的insertDocument函数插入相关文档数据。

static void insertOne(WriteBatchExecutor::ExecInsertsState* state, WriteOpResult* result){
... ...
Status status = state->getCollection()->insertDocument(txn, insertDoc, true);
... ...
}

Status Collection::insertDocument(OperationContext* txn, const DocWriter* doc, bool enforceQuota) {
... ...
StatusWith<RecordId> loc = _recordStore->insertRecord(txn, doc, _enforceQuota(enforceQuota));
... ...
}

_recordStore->insertRecord(xxx)最终会调用如下函数：

Status WiredTigerRecordStore::insertRecords(OperationContext* txn, std::vector<Record>* records, bool enforceQuota) {
... ...
//会先调用__session_open_cursor()函数打开一个cursor，uri是table:collection-x-xxxxx的格式
WiredTigerCursor curwrap(_uri, _tableId, true, txn);
WT_CURSOR* c = curwrap.get();
... ...
for (auto& record : *records) {
c->set_key(c, _makeKey(record.id));
WiredTigerItem value(record.data.data(), record.data.size());
c->set_value(c, value.Get());
int ret = WT_OP_CHECK(c->insert(c));
}
... ...
}

2、__session_open_cursor()函数会获取或打开btree相关结构及初始化WT_CURSOR结构体的相关函数指针成员。

static int __session_open_cursor(WT_SESSION *wt_session, const char *uri, WT_CURSOR *to_dup,
const char *config, WT_CURSOR **cursorp){
... ...
WT_ERR(__session_open_cursor_int(session, uri, NULL, statjoin ? to_dup : NULL, cfg, &cursor));
... ...
}

static int __session_open_cursor_int(WT_SESSION_IMPL *session, const char *uri,
WT_CURSOR *owner, WT_CURSOR *other, const char *cfg[], WT_CURSOR **cursorp){
... ...
WT_RET(__wt_curtable_open(session, uri, owner, cfg, cursorp));
... ...
}

int __wt_curtable_open(WT_SESSION_IMPL *session, const char *uri, WT_CURSOR *owner, const char *cfg[], WT_CURSOR **cursorp){
... ...
if (table->is_simple) {
ret = __wt_open_cursor(session, table->cgroups[0]->source, NULL, cfg, cursorp);
}
... ...
}

int __wt_open_cursor(WT_SESSION_IMPL *session, const char *uri, WT_CURSOR *owner, const char *cfg[], WT_CURSOR **cursorp)
{
return (__session_open_cursor_int(session, uri, owner, NULL, cfg, cursorp));
}

static int __session_open_cursor_int(WT_SESSION_IMPL *session, const char *uri,
WT_CURSOR *owner, WT_CURSOR *other, const char *cfg[], WT_CURSOR **cursorp){
... ...
WT_RET(__wt_curfile_open(session, uri, owner, cfg, cursorp));
... ...
}

int __wt_curfile_open(WT_SESSION_IMPL *session, const char *uri, WT_CURSOR *owner, const char *cfg[], WT_CURSOR **cursorp){
... ...
ret = __wt_session_get_btree_ckpt(session, uri, cfg, flags);
... ...
WT_ERR(__wt_curfile_create(session, owner, cfg, bulk, bitmap, cursorp));
... ...
}

__wt_curfile_create()函数会初始化WT_CURSOR结构体的相关函数指针成员，c->insert(c)调用时即会调用WT_CURSOR结构体中初始化的insert指针成员。

3、c->insert(c)最终会调用__curfile_insert()函数完成内存数据的修改和log文件的写入。

1、第一步会先调用__txn_logrec_init()函数初始化__wt_txn::logrec，然后再插入__wt_txn::logrec中。

__curfile_insert() -> __wt_btcur_insert() -> __cursor_row_modify() -> __wt_row_modify() -> __wt_txn_log_op() -> __txn_op_log()。

2、第一步的操作完成后，会调用WiredTigerRecoveryUnit::_commit()函数执行log日志的提交。

insertOne() -> WriteUnitOfWork::commit() -> WiredTigerRecoveryUnit::commitUnitOfWork() -> WiredTigerRecoveryUnit::_commit() -> WiredTigerRecoveryUnit::_txnClose() -> s->commit_transaction(…) -> __session_commit_transaction() -> __wt_txn_commit() -> __wt_txn_log_commit()函数完成日志写入。

config_def.c文件中wiredtiger_open_all的配置设置了transaction_sync.method会刷入硬盘。

3、wiredtiger_open() -> __wt_connection_workers() -> __wt_logmgr_open()，在函数中会创建线程，执行__log_server()函数，专门执行journal日志的落地。

#define WT_LOG_FILENAME "WiredTigerLog"     /* Log file name */
#define WT_LOG_PREPNAME "WiredTigerPreplog" /* Log pre-allocated name */
#define WT_LOG_TMPNAME  "WiredTigerTmplog"  /* Log temporary name */

cache淘汰

__wt_btcur_insert() -> __cursor_func_init() -> __curfile_enter() -> __cursor_enter() -> __wt_cache_eviction_check() -> __wt_eviction_needed()、__wt_cache_eviction_worker()

MongoDB 3.2.9 请求 hang 分析及 wiredtiger 调优