Mongodb源码分析--插入记录及索引B树构建
在之前的一篇文章中，介绍了assembleResponse函数(位于instance.cpp第224行)，它会根据op操作枚举类型来调用相应的crud操作，枚举类型定义如下：
可以看到dbInsert = 2002 为插入操作枚举值，下面我们看一下assembleResponse在确定是插入操作时调用的方法，如下：
从上面代码可以看出，系统在确定dbInsert操作时，调用了receivedInsert()方法（位于instance.cpp文件第570行），下面是该方法的定义：
上面的方法中，主要是在“写锁”环境下执行插入数据操作，并且在插入记录之前进行简单的数据对象检查，如长度和插入数据是否被修改，以确保数据的最终有效性。
最终上面代码会调用 insertWithObjMod()方法（位于pdfile.cpp 文件第1432行），该方法定义如下：
该方法只是一个对插入操作及返回结果的封装，其中ns为数据对象的名空间，o就是要插入的数据对象（BSONObj），god用于标识当前BSONObj对象是否为有效数据（false=有效），这里之所以要传入god这个参数，是因为在接下来的insert方法里同时支持添加名空间(及索引)和插入记录操作（都会不断调用该方法），而在添加名空间时god=true。
下面我们看一下insert方法（pdfile.cpp 第1467行），因为其内容较长，请详见注释：
正如之前所说，该方法会完成添加名空间，添加索引，添加数据记录（memcpy调用）。其中名空间的添加方法addNewNamespaceToCatalog比较简单，下面主要介绍一下索引的创建过程，这里分为了两步：
enum Operations {
opReply = 1, /* reply. responseTo is set. */
dbMsg = 1000, /* generic msg command followed by a string */
dbUpdate = 2001, /* update object */
dbInsert = 2002,
//dbGetByOID = 2003,
dbQuery = 2004,
dbGetMore = 2005,
dbDelete = 2006,
dbKillCursors = 2007
};
opReply = 1, /* reply. responseTo is set. */
dbMsg = 1000, /* generic msg command followed by a string */
dbUpdate = 2001, /* update object */
dbInsert = 2002,
//dbGetByOID = 2003,
dbQuery = 2004,
dbGetMore = 2005,
dbDelete = 2006,
dbKillCursors = 2007
};
可以看到dbInsert = 2002 为插入操作枚举值，下面我们看一下assembleResponse在确定是插入操作时调用的方法，如下：
assembleResponse( Message &m, DbResponse &dbresponse, const SockAddr &client ) {
.....
try {
if ( op == dbInsert ) { //添加记录操作
receivedInsert(m, currentOp);
}
else if ( op == dbUpdate ) { //更新记录
receivedUpdate(m, currentOp);
}
else if ( op == dbDelete ) { //删除记录
receivedDelete(m, currentOp);
}
else if ( op == dbKillCursors ) { //删除Cursors（游标）对象
currentOp.ensureStarted();
logThreshold = 10;
ss << "killcursors ";
receivedKillCursors(m);
}
else {
mongo::log() << " operation isn't supported: " << op << endl;
currentOp.done();
log = true;
}
}
.....
}
}
.....
try {
if ( op == dbInsert ) { //添加记录操作
receivedInsert(m, currentOp);
}
else if ( op == dbUpdate ) { //更新记录
receivedUpdate(m, currentOp);
}
else if ( op == dbDelete ) { //删除记录
receivedDelete(m, currentOp);
}
else if ( op == dbKillCursors ) { //删除Cursors（游标）对象
currentOp.ensureStarted();
logThreshold = 10;
ss << "killcursors ";
receivedKillCursors(m);
}
else {
mongo::log() << " operation isn't supported: " << op << endl;
currentOp.done();
log = true;
}
}
.....
}
}
从上面代码可以看出，系统在确定dbInsert操作时，调用了receivedInsert()方法（位于instance.cpp文件第570行），下面是该方法的定义：
void receivedInsert(Message& m, CurOp& op) {
DbMessage d(m);//初始化数据库格式的消息
const char *ns = d.getns();//获取名空间，用于接下来insert数据
assert(*ns);
uassert( 10058 , "not master", isMasterNs( ns ) );
op.debug().str << ns;
writelock lk(ns);//声明写锁
if ( handlePossibleShardedMessage( m , 0 ) )//查看是不是sharding信息，如果是则处理
return;
Client::Context ctx(ns);
int n = 0;
while ( d.moreJSObjs() ) { //循环获取当前消息体中的BSONObj数据（数据库记录）
BSONObj js = d.nextJsObj();
uassert( 10059 , "object to insert too large", js.objsize() <= BSONObjMaxUserSize);
{
// 声明BSONObj迭代器，以查看里面元素是否有更新操作，如set inc push pull 等
BSONObjIterator i( js );
while ( i.more() ) {
BSONElement e = i.next();
uassert( 13511 , "object to insert can't have $ modifiers" , e.fieldName()[0] != '$' );
}
}
//插入记录操作，god = false用于标识当前BSONObj对象为有效数据
theDataFileMgr.insertWithObjMod(ns, js, false);
logOp("i", ns, js);//日志操作，包括master状态下及sharding分片情况
if( ++n % 4 == 0 ) {
// 在插入一些数据后，进行持久化操作，有关持久化部分参见我的这篇文章
// http://www.cnblogs.com/daizhj/archive/2011/03/21/1990344.html
getDur().commitIfNeeded();
}
}
globalOpCounters.incInsertInWriteLock(n);//在写锁环境下添加已插入记录数（n）,锁采用InterlockedIncrement实现数的原子性
}
DbMessage d(m);//初始化数据库格式的消息
const char *ns = d.getns();//获取名空间，用于接下来insert数据
assert(*ns);
uassert( 10058 , "not master", isMasterNs( ns ) );
op.debug().str << ns;
writelock lk(ns);//声明写锁
if ( handlePossibleShardedMessage( m , 0 ) )//查看是不是sharding信息，如果是则处理
return;
Client::Context ctx(ns);
int n = 0;
while ( d.moreJSObjs() ) { //循环获取当前消息体中的BSONObj数据（数据库记录）
BSONObj js = d.nextJsObj();
uassert( 10059 , "object to insert too large", js.objsize() <= BSONObjMaxUserSize);
{
// 声明BSONObj迭代器，以查看里面元素是否有更新操作，如set inc push pull 等
BSONObjIterator i( js );
while ( i.more() ) {
BSONElement e = i.next();
uassert( 13511 , "object to insert can't have $ modifiers" , e.fieldName()[0] != '$' );
}
}
//插入记录操作，god = false用于标识当前BSONObj对象为有效数据
theDataFileMgr.insertWithObjMod(ns, js, false);
logOp("i", ns, js);//日志操作，包括master状态下及sharding分片情况
if( ++n % 4 == 0 ) {
// 在插入一些数据后，进行持久化操作，有关持久化部分参见我的这篇文章
// http://www.cnblogs.com/daizhj/archive/2011/03/21/1990344.html
getDur().commitIfNeeded();
}
}
globalOpCounters.incInsertInWriteLock(n);//在写锁环境下添加已插入记录数（n）,锁采用InterlockedIncrement实现数的原子性
}
上面的方法中，主要是在“写锁”环境下执行插入数据操作，并且在插入记录之前进行简单的数据对象检查，如长度和插入数据是否被修改，以确保数据的最终有效性。
最终上面代码会调用 insertWithObjMod()方法（位于pdfile.cpp 文件第1432行），该方法定义如下：
DiskLoc DataFileMgr::insertWithObjMod(const char *ns, BSONObj &o, bool god) {
DiskLoc loc = insert( ns, o.objdata(), o.objsize(), god );
if ( !loc.isNull() )//判断返回记录地址是否为空（记录是否插入成功）
o = BSONObj( loc.rec() );//如有效，则用记录地地址上的记录(record类型指针)绑定到o上
return loc;
}
DiskLoc loc = insert( ns, o.objdata(), o.objsize(), god );
if ( !loc.isNull() )//判断返回记录地址是否为空（记录是否插入成功）
o = BSONObj( loc.rec() );//如有效，则用记录地地址上的记录(record类型指针)绑定到o上
return loc;
}
该方法只是一个对插入操作及返回结果的封装，其中ns为数据对象的名空间，o就是要插入的数据对象（BSONObj），god用于标识当前BSONObj对象是否为有效数据（false=有效），这里之所以要传入god这个参数，是因为在接下来的insert方法里同时支持添加名空间(及索引)和插入记录操作（都会不断调用该方法），而在添加名空间时god=true。
下面我们看一下insert方法（pdfile.cpp 第1467行），因为其内容较长，请详见注释：
DiskLoc DataFileMgr::insert(const char *ns, const void *obuf, int len, bool god, const BSONElement &writeId, bool mayAddIndex) {
bool wouldAddIndex = false;
massert( 10093 , "cannot insert into reserved $ collection", god || isANormalNSName( ns ) );
uassert( 10094 , str::stream() << "invalid ns: " << ns , isValidNS( ns ) );
const char *sys = strstr(ns, "system.");
if ( sys ) {//对插入记录的ns进行判断，是否要插入保留的数据库名(system)，如是则停止执行其它代码
uassert( 10095 , "attempt to insert in reserved database name 'system'", sys != ns);
if ( strstr(ns, ".system.") ) {
// later:check for dba-type permissions here if have that at some point separate
if ( strstr(ns, ".system.indexes" ) )//判断是否创建索引
wouldAddIndex = true;
else if ( legalClientSystemNS( ns , true ) )
;
else if ( !god ) {//表示obuf有数据，但这就意味着要向system下插入数据（把system当成数据表了）
out() << "ERROR: attempt to insert in system namespace " << ns << endl;
return DiskLoc();
}
}
else
sys = 0;
}
bool addIndex = wouldAddIndex && mayAddIndex;//判断是否需要添加索引
NamespaceDetails *d = nsdetails(ns);//获取ns的详细信息
if ( d == 0 ) {
addNewNamespaceToCatalog(ns);//向system catalog添加新的名空间，它会再次调用当前insert()方法
/* todo: shouldn't be in the namespace catalog until after the allocations here work.
also if this is an addIndex, those checks should happen before this!
*/
// 创建第一个数据库文件.
cc().database()->allocExtent(ns, Extent::initialSize(len), false);
d = nsdetails(ns);
if ( !god )
ensureIdIndexForNewNs(ns);
}
d->paddingFits();
NamespaceDetails *tableToIndex = 0;
string tabletoidxns;
BSONObj fixedIndexObject;
if ( addIndex ) {
assert( obuf );
BSONObj io((const char *) obuf);
//做索引准备工作，这里并不真正创建索引，只是进行参数检查，以及索引是否已存在等
if( !prepareToBuildIndex(io, god, tabletoidxns, tableToIndex, fixedIndexObject ) )
return DiskLoc();
if ( ! fixedIndexObject.isEmpty() ) {
obuf = fixedIndexObject.objdata();
len = fixedIndexObject.objsize();
}
}
const BSONElement *newId = &writeId;
int addID = 0;
if( !god ) {
//检查对象 是否有_id字段，没有则添加
//Note that btree buckets which we insert aren't BSONObj's, but in that case god==true.
BSONObj io((const char *) obuf);
BSONElement idField = io.getField( "_id" );
uassert( 10099 , "_id cannot be an array", idField.type() != Array );
if( idField.eoo() /*判断是否是结束元素*/&& !wouldAddIndex && strstr(ns, ".local.") == 0 ) {
addID = len;
if ( writeId.eoo() ) {
// 初始化一个_id 随机值（因为_id可能是12 byte类型或其它类型）
idToInsert_.oid.init();
newId = &idToInsert;//绑定初始化的_id值
}
len += newId->size();
}
//如果io对象中有时间戳元素时，并用当前时间进行更新
BSONElementManipulator::lookForTimestamps( io );
}
//兼容旧的数据文件
DiskLoc extentLoc;
int lenWHdr = len + Record::HeaderSize;
lenWHdr = (int) (lenWHdr * d->paddingFactor);
if ( lenWHdr == 0 ) {
assert( d->paddingFactor == 0 );
*getDur().writing(&d->paddingFactor) = 1.0;
lenWHdr = len + Record::HeaderSize;
}
// 在对新的对象分配空间前检查数据是否会造成索引冲突（唯一索引）
// capped标识是否是固定大小的集合类型，这种类型下系统会自动将过于陈旧的数据remove掉
// 注：此cap与nosql中常说的cap无太大关联
// nosql cap即：一致性，有效性，分区容忍性
// 参见这篇文章:http://blog.nosqlfan.com/html/1112.html,
// http://blog.nosqlfan.com/html/96.html)
if ( d->nIndexes && d->capped && !god ) {
checkNoIndexConflicts( d, BSONObj( reinterpret_cast<const char *>( obuf ) ) );
}
DiskLoc loc = d->alloc(ns, lenWHdr, extentLoc);//为当前记录分配空间namespace.cpp __stdAlloc方法
if ( loc.isNull() ) {//如果分配失效
if ( d->capped == 0 ) { // cap大小未增加，即
log(1) << "allocating new extent for " << ns << " padding:" << d->paddingFactor << " lenWHdr: " << lenWHdr << endl;
//尝试从空闲空间列表中分配空间
cc().database()->allocExtent(ns, Extent::followupSize(lenWHdr, d->lastExtentSize), false);
//尝试再次为当前记录分配空间
loc = d->alloc(ns, lenWHdr, extentLoc);
if ( loc.isNull() ) {
log() << "WARNING: alloc() failed after allocating new extent. lenWHdr: " << lenWHdr << " last extent size:" << d->lastExtentSize << "; trying again\n";
for ( int zzz=0; zzz<10 && lenWHdr > d->lastExtentSize; zzz++ ) {//最多尝试循环10次分配空间
log() << "try #" << zzz << endl;
cc().database()->allocExtent(ns, Extent::followupSize(len, d->lastExtentSize), false);
loc = d->alloc(ns, lenWHdr, extentLoc);
if ( ! loc.isNull() )
break;
}
}
}
if ( loc.isNull() ) {//最终未分配空间给对象
log() << "insert: couldn't alloc space for object ns:" << ns << " capped:" << d->capped << endl;
assert(d->capped);
return DiskLoc();
}
}
Record *r = loc.rec();
{
assert( r->lengthWithHeaders >= lenWHdr );
r = (Record*) getDur().writingPtr(r, lenWHdr);//持久化插入记录信息
if( addID ) {
/* a little effort was made here to avoid a double copy when we add an ID */
((int&)*r->data) = *((int*) obuf) + newId->size();
memcpy(r->data+4, newId->rawdata(), newId->size());//拷贝_id字段到指定记录内存空间
memcpy(r->data+4+newId->size(), ((char *)obuf)+4, addID-4);//拷贝数据到指定内存空间
}
else {
if( obuf )
memcpy(r->data, obuf, len);//直接拷贝数据到记录字段r
}
}
{
Extent *e = r->myExtent(loc);
if ( e->lastRecord.isNull() ) {//如果未尾记录为空，本人理解：即之前未插入过记录
Extent::FL *fl = getDur().writing(e->fl());
fl->firstRecord = fl->lastRecord = loc;
r->prevOfs = r->nextOfs = DiskLoc::NullOfs;
}
else {
Record *oldlast = e->lastRecord.rec();//否则将新记录添加到最后一条记录的后面
r->prevOfs = e->lastRecord.getOfs();
r->nextOfs = DiskLoc::NullOfs;
getDur().writingInt(oldlast->nextOfs) = loc.getOfs();
getDur().writingDiskLoc(e->lastRecord) = loc;
}
}
/* 持久化操作并更新相应统计信息 */
{
NamespaceDetails::Stats *s = getDur().writing(&d->stats);
s->datasize += r->netLength();
s->nrecords++;
}
// 在god时会清空stats信息，同时会添加一个 btree bucket（占据存储空间）
if ( !god )
NamespaceDetailsTransient::get_w( ns ).notifyOfWriteOp();//在写操作时清空缓存，优化查询优化
if ( tableToIndex ) {
uassert( 13143 , "can't create index on system.indexes" , tabletoidxns.find( ".system.indexes" ) == string::npos );
BSONObj info = loc.obj();
bool background = info["background"].trueValue();
if( background && cc().isSyncThread() ) {
/* don't do background indexing on slaves. there are nuances. this could be added later but requires more code.*/
log() << "info: indexing in foreground on this replica; was a background index build on the primary" << endl;
background = false;
}
int idxNo = tableToIndex->nIndexes;
IndexDetails& idx = tableToIndex->addIndex(tabletoidxns.c_str(), !background); // 清空临时缓存信息; 同时递增索引数量
getDur().writingDiskLoc(idx.info) = loc;
try {
buildAnIndex(tabletoidxns, tableToIndex, idx, idxNo, background);//创建索引
}
catch( DBException& e ) {
// 保存异常信息，并执行dropIndexes
LastError *le = lastError.get();
int savecode = 0;
string saveerrmsg;
if ( le ) {
savecode = le->code;
saveerrmsg = le->msg;
}
else {
savecode = e.getCode();
saveerrmsg = e.what();
}
//回滚索引操作(drop索引)
string name = idx.indexName();
BSONObjBuilder b;
string errmsg;
bool ok = dropIndexes(tableToIndex, tabletoidxns.c_str(), name.c_str(), errmsg, b, true);
if( !ok ) {
log() << "failed to drop index after a unique key error building it: " << errmsg << ' ' << tabletoidxns << ' ' << name << endl;
}
assert( le && !saveerrmsg.empty() );
raiseError(savecode,saveerrmsg.c_str());
throw;
}
}
/* 将记录数据添加到索引信息（btree）中 */
if ( d->nIndexes ) {
try {
BSONObj obj(r->data);
indexRecord(d, obj, loc);
}
catch( AssertionException& e ) {
// _id index 键值重复
if( tableToIndex || d->capped ) {
massert( 12583, "unexpected index insertion failure on capped collection", !d->capped );
string s = e.toString();
s += " : on addIndex/capped - collection and its index will not match";
uassert_nothrow(s.c_str());
error() << s << endl;
}
else {
// 回滚上述操作
_deleteRecord(d, ns, r, loc);
throw;
}
}
}
// out() << " inserted at loc:" << hex << loc.getOfs() << " lenwhdr:" << hex << lenWHdr << dec << ' ' << ns << endl;
return loc;
}
bool wouldAddIndex = false;
massert( 10093 , "cannot insert into reserved $ collection", god || isANormalNSName( ns ) );
uassert( 10094 , str::stream() << "invalid ns: " << ns , isValidNS( ns ) );
const char *sys = strstr(ns, "system.");
if ( sys ) {//对插入记录的ns进行判断，是否要插入保留的数据库名(system)，如是则停止执行其它代码
uassert( 10095 , "attempt to insert in reserved database name 'system'", sys != ns);
if ( strstr(ns, ".system.") ) {
// later:check for dba-type permissions here if have that at some point separate
if ( strstr(ns, ".system.indexes" ) )//判断是否创建索引
wouldAddIndex = true;
else if ( legalClientSystemNS( ns , true ) )
;
else if ( !god ) {//表示obuf有数据，但这就意味着要向system下插入数据（把system当成数据表了）
out() << "ERROR: attempt to insert in system namespace " << ns << endl;
return DiskLoc();
}
}
else
sys = 0;
}
bool addIndex = wouldAddIndex && mayAddIndex;//判断是否需要添加索引
NamespaceDetails *d = nsdetails(ns);//获取ns的详细信息
if ( d == 0 ) {
addNewNamespaceToCatalog(ns);//向system catalog添加新的名空间，它会再次调用当前insert()方法
/* todo: shouldn't be in the namespace catalog until after the allocations here work.
also if this is an addIndex, those checks should happen before this!
*/
// 创建第一个数据库文件.
cc().database()->allocExtent(ns, Extent::initialSize(len), false);
d = nsdetails(ns);
if ( !god )
ensureIdIndexForNewNs(ns);
}
d->paddingFits();
NamespaceDetails *tableToIndex = 0;
string tabletoidxns;
BSONObj fixedIndexObject;
if ( addIndex ) {
assert( obuf );
BSONObj io((const char *) obuf);
//做索引准备工作，这里并不真正创建索引，只是进行参数检查，以及索引是否已存在等
if( !prepareToBuildIndex(io, god, tabletoidxns, tableToIndex, fixedIndexObject ) )
return DiskLoc();
if ( ! fixedIndexObject.isEmpty() ) {
obuf = fixedIndexObject.objdata();
len = fixedIndexObject.objsize();
}
}
const BSONElement *newId = &writeId;
int addID = 0;
if( !god ) {
//检查对象 是否有_id字段，没有则添加
//Note that btree buckets which we insert aren't BSONObj's, but in that case god==true.
BSONObj io((const char *) obuf);
BSONElement idField = io.getField( "_id" );
uassert( 10099 , "_id cannot be an array", idField.type() != Array );
if( idField.eoo() /*判断是否是结束元素*/&& !wouldAddIndex && strstr(ns, ".local.") == 0 ) {
addID = len;
if ( writeId.eoo() ) {
// 初始化一个_id 随机值（因为_id可能是12 byte类型或其它类型）
idToInsert_.oid.init();
newId = &idToInsert;//绑定初始化的_id值
}
len += newId->size();
}
//如果io对象中有时间戳元素时，并用当前时间进行更新
BSONElementManipulator::lookForTimestamps( io );
}
//兼容旧的数据文件
DiskLoc extentLoc;
int lenWHdr = len + Record::HeaderSize;
lenWHdr = (int) (lenWHdr * d->paddingFactor);
if ( lenWHdr == 0 ) {
assert( d->paddingFactor == 0 );
*getDur().writing(&d->paddingFactor) = 1.0;
lenWHdr = len + Record::HeaderSize;
}
// 在对新的对象分配空间前检查数据是否会造成索引冲突（唯一索引）
// capped标识是否是固定大小的集合类型，这种类型下系统会自动将过于陈旧的数据remove掉
// 注：此cap与nosql中常说的cap无太大关联
// nosql cap即：一致性，有效性，分区容忍性
// 参见这篇文章:http://blog.nosqlfan.com/html/1112.html,
// http://blog.nosqlfan.com/html/96.html)
if ( d->nIndexes && d->capped && !god ) {
checkNoIndexConflicts( d, BSONObj( reinterpret_cast<const char *>( obuf ) ) );
}
DiskLoc loc = d->alloc(ns, lenWHdr, extentLoc);//为当前记录分配空间namespace.cpp __stdAlloc方法
if ( loc.isNull() ) {//如果分配失效
if ( d->capped == 0 ) { // cap大小未增加，即
log(1) << "allocating new extent for " << ns << " padding:" << d->paddingFactor << " lenWHdr: " << lenWHdr << endl;
//尝试从空闲空间列表中分配空间
cc().database()->allocExtent(ns, Extent::followupSize(lenWHdr, d->lastExtentSize), false);
//尝试再次为当前记录分配空间
loc = d->alloc(ns, lenWHdr, extentLoc);
if ( loc.isNull() ) {
log() << "WARNING: alloc() failed after allocating new extent. lenWHdr: " << lenWHdr << " last extent size:" << d->lastExtentSize << "; trying again\n";
for ( int zzz=0; zzz<10 && lenWHdr > d->lastExtentSize; zzz++ ) {//最多尝试循环10次分配空间
log() << "try #" << zzz << endl;
cc().database()->allocExtent(ns, Extent::followupSize(len, d->lastExtentSize), false);
loc = d->alloc(ns, lenWHdr, extentLoc);
if ( ! loc.isNull() )
break;
}
}
}
if ( loc.isNull() ) {//最终未分配空间给对象
log() << "insert: couldn't alloc space for object ns:" << ns << " capped:" << d->capped << endl;
assert(d->capped);
return DiskLoc();
}
}
Record *r = loc.rec();
{
assert( r->lengthWithHeaders >= lenWHdr );
r = (Record*) getDur().writingPtr(r, lenWHdr);//持久化插入记录信息
if( addID ) {
/* a little effort was made here to avoid a double copy when we add an ID */
((int&)*r->data) = *((int*) obuf) + newId->size();
memcpy(r->data+4, newId->rawdata(), newId->size());//拷贝_id字段到指定记录内存空间
memcpy(r->data+4+newId->size(), ((char *)obuf)+4, addID-4);//拷贝数据到指定内存空间
}
else {
if( obuf )
memcpy(r->data, obuf, len);//直接拷贝数据到记录字段r
}
}
{
Extent *e = r->myExtent(loc);
if ( e->lastRecord.isNull() ) {//如果未尾记录为空，本人理解：即之前未插入过记录
Extent::FL *fl = getDur().writing(e->fl());
fl->firstRecord = fl->lastRecord = loc;
r->prevOfs = r->nextOfs = DiskLoc::NullOfs;
}
else {
Record *oldlast = e->lastRecord.rec();//否则将新记录添加到最后一条记录的后面
r->prevOfs = e->lastRecord.getOfs();
r->nextOfs = DiskLoc::NullOfs;
getDur().writingInt(oldlast->nextOfs) = loc.getOfs();
getDur().writingDiskLoc(e->lastRecord) = loc;
}
}
/* 持久化操作并更新相应统计信息 */
{
NamespaceDetails::Stats *s = getDur().writing(&d->stats);
s->datasize += r->netLength();
s->nrecords++;
}
// 在god时会清空stats信息，同时会添加一个 btree bucket（占据存储空间）
if ( !god )
NamespaceDetailsTransient::get_w( ns ).notifyOfWriteOp();//在写操作时清空缓存，优化查询优化
if ( tableToIndex ) {
uassert( 13143 , "can't create index on system.indexes" , tabletoidxns.find( ".system.indexes" ) == string::npos );
BSONObj info = loc.obj();
bool background = info["background"].trueValue();
if( background && cc().isSyncThread() ) {
/* don't do background indexing on slaves. there are nuances. this could be added later but requires more code.*/
log() << "info: indexing in foreground on this replica; was a background index build on the primary" << endl;
background = false;
}
int idxNo = tableToIndex->nIndexes;
IndexDetails& idx = tableToIndex->addIndex(tabletoidxns.c_str(), !background); // 清空临时缓存信息; 同时递增索引数量
getDur().writingDiskLoc(idx.info) = loc;
try {
buildAnIndex(tabletoidxns, tableToIndex, idx, idxNo, background);//创建索引
}
catch( DBException& e ) {
// 保存异常信息，并执行dropIndexes
LastError *le = lastError.get();
int savecode = 0;
string saveerrmsg;
if ( le ) {
savecode = le->code;
saveerrmsg = le->msg;
}
else {
savecode = e.getCode();
saveerrmsg = e.what();
}
//回滚索引操作(drop索引)
string name = idx.indexName();
BSONObjBuilder b;
string errmsg;
bool ok = dropIndexes(tableToIndex, tabletoidxns.c_str(), name.c_str(), errmsg, b, true);
if( !ok ) {
log() << "failed to drop index after a unique key error building it: " << errmsg << ' ' << tabletoidxns << ' ' << name << endl;
}
assert( le && !saveerrmsg.empty() );
raiseError(savecode,saveerrmsg.c_str());
throw;
}
}
/* 将记录数据添加到索引信息（btree）中 */
if ( d->nIndexes ) {
try {
BSONObj obj(r->data);
indexRecord(d, obj, loc);
}
catch( AssertionException& e ) {
// _id index 键值重复
if( tableToIndex || d->capped ) {
massert( 12583, "unexpected index insertion failure on capped collection", !d->capped );
string s = e.toString();
s += " : on addIndex/capped - collection and its index will not match";
uassert_nothrow(s.c_str());
error() << s << endl;
}
else {
// 回滚上述操作
_deleteRecord(d, ns, r, loc);
throw;
}
}
}
// out() << " inserted at loc:" << hex << loc.getOfs() << " lenwhdr:" << hex << lenWHdr << dec << ' ' << ns << endl;
return loc;
}
正如之前所说，该方法会完成添加名空间，添加索引，添加数据记录（memcpy调用）。其中名空间的添加方法addNewNamespaceToCatalog比较简单，下面主要介绍一下索引的创建过程，这里分为了两步：
1.创建索引树（b树）
2.将数据（主要是地址）添加到索引（树）中
先看一下创建索引过程：
static void buildAnIndex(string ns, NamespaceDetails *d, IndexDetails& idx, int idxNo, bool background) {
tlog() << "building new index on " << idx.keyPattern() << " for " << ns << ( background ? " background" : "" ) << endl;
Timer t;
unsigned long long n;
if( background ) {
log(2) << "buildAnIndex: background=true\n";
}
assert( !BackgroundOperation::inProgForNs(ns.c_str()) ); // should have been checked earlier, better not be...
assert( d->indexBuildInProgress == 0 );
assertInWriteLock();
RecoverableIndexState recoverable( d );
if( inDBRepair || !background ) {//当数据库在repair时或非后台工作方式下
n = fastBuildIndex(ns.c_str(), d, idx, idxNo);//创建索引
assert( !idx.head.isNull() );
}
else {
BackgroundIndexBuildJob j(ns.c_str());//以后台方式创建索引
n = j.go(ns, d, idx, idxNo);
}
tlog() << "done for " << n << " records " << t.millis() / 1000.0 << "secs" << endl;
}
tlog() << "building new index on " << idx.keyPattern() << " for " << ns << ( background ? " background" : "" ) << endl;
Timer t;
unsigned long long n;
if( background ) {
log(2) << "buildAnIndex: background=true\n";
}
assert( !BackgroundOperation::inProgForNs(ns.c_str()) ); // should have been checked earlier, better not be...
assert( d->indexBuildInProgress == 0 );
assertInWriteLock();
RecoverableIndexState recoverable( d );
if( inDBRepair || !background ) {//当数据库在repair时或非后台工作方式下
n = fastBuildIndex(ns.c_str(), d, idx, idxNo);//创建索引
assert( !idx.head.isNull() );
}
else {
BackgroundIndexBuildJob j(ns.c_str());//以后台方式创建索引
n = j.go(ns, d, idx, idxNo);
}
tlog() << "done for " << n << " records " << t.millis() / 1000.0 << "secs" << endl;
}
创建索引方法会要据创建方式（是否是后台线程等），使用不同的方法，这里主要讲解非后台方式，也就是上面的fastBuildIndex方法（pdfile.cpp第1101行），其定义如下（内容详见注释）：
unsigned long long fastBuildIndex(const char *ns, NamespaceDetails *d, IndexDetails& idx, int idxNo) {
CurOp * op = cc().curop();//设置当前操作指针，用于设置操作信息
Timer t;
tlog(1) << "fastBuildIndex " << ns << " idxNo:" << idxNo << ' ' << idx.info.obj().toString() << endl;
bool dupsAllowed = !idx.unique();
bool dropDups = idx.dropDups() || inDBRepair;
BSONObj order = idx.keyPattern();
getDur().writingDiskLoc(idx.head).Null();
if ( logLevel > 1 ) printMemInfo( "before index start" );
/* 获取并排序所有键值 ----- */
unsigned long long n = 0;
shared_ptr<Cursor> c = theDataFileMgr.findAll(ns);
BSONObjExternalSorter sorter(order);
sorter.hintNumObjects( d->stats.nrecords );
unsigned long long nkeys = 0;
ProgressMeterHolder pm( op->setMessage( "index: (1/3) external sort" , d->stats.nrecords , 10 ) );
while ( c->ok() ) {
BSONObj o = c->current();
DiskLoc loc = c->currLoc();
BSONObjSetDefaultOrder keys;
idx.getKeysFromObject(o, keys);//从对象中获取键值信息
int k = 0;
for ( BSONObjSetDefaultOrder::iterator i=keys.begin(); i != keys.end(); i++ ) {
if( ++k == 2 ) {//是否是多键索引
d->setIndexIsMultikey(idxNo);
}
sorter.add(*i, loc);//向排序器添加键值和记录位置信息
nkeys++;
}
c->advance();
n++;
pm.hit();
if ( logLevel > 1 && n % 10000 == 0 ) {
printMemInfo( "\t iterating objects" );
}
};
pm.finished();
if ( logLevel > 1 ) printMemInfo( "before final sort" );
sorter.sort();
if ( logLevel > 1 ) printMemInfo( "after final sort" );
log(t.seconds() > 5 ? 0 : 1) << "\t external sort used : " << sorter.numFiles() << " files " << " in " << t.seconds() << " secs" << endl;
list<DiskLoc> dupsToDrop;
/* 创建索引 */
{
BtreeBuilder btBuilder(dupsAllowed, idx);//实例化b树索引对象
//BSONObj keyLast;
auto_ptr<BSONObjExternalSorter::Iterator> i = sorter.iterator();//初始化迭代器用于下面遍历
assert( pm == op->setMessage( "index: (2/3) btree bottom up" , nkeys , 10 ) );
while( i->more() ) {
RARELY killCurrentOp.checkForInterrupt();//检查冲突如shutdown或kill指令
BSONObjExternalSorter::Data d = i->next();
try {
btBuilder.addKey(d.first, d.second);//向b树索引对象中添加索引键值和记录位置信息
}
catch( AssertionException& e ) {
if ( dupsAllowed ) {
// unknow exception??
throw;
}
if( e.interrupted() )
throw;
if ( ! dropDups )
throw;
/* we could queue these on disk, but normally there are very few dups, so instead we
keep in ram and have a limit.
*/
dupsToDrop.push_back(d.second);
uassert( 10092 , "too may dups on index build with dropDups=true", dupsToDrop.size() < 1000000 );
}
pm.hit();
}
pm.finished();
op->setMessage( "index: (3/3) btree-middle" );
log(t.seconds() > 10 ? 0 : 1 ) << "\t done building bottom layer, going to commit" << endl;
btBuilder.commit();//提交创建索引操作，该方法会完成最终构造Btree索引操作
wassert( btBuilder.getn() == nkeys || dropDups );
}
log(1) << "\t fastBuildIndex dupsToDrop:" << dupsToDrop.size() << endl;
//删除索引中已出现的重复记录
for( list<DiskLoc>::iterator i = dupsToDrop.begin(); i != dupsToDrop.end(); i++ )
theDataFileMgr.deleteRecord( ns, i->rec(), *i, false, true );
return n;
}
CurOp * op = cc().curop();//设置当前操作指针，用于设置操作信息
Timer t;
tlog(1) << "fastBuildIndex " << ns << " idxNo:" << idxNo << ' ' << idx.info.obj().toString() << endl;
bool dupsAllowed = !idx.unique();
bool dropDups = idx.dropDups() || inDBRepair;
BSONObj order = idx.keyPattern();
getDur().writingDiskLoc(idx.head).Null();
if ( logLevel > 1 ) printMemInfo( "before index start" );
/* 获取并排序所有键值 ----- */
unsigned long long n = 0;
shared_ptr<Cursor> c = theDataFileMgr.findAll(ns);
BSONObjExternalSorter sorter(order);
sorter.hintNumObjects( d->stats.nrecords );
unsigned long long nkeys = 0;
ProgressMeterHolder pm( op->setMessage( "index: (1/3) external sort" , d->stats.nrecords , 10 ) );
while ( c->ok() ) {
BSONObj o = c->current();
DiskLoc loc = c->currLoc();
BSONObjSetDefaultOrder keys;
idx.getKeysFromObject(o, keys);//从对象中获取键值信息
int k = 0;
for ( BSONObjSetDefaultOrder::iterator i=keys.begin(); i != keys.end(); i++ ) {
if( ++k == 2 ) {//是否是多键索引
d->setIndexIsMultikey(idxNo);
}
sorter.add(*i, loc);//向排序器添加键值和记录位置信息
nkeys++;
}
c->advance();
n++;
pm.hit();
if ( logLevel > 1 && n % 10000 == 0 ) {
printMemInfo( "\t iterating objects" );
}
};
pm.finished();
if ( logLevel > 1 ) printMemInfo( "before final sort" );
sorter.sort();
if ( logLevel > 1 ) printMemInfo( "after final sort" );
log(t.seconds() > 5 ? 0 : 1) << "\t external sort used : " << sorter.numFiles() << " files " << " in " << t.seconds() << " secs" << endl;
list<DiskLoc> dupsToDrop;
/* 创建索引 */
{
BtreeBuilder btBuilder(dupsAllowed, idx);//实例化b树索引对象
//BSONObj keyLast;
auto_ptr<BSONObjExternalSorter::Iterator> i = sorter.iterator();//初始化迭代器用于下面遍历
assert( pm == op->setMessage( "index: (2/3) btree bottom up" , nkeys , 10 ) );
while( i->more() ) {
RARELY killCurrentOp.checkForInterrupt();//检查冲突如shutdown或kill指令
BSONObjExternalSorter::Data d = i->next();
try {
btBuilder.addKey(d.first, d.second);//向b树索引对象中添加索引键值和记录位置信息
}
catch( AssertionException& e ) {
if ( dupsAllowed ) {
// unknow exception??
throw;
}
if( e.interrupted() )
throw;
if ( ! dropDups )
throw;
/* we could queue these on disk, but normally there are very few dups, so instead we
keep in ram and have a limit.
*/
dupsToDrop.push_back(d.second);
uassert( 10092 , "too may dups on index build with dropDups=true", dupsToDrop.size() < 1000000 );
}
pm.hit();
}
pm.finished();
op->setMessage( "index: (3/3) btree-middle" );
log(t.seconds() > 10 ? 0 : 1 ) << "\t done building bottom layer, going to commit" << endl;
btBuilder.commit();//提交创建索引操作，该方法会完成最终构造Btree索引操作
wassert( btBuilder.getn() == nkeys || dropDups );
}
log(1) << "\t fastBuildIndex dupsToDrop:" << dupsToDrop.size() << endl;
//删除索引中已出现的重复记录
for( list<DiskLoc>::iterator i = dupsToDrop.begin(); i != dupsToDrop.end(); i++ )
theDataFileMgr.deleteRecord( ns, i->rec(), *i, false, true );
return n;
}
上面方法主要对要创建的索引信息进行提取，并封装到一个BtreeBuilder中，顾名思义，该对象用于进行b树的创建(因为索引也是一个b树),当信息收集排序完成后，就开始创建索引，如下：
btree.cpp 1842行
void BtreeBuilder::commit() {
buildNextLevel(first);
committed = true;
}
void BtreeBuilder::buildNextLevel(DiskLoc loc) {
int levels = 1;
while( 1 ) {
if( loc.btree()->tempNext().isNull() ) {
// 在当前层级上只有一个 bucket
getDur().writingDiskLoc(idx.head) = loc;
break;
}
levels++;
DiskLoc upLoc = BtreeBucket::addBucket(idx);//添加bucket并实例化上一层DiskLoc
DiskLoc upStart = upLoc;
BtreeBucket *up = upLoc.btreemod();//获取上一层的bucket指针
DiskLoc xloc = loc;
while( !xloc.isNull() ) {
RARELY {
getDur().commitIfNeeded();
b = cur.btreemod();
up = upLoc.btreemod();
}
BtreeBucket *x = xloc.btreemod();
BSONObj k;
DiskLoc r;
x->popBack(r,k);//弹出当前bucket中最右边的键
bool keepX = ( x->n != 0 );//当前bucket中元素个数是否为0
DiskLoc keepLoc = keepX ? xloc : x->nextChild;
//压入上面弹出的最右边的键值，该键值为当前up（bucket）中最大值
if ( ! up->_pushBack(r, k, ordering, keepLoc) )
{
// 当前 bucket 已满，则新创建一个addBucket
DiskLoc n = BtreeBucket::addBucket(idx);
up->tempNext() = n;
upLoc = n;
up = upLoc.btreemod();
up->pushBack(r, k, ordering, keepLoc);
}
DiskLoc nextLoc = x->tempNext(); //get next in chain at current level
if ( keepX ) {//表示当前结点非顶层结点，则设置它的父结点
x->parent = upLoc;
}
else {
if ( !x->nextChild.isNull() )
x->nextChild.btreemod()->parent = upLoc;
x->deallocBucket( xloc, idx );//删除xloc bucket
}
xloc = nextLoc;//指向当前层的下个元素
}
loc = upStart;//升级当前结点
mayCommitProgressDurably();
}
if( levels > 1 )
log(2) << "btree levels: " << levels << endl;
}
void BtreeBuilder::commit() {
buildNextLevel(first);
committed = true;
}
void BtreeBuilder::buildNextLevel(DiskLoc loc) {
int levels = 1;
while( 1 ) {
if( loc.btree()->tempNext().isNull() ) {
// 在当前层级上只有一个 bucket
getDur().writingDiskLoc(idx.head) = loc;
break;
}
levels++;
DiskLoc upLoc = BtreeBucket::addBucket(idx);//添加bucket并实例化上一层DiskLoc
DiskLoc upStart = upLoc;
BtreeBucket *up = upLoc.btreemod();//获取上一层的bucket指针
DiskLoc xloc = loc;
while( !xloc.isNull() ) {
RARELY {
getDur().commitIfNeeded();
b = cur.btreemod();
up = upLoc.btreemod();
}
BtreeBucket *x = xloc.btreemod();
BSONObj k;
DiskLoc r;
x->popBack(r,k);//弹出当前bucket中最右边的键
bool keepX = ( x->n != 0 );//当前bucket中元素个数是否为0
DiskLoc keepLoc = keepX ? xloc : x->nextChild;
//压入上面弹出的最右边的键值，该键值为当前up（bucket）中最大值
if ( ! up->_pushBack(r, k, ordering, keepLoc) )
{
// 当前 bucket 已满，则新创建一个addBucket
DiskLoc n = BtreeBucket::addBucket(idx);
up->tempNext() = n;
upLoc = n;
up = upLoc.btreemod();
up->pushBack(r, k, ordering, keepLoc);
}
DiskLoc nextLoc = x->tempNext(); //get next in chain at current level
if ( keepX ) {//表示当前结点非顶层结点，则设置它的父结点
x->parent = upLoc;
}
else {
if ( !x->nextChild.isNull() )
x->nextChild.btreemod()->parent = upLoc;
x->deallocBucket( xloc, idx );//删除xloc bucket
}
xloc = nextLoc;//指向当前层的下个元素
}
loc = upStart;//升级当前结点
mayCommitProgressDurably();
}
if( levels > 1 )
log(2) << "btree levels: " << levels << endl;
}
上面的buildNextLevel方法自下而上根据之前抽取的键值逐层构造一个b树。这里有一个问题需要注意一下，因为mongodb使用bucket来作为b树中的一个层次结点或叶子结点容器（如下图），bucket最大尺寸为8192字节,c。有关b树索引的文章可以参见这篇文章：，
mongodb目前关于B树索引的文档 ：http://blog.nosqlfan.com/html/758.html
当初始化了b树索引及空间信息之后，下面就会将数据绑定到相应信息结点上了，也就是DataFileMgr::insert方法(pdfile.cpp文件)的如下代码：
/* 将记录数据添加到索引信息（btree）中 */
if ( d->nIndexes ) {
try {
BSONObj obj(r->data);
indexRecord(d, obj, loc);
}
......
}
if ( d->nIndexes ) {
try {
BSONObj obj(r->data);
indexRecord(d, obj, loc);
}
......
}
上面的indexRecord方法会将键值和数据（包括存储位置）添加到索引中(其中参数d包括之前创建的B树索引信息), 该方法定义如下（pdfile.cpp 第1355行）:
/* 将键值和数据（包括存储位置）添加到索引中*/
static void indexRecord(NamespaceDetails *d, BSONObj obj, DiskLoc loc) {
int n = d->nIndexesBeingBuilt();//获取已（及正在）构建的索引数
for ( int i = 0; i < n; i++ ) {
try {
bool unique = d->idx(i).unique();
//内联函数（inline）:将索引和记录相关信息初始化到btree中
_indexRecord(d, i/*索引顺序位*/, obj, loc, /*dupsAllowed*/!unique);
}
catch( DBException& ) {
/* 如果发生异常，则进行回滚操作
note <= i (not < i) is important here as the index we were just attempted
may be multikey and require some cleanup.
*/
for( int j = 0; j <= i; j++ ) {
try {
_unindexRecord(d->idx(j), obj, loc, false);
}
catch(...) {
log(3) << "unindex fails on rollback after unique failure\n";
}
}
throw;
}
}
}
static void indexRecord(NamespaceDetails *d, BSONObj obj, DiskLoc loc) {
int n = d->nIndexesBeingBuilt();//获取已（及正在）构建的索引数
for ( int i = 0; i < n; i++ ) {
try {
bool unique = d->idx(i).unique();
//内联函数（inline）:将索引和记录相关信息初始化到btree中
_indexRecord(d, i/*索引顺序位*/, obj, loc, /*dupsAllowed*/!unique);
}
catch( DBException& ) {
/* 如果发生异常，则进行回滚操作
note <= i (not < i) is important here as the index we were just attempted
may be multikey and require some cleanup.
*/
for( int j = 0; j <= i; j++ ) {
try {
_unindexRecord(d->idx(j), obj, loc, false);
}
catch(...) {
log(3) << "unindex fails on rollback after unique failure\n";
}
}
throw;
}
}
}
上面的_indexRecord为内联函数（pdfile.cpp）（inline关键字参见C++说明），该参数声明如下：
static inline void _indexRecord(NamespaceDetails *d, int idxNo, BSONObj& obj, DiskLoc recordLoc, bool dupsAllowed) {
IndexDetails& idx = d->idx(idxNo);//
BSONObjSetDefaultOrder keys;
idx.getKeysFromObject(obj, keys);//从对象信息中获取键属性信息
BSONObj order = idx.keyPattern();
Ordering ordering = Ordering::make(order);//初始化排序方式用于下面传参
int n = 0;
for ( BSONObjSetDefaultOrder::iterator i=keys.begin(); i != keys.end(); i++ ) {
if( ++n == 2 ) {
d->setIndexIsMultikey(idxNo);//设置多键值索引
}
assert( !recordLoc.isNull() );
try {
idx.head/*DiskLoc*/.btree()/*BtreeBucket*/->bt_insert(idx.head, recordLoc, //执行向btree中添加记录和绑定索引信息的操作
*i, ordering, dupsAllowed, idx);
}
catch (AssertionException& e) {
if( e.getCode() == 10287 && idxNo == d->nIndexes ) {
DEV log() << "info: caught key already in index on bg indexing (ok)" << endl;
continue;
}
if( !dupsAllowed ) {
// 重复键值异常
throw;
}
problem() << " caught assertion _indexRecord " << idx.indexNamespace() << endl;
}
}
}
IndexDetails& idx = d->idx(idxNo);//
BSONObjSetDefaultOrder keys;
idx.getKeysFromObject(obj, keys);//从对象信息中获取键属性信息
BSONObj order = idx.keyPattern();
Ordering ordering = Ordering::make(order);//初始化排序方式用于下面传参
int n = 0;
for ( BSONObjSetDefaultOrder::iterator i=keys.begin(); i != keys.end(); i++ ) {
if( ++n == 2 ) {
d->setIndexIsMultikey(idxNo);//设置多键值索引
}
assert( !recordLoc.isNull() );
try {
idx.head/*DiskLoc*/.btree()/*BtreeBucket*/->bt_insert(idx.head, recordLoc, //执行向btree中添加记录和绑定索引信息的操作
*i, ordering, dupsAllowed, idx);
}
catch (AssertionException& e) {
if( e.getCode() == 10287 && idxNo == d->nIndexes ) {
DEV log() << "info: caught key already in index on bg indexing (ok)" << endl;
continue;
}
if( !dupsAllowed ) {
// 重复键值异常
throw;
}
problem() << " caught assertion _indexRecord " << idx.indexNamespace() << endl;
}
}
}
上面方法最终会执行b树插入方法bt_insert（btree.cpp文件1622行），如下（详情见注释）：
int BtreeBucket::bt_insert(const DiskLoc thisLoc, const DiskLoc recordLoc,
const BSONObj& key, const Ordering &order, bool dupsAllowed,
IndexDetails& idx, bool toplevel) const {
if ( toplevel ) {//如果是顶级节点（如果是通过构造索引方式调用 ，则toplevel=true）
//判断键值是否过界（因为其会存储在system.indexs中），其中：KeyMax = 8192 / 10 .mongodb开发团队可能会在更高版本中扩大该值
if ( key.objsize() > KeyMax ) {
problem() << "Btree::insert: key too large to index, skipping " << idx.indexNamespace() << ' ' << key.objsize() << ' ' << key.toString() << endl;
return 3;
}
}
//执行添加操作
int x = _insert(thisLoc, recordLoc, key, order, dupsAllowed, DiskLoc(), DiskLoc(), idx);
assertValid( order );//assert排序方式是否有效
return x;
}
const BSONObj& key, const Ordering &order, bool dupsAllowed,
IndexDetails& idx, bool toplevel) const {
if ( toplevel ) {//如果是顶级节点（如果是通过构造索引方式调用 ，则toplevel=true）
//判断键值是否过界（因为其会存储在system.indexs中），其中：KeyMax = 8192 / 10 .mongodb开发团队可能会在更高版本中扩大该值
if ( key.objsize() > KeyMax ) {
problem() << "Btree::insert: key too large to index, skipping " << idx.indexNamespace() << ' ' << key.objsize() << ' ' << key.toString() << endl;
return 3;
}
}
//执行添加操作
int x = _insert(thisLoc, recordLoc, key, order, dupsAllowed, DiskLoc(), DiskLoc(), idx);
assertValid( order );//assert排序方式是否有效
return x;
}
上面代码紧接着会调用btree.cpp文件的内部方法_insert（btree.cpp文件 1554行）：
int BtreeBucket::_insert(const DiskLoc thisLoc, const DiskLoc recordLoc,
const BSONObj& key, const Ordering &order, bool dupsAllowed,
const DiskLoc lChild, const DiskLoc rChild, IndexDetails& idx) const {
if ( key.objsize() > KeyMax ) {
problem() << "ERROR: key too large len:" << key.objsize() << " max:" << KeyMax << ' ' << key.objsize() << ' ' << idx.indexNamespace() << endl;
return 2;
}
assert( key.objsize() > 0 );
int pos;
//在btree bucket中使用二分查询，查看键值是否已在所索引信息中
bool found = find(idx, key, recordLoc, order, pos /*返回该索引信息所在或应该在的位置*/, !dupsAllowed);
if ( insert_debug ) {
out() << " " << thisLoc.toString() << '.' << "_insert " <<
key.toString() << '/' << recordLoc.toString() <<
" l:" << lChild.toString() << " r:" << rChild.toString() << endl;
out() << " found:" << found << " pos:" << pos << " n:" << n << endl;
}
if ( found ) {
const _KeyNode& kn = k(pos);//获取指定磁盘位置的节点信息，_KeyNode
if ( kn.isUnused() ) {//查看已存在的键结点是否已使用
log(4) << "btree _insert: reusing unused key" << endl;
massert( 10285 , "_insert: reuse key but lchild is not null", lChild.isNull());
massert( 10286 , "_insert: reuse key but rchild is not null", rChild.isNull());
kn.writing().setUsed();
return 0;
}
DEV {
log() << "_insert(): key already exists in index (ok for background:true)\n";
log() << " " << idx.indexNamespace() << " thisLoc:" << thisLoc.toString() << '\n';
log() << " " << key.toString() << '\n';
log() << " " << "recordLoc:" << recordLoc.toString() << " pos:" << pos << endl;
log() << " old l r: " << childForPos(pos).toString() << ' ' << childForPos(pos+1).toString() << endl;
log() << " new l r: " << lChild.toString() << ' ' << rChild.toString() << endl;
}
alreadyInIndex();//提示键值结点已在索引中，不必再创建，并抛出异常
}
DEBUGGING out() << "TEMP: key: " << key.toString() << endl;
DiskLoc child = childForPos(pos);//查询当前pos的子结点信息，以寻找插入位置
if ( insert_debug )
out() << " getChild(" << pos << "): " << child.toString() << endl;
if ( child.isNull() || !rChild.isNull() /* 在当前buckets中插入，即 'internal' 插入 */ ) {
insertHere(thisLoc, pos, recordLoc, key, order, lChild, rChild, idx);//在当前buckets中插入
return 0;
}
//如果有子结点，则在子结点上执行插入操作
return child.btree()->bt_insert(child, recordLoc, key, order, dupsAllowed, idx, /*toplevel*/false);
}
const BSONObj& key, const Ordering &order, bool dupsAllowed,
const DiskLoc lChild, const DiskLoc rChild, IndexDetails& idx) const {
if ( key.objsize() > KeyMax ) {
problem() << "ERROR: key too large len:" << key.objsize() << " max:" << KeyMax << ' ' << key.objsize() << ' ' << idx.indexNamespace() << endl;
return 2;
}
assert( key.objsize() > 0 );
int pos;
//在btree bucket中使用二分查询，查看键值是否已在所索引信息中
bool found = find(idx, key, recordLoc, order, pos /*返回该索引信息所在或应该在的位置*/, !dupsAllowed);
if ( insert_debug ) {
out() << " " << thisLoc.toString() << '.' << "_insert " <<
key.toString() << '/' << recordLoc.toString() <<
" l:" << lChild.toString() << " r:" << rChild.toString() << endl;
out() << " found:" << found << " pos:" << pos << " n:" << n << endl;
}
if ( found ) {
const _KeyNode& kn = k(pos);//获取指定磁盘位置的节点信息，_KeyNode
if ( kn.isUnused() ) {//查看已存在的键结点是否已使用
log(4) << "btree _insert: reusing unused key" << endl;
massert( 10285 , "_insert: reuse key but lchild is not null", lChild.isNull());
massert( 10286 , "_insert: reuse key but rchild is not null", rChild.isNull());
kn.writing().setUsed();
return 0;
}
DEV {
log() << "_insert(): key already exists in index (ok for background:true)\n";
log() << " " << idx.indexNamespace() << " thisLoc:" << thisLoc.toString() << '\n';
log() << " " << key.toString() << '\n';
log() << " " << "recordLoc:" << recordLoc.toString() << " pos:" << pos << endl;
log() << " old l r: " << childForPos(pos).toString() << ' ' << childForPos(pos+1).toString() << endl;
log() << " new l r: " << lChild.toString() << ' ' << rChild.toString() << endl;
}
alreadyInIndex();//提示键值结点已在索引中，不必再创建，并抛出异常
}
DEBUGGING out() << "TEMP: key: " << key.toString() << endl;
DiskLoc child = childForPos(pos);//查询当前pos的子结点信息，以寻找插入位置
if ( insert_debug )
out() << " getChild(" << pos << "): " << child.toString() << endl;
if ( child.isNull() || !rChild.isNull() /* 在当前buckets中插入，即 'internal' 插入 */ ) {
insertHere(thisLoc, pos, recordLoc, key, order, lChild, rChild, idx);//在当前buckets中插入
return 0;
}
//如果有子结点，则在子结点上执行插入操作
return child.btree()->bt_insert(child, recordLoc, key, order, dupsAllowed, idx, /*toplevel*/false);
}
上面_insert方法首先会使用二分法查找要插入的记录是否已存在于索引中，同时会返回一个插入点（pos），如不存在则会进一步在插入点位置查看找元素以决定是在当前bucket中插入，还是在当前pos位置的（右）子结点(bucket)上插入（这会再次递归调用上面的bt_insert方法），这里我们假定在当前bucket插入，则会执行insertHere方法（btree.cpp文件1183行），它的定义如下：
/**
* insert a key in this bucket, splitting if necessary.
* @keypos - where to insert the key in range 0..n. 0=make leftmost, n=make rightmost.
* NOTE this function may free some data, and as a result the value passed for keypos may
* be invalid after calling insertHere()
*/
void BtreeBucket::insertHere( const DiskLoc thisLoc, int keypos,
const DiskLoc recordLoc, const BSONObj& key, const Ordering& order,
const DiskLoc lchild, const DiskLoc rchild, IndexDetails& idx) const {
if ( insert_debug )
out() << " " << thisLoc.toString() << ".insertHere " << key.toString() << '/' << recordLoc.toString() << ' '
<< lchild.toString() << ' ' << rchild.toString() << " keypos:" << keypos << endl;
DiskLoc oldLoc = thisLoc;
//根据keypos插入相应位置并将数据memcpy到内存指定位置
if ( !basicInsert(thisLoc, keypos, recordLoc, key, order) ) {
//如果插入无效，表示当前bucket已满，则分割记录并放到新创建的bucket中
thisLoc.btreemod()->split(thisLoc, keypos, recordLoc, key, order, lchild, rchild, idx);
return;
}
{//持久化当前thisLoc的结点信息并根据插入位置（是否最后一个key），来更新当前thisLoc（及后面key结点）的子结点信息
const _KeyNode *_kn = &k(keypos);
_KeyNode *kn = (_KeyNode *) getDur().alreadyDeclared((_KeyNode*) _kn); // already declared intent in basicInsert()
if ( keypos+1 == n ) { // n为pack（打包后）存储的记录数，这里"判断等于n"表示为最后(last)一个key
if ( nextChild != lchild ) {//如果是最后元素，那么"当前最高键值的右子结点应该与要插入的左子结点相同
out() << "ERROR nextChild != lchild" << endl;
out() << " thisLoc: " << thisLoc.toString() << ' ' << idx.indexNamespace() << endl;
out() << " keyPos: " << keypos << " n:" << n << endl;
out() << " nextChild: " << nextChild.toString() << " lchild: " << lchild.toString() << endl;
out() << " recordLoc: " << recordLoc.toString() << " rchild: " << rchild.toString() << endl;
out() << " key: " << key.toString() << endl;
dump();
assert(false);
}
kn->prevChildBucket = nextChild;//"当前最高键值的右子结点”绑定到持久化结点的左子结点
assert( kn->prevChildBucket == lchild );
nextChild.writing() = rchild;//持久化"当前最高键值的右子结点”，并将“要插入结点”的右子结点绑定到
if ( !rchild.isNull() )//如果有右子结点，则更新右子结点的父结点信息为当前thisLoc
rchild.btree()->parent.writing() = thisLoc;
}
else {
//如果keypos位置不是最后一个
kn->prevChildBucket = lchild;//将左子结点绑定到keypos位置结点的左子结点上
if ( k(keypos+1).prevChildBucket != lchild ) {//这时左子结点应该与下一个元素的左子结点相同
out() << "ERROR k(keypos+1).prevChildBucket != lchild" << endl;
out() << " thisLoc: " << thisLoc.toString() << ' ' << idx.indexNamespace() << endl;
out() << " keyPos: " << keypos << " n:" << n << endl;
out() << " k(keypos+1).pcb: " << k(keypos+1).prevChildBucket.toString() << " lchild: " << lchild.toString() << endl;
out() << " recordLoc: " << recordLoc.toString() << " rchild: " << rchild.toString() << endl;
out() << " key: " << key.toString() << endl;
dump();
assert(false);
}
const DiskLoc *pc = &k(keypos+1).prevChildBucket;//获取keypos后面元素的左子结点信息
*getDur().alreadyDeclared((DiskLoc*) pc) = rchild; // 将右子结点绑定到下一个元素（keypos+1）的左子结点上declared in basicInsert()
if ( !rchild.isNull() )//如果有右子结点，则更新右子结点的父结点信息为当前thisLoc
rchild.btree()->parent.writing() = thisLoc;
}
return;
}
}
* insert a key in this bucket, splitting if necessary.
* @keypos - where to insert the key in range 0..n. 0=make leftmost, n=make rightmost.
* NOTE this function may free some data, and as a result the value passed for keypos may
* be invalid after calling insertHere()
*/
void BtreeBucket::insertHere( const DiskLoc thisLoc, int keypos,
const DiskLoc recordLoc, const BSONObj& key, const Ordering& order,
const DiskLoc lchild, const DiskLoc rchild, IndexDetails& idx) const {
if ( insert_debug )
out() << " " << thisLoc.toString() << ".insertHere " << key.toString() << '/' << recordLoc.toString() << ' '
<< lchild.toString() << ' ' << rchild.toString() << " keypos:" << keypos << endl;
DiskLoc oldLoc = thisLoc;
//根据keypos插入相应位置并将数据memcpy到内存指定位置
if ( !basicInsert(thisLoc, keypos, recordLoc, key, order) ) {
//如果插入无效，表示当前bucket已满，则分割记录并放到新创建的bucket中
thisLoc.btreemod()->split(thisLoc, keypos, recordLoc, key, order, lchild, rchild, idx);
return;
}
{//持久化当前thisLoc的结点信息并根据插入位置（是否最后一个key），来更新当前thisLoc（及后面key结点）的子结点信息
const _KeyNode *_kn = &k(keypos);
_KeyNode *kn = (_KeyNode *) getDur().alreadyDeclared((_KeyNode*) _kn); // already declared intent in basicInsert()
if ( keypos+1 == n ) { // n为pack（打包后）存储的记录数，这里"判断等于n"表示为最后(last)一个key
if ( nextChild != lchild ) {//如果是最后元素，那么"当前最高键值的右子结点应该与要插入的左子结点相同
out() << "ERROR nextChild != lchild" << endl;
out() << " thisLoc: " << thisLoc.toString() << ' ' << idx.indexNamespace() << endl;
out() << " keyPos: " << keypos << " n:" << n << endl;
out() << " nextChild: " << nextChild.toString() << " lchild: " << lchild.toString() << endl;
out() << " recordLoc: " << recordLoc.toString() << " rchild: " << rchild.toString() << endl;
out() << " key: " << key.toString() << endl;
dump();
assert(false);
}
kn->prevChildBucket = nextChild;//"当前最高键值的右子结点”绑定到持久化结点的左子结点
assert( kn->prevChildBucket == lchild );
nextChild.writing() = rchild;//持久化"当前最高键值的右子结点”，并将“要插入结点”的右子结点绑定到
if ( !rchild.isNull() )//如果有右子结点，则更新右子结点的父结点信息为当前thisLoc
rchild.btree()->parent.writing() = thisLoc;
}
else {
//如果keypos位置不是最后一个
kn->prevChildBucket = lchild;//将左子结点绑定到keypos位置结点的左子结点上
if ( k(keypos+1).prevChildBucket != lchild ) {//这时左子结点应该与下一个元素的左子结点相同
out() << "ERROR k(keypos+1).prevChildBucket != lchild" << endl;
out() << " thisLoc: " << thisLoc.toString() << ' ' << idx.indexNamespace() << endl;
out() << " keyPos: " << keypos << " n:" << n << endl;
out() << " k(keypos+1).pcb: " << k(keypos+1).prevChildBucket.toString() << " lchild: " << lchild.toString() << endl;
out() << " recordLoc: " << recordLoc.toString() << " rchild: " << rchild.toString() << endl;
out() << " key: " << key.toString() << endl;
dump();
assert(false);
}
const DiskLoc *pc = &k(keypos+1).prevChildBucket;//获取keypos后面元素的左子结点信息
*getDur().alreadyDeclared((DiskLoc*) pc) = rchild; // 将右子结点绑定到下一个元素（keypos+1）的左子结点上declared in basicInsert()
if ( !rchild.isNull() )//如果有右子结点，则更新右子结点的父结点信息为当前thisLoc
rchild.btree()->parent.writing() = thisLoc;
}
return;
}
}
该方法中会调用一个叫basicInsert的方法，它主要会在当前bucket中指定位置（keypos）添加记录信息，同时持久化该结点信息，如下：
//tree.cpp 1183
bool BucketBasics::basicInsert(const DiskLoc thisLoc, int &keypos, const DiskLoc recordLoc, const BSONObj& key, const Ordering &order) const {
assert( keypos >= 0 && keypos <= n );
//判断bucket剩余的空间是否满足当前数据需要的存储空间
int bytesNeeded = key.objsize() + sizeof(_KeyNode);
if ( bytesNeeded > emptySize ) {
_pack(thisLoc, order, keypos);//如不够用，进行一次整理打包操作，以为bucket中整理更多空间
if ( bytesNeeded > emptySize )//如还不够用，则返回
return false;
}
BucketBasics *b;//声明Bucket管理对象指针，该对象提供了Bucket存储管理的基本操作和属性，如insert,_pack等
{
const char *p = (const char *) &k(keypos);
const char *q = (const char *) &k(n+1);
// declare that we will write to [k(keypos),k(n)]
// todo: this writes a medium amount to the journal. we may want to add a verb "shift" to the redo log so
// we can log a very small amount.
b = (BucketBasics*) getDur().writingAtOffset((void *) this, p-(char*)this, q-p);
//如已有3个结点，目前要插到第三个结点之间，则对每三个元素进行迁移，
// e.g. n==3, keypos==2
// 1 4 9
// ->
// 1 4 _ 9
for ( int j = n; j > keypos; j-- ) // make room
b->k(j) = b->k(j-1);
}
getDur().declareWriteIntent(&b->emptySize, 12); // [b->emptySize..b->n] is 12 bytes and we are going to write those
b->emptySize -= sizeof(_KeyNode);//将当前bucket中的剩余空闲空间减少
b->n++;//已有结点数加1
_KeyNode& kn = b->k(keypos);
kn.prevChildBucket.Null();//设置当前结点的左子结点为空
kn.recordLoc = recordLoc;//绑定结点记录信息
kn.setKeyDataOfs((short) b->_alloc(key.objsize()) );//设置结点数据偏移信息
char *p = b->dataAt(kn.keyDataOfs());//实例化指向磁盘数据(journal文件)位置（含偏移量）的指针
getDur().declareWriteIntent(p, key.objsize());//持久化结点数据信息
memcpy(p, key.objdata(), key.objsize());//将当前结点信息复制到p指向的地址空间
return true;
}
bool BucketBasics::basicInsert(const DiskLoc thisLoc, int &keypos, const DiskLoc recordLoc, const BSONObj& key, const Ordering &order) const {
assert( keypos >= 0 && keypos <= n );
//判断bucket剩余的空间是否满足当前数据需要的存储空间
int bytesNeeded = key.objsize() + sizeof(_KeyNode);
if ( bytesNeeded > emptySize ) {
_pack(thisLoc, order, keypos);//如不够用，进行一次整理打包操作，以为bucket中整理更多空间
if ( bytesNeeded > emptySize )//如还不够用，则返回
return false;
}
BucketBasics *b;//声明Bucket管理对象指针，该对象提供了Bucket存储管理的基本操作和属性，如insert,_pack等
{
const char *p = (const char *) &k(keypos);
const char *q = (const char *) &k(n+1);
// declare that we will write to [k(keypos),k(n)]
// todo: this writes a medium amount to the journal. we may want to add a verb "shift" to the redo log so
// we can log a very small amount.
b = (BucketBasics*) getDur().writingAtOffset((void *) this, p-(char*)this, q-p);
//如已有3个结点，目前要插到第三个结点之间，则对每三个元素进行迁移，
// e.g. n==3, keypos==2
// 1 4 9
// ->
// 1 4 _ 9
for ( int j = n; j > keypos; j-- ) // make room
b->k(j) = b->k(j-1);
}
getDur().declareWriteIntent(&b->emptySize, 12); // [b->emptySize..b->n] is 12 bytes and we are going to write those
b->emptySize -= sizeof(_KeyNode);//将当前bucket中的剩余空闲空间减少
b->n++;//已有结点数加1
_KeyNode& kn = b->k(keypos);
kn.prevChildBucket.Null();//设置当前结点的左子结点为空
kn.recordLoc = recordLoc;//绑定结点记录信息
kn.setKeyDataOfs((short) b->_alloc(key.objsize()) );//设置结点数据偏移信息
char *p = b->dataAt(kn.keyDataOfs());//实例化指向磁盘数据(journal文件)位置（含偏移量）的指针
getDur().declareWriteIntent(p, key.objsize());//持久化结点数据信息
memcpy(p, key.objdata(), key.objsize());//将当前结点信息复制到p指向的地址空间
return true;
}
如果上面方法调用失效，则意味着当前 bucket中已有可用空间插入新记录，这时系统会调用 split（btree.cpp文件 1240行）方法来进行bucket分割，以创建新的bucket并将信息塞入其中，如下：
void BtreeBucket::split(const DiskLoc thisLoc, int keypos, const DiskLoc recordLoc, const BSONObj& key, const Ordering& order, const DiskLoc lchild, const DiskLoc rchild, IndexDetails& idx) {
assertWritable();
if ( split_debug )
out() << " " << thisLoc.toString() << ".split" << endl;
int split = splitPos( keypos );//找到要迁移的数据位置
DiskLoc rLoc = addBucket(idx);//添加一个新的BtreeBucket
BtreeBucket *r = rLoc.btreemod();
if ( split_debug )
out() << " split:" << split << ' ' << keyNode(split).key.toString() << " n:" << n << endl;
for ( int i = split+1; i < n; i++ ) {
KeyNode kn = keyNode(i);
r->pushBack(kn.recordLoc, kn.key, order, kn.prevChildBucket);//向新bucket中迁移过剩数据
}
r->nextChild = nextChild;//绑定新bucket的右子结点
r->assertValid( order );
if ( split_debug )
out() << " new rLoc:" << rLoc.toString() << endl;
r = 0;
rLoc.btree()->fixParentPtrs(rLoc);//设置当前bucket树的父指针信息
{
KeyNode splitkey = keyNode(split);//获取内存中分割点位置所存储的数据
nextChild = splitkey.prevChildBucket; // 提升splitkey 键，它的子结点将会是 thisLoc (l) 和 rLoc (r)
if ( split_debug ) {
out() << " splitkey key:" << splitkey.key.toString() << endl;
}
// 将 splitkey 提升为父结点
if ( parent.isNull() ) {
// 如果无父结点时，则创建一个，并将
DiskLoc L = addBucket(idx);
BtreeBucket *p = L.btreemod();
p->pushBack(splitkey.recordLoc, splitkey.key, order, thisLoc);
p->nextChild = rLoc;//将分割的bucket为了当前
p->assertValid( order );
parent = idx.head.writing() = L;//将splitkey 提升为父结点
if ( split_debug )
out() << " we were root, making new root:" << hex << parent.getOfs() << dec << endl;
rLoc.btree()->parent.writing() = parent;
}
else {
// set this before calling _insert - if it splits it will do fixParent() logic and change the value.
rLoc.btree()->parent.writing() = parent;
if ( split_debug )
out() << " promoting splitkey key " << splitkey.key.toString() << endl;
//提升splitkey键，它的左子结点 thisLoc， 右子点rLoc
parent.btree()->_insert(parent, splitkey.recordLoc, splitkey.key, order, /*dupsallowed*/true, thisLoc, rLoc, idx);
}
}
int newpos = keypos;
// 打包压缩数据(pack,移除无用数据)，以提供更多空间
truncateTo(split, order, newpos); // note this may trash splitkey.key. thus we had to promote it before finishing up here.
// add our new key, there is room now
{
if ( keypos <= split ) {//如果还有空间存储新键
if ( split_debug )
out() << " keypos<split, insertHere() the new key" << endl;
insertHere(thisLoc, newpos, recordLoc, key, order, lchild, rchild, idx);//再次向当前bucket中添加记录
}
else {//如压缩之后依旧无可用空间，则向新创建的bucket中添加节点
int kp = keypos-split-1;
assert(kp>=0);
rLoc.btree()->insertHere(rLoc, kp, recordLoc, key, order, lchild, rchild, idx);
}
}
if ( split_debug )
out() << " split end " << hex << thisLoc.getOfs() << dec << endl;
}
assertWritable();
if ( split_debug )
out() << " " << thisLoc.toString() << ".split" << endl;
int split = splitPos( keypos );//找到要迁移的数据位置
DiskLoc rLoc = addBucket(idx);//添加一个新的BtreeBucket
BtreeBucket *r = rLoc.btreemod();
if ( split_debug )
out() << " split:" << split << ' ' << keyNode(split).key.toString() << " n:" << n << endl;
for ( int i = split+1; i < n; i++ ) {
KeyNode kn = keyNode(i);
r->pushBack(kn.recordLoc, kn.key, order, kn.prevChildBucket);//向新bucket中迁移过剩数据
}
r->nextChild = nextChild;//绑定新bucket的右子结点
r->assertValid( order );
if ( split_debug )
out() << " new rLoc:" << rLoc.toString() << endl;
r = 0;
rLoc.btree()->fixParentPtrs(rLoc);//设置当前bucket树的父指针信息
{
KeyNode splitkey = keyNode(split);//获取内存中分割点位置所存储的数据
nextChild = splitkey.prevChildBucket; // 提升splitkey 键，它的子结点将会是 thisLoc (l) 和 rLoc (r)
if ( split_debug ) {
out() << " splitkey key:" << splitkey.key.toString() << endl;
}
// 将 splitkey 提升为父结点
if ( parent.isNull() ) {
// 如果无父结点时，则创建一个，并将
DiskLoc L = addBucket(idx);
BtreeBucket *p = L.btreemod();
p->pushBack(splitkey.recordLoc, splitkey.key, order, thisLoc);
p->nextChild = rLoc;//将分割的bucket为了当前
p->assertValid( order );
parent = idx.head.writing() = L;//将splitkey 提升为父结点
if ( split_debug )
out() << " we were root, making new root:" << hex << parent.getOfs() << dec << endl;
rLoc.btree()->parent.writing() = parent;
}
else {
// set this before calling _insert - if it splits it will do fixParent() logic and change the value.
rLoc.btree()->parent.writing() = parent;
if ( split_debug )
out() << " promoting splitkey key " << splitkey.key.toString() << endl;
//提升splitkey键，它的左子结点 thisLoc， 右子点rLoc
parent.btree()->_insert(parent, splitkey.recordLoc, splitkey.key, order, /*dupsallowed*/true, thisLoc, rLoc, idx);
}
}
int newpos = keypos;
// 打包压缩数据(pack,移除无用数据)，以提供更多空间
truncateTo(split, order, newpos); // note this may trash splitkey.key. thus we had to promote it before finishing up here.
// add our new key, there is room now
{
if ( keypos <= split ) {//如果还有空间存储新键
if ( split_debug )
out() << " keypos<split, insertHere() the new key" << endl;
insertHere(thisLoc, newpos, recordLoc, key, order, lchild, rchild, idx);//再次向当前bucket中添加记录
}
else {//如压缩之后依旧无可用空间，则向新创建的bucket中添加节点
int kp = keypos-split-1;
assert(kp>=0);
rLoc.btree()->insertHere(rLoc, kp, recordLoc, key, order, lchild, rchild, idx);
}
}
if ( split_debug )
out() << " split end " << hex << thisLoc.getOfs() << dec << endl;
}
好了，今天的内容到这里就告一段落了，在接下来的文章中，将会介绍客户端发起Delete操作时，Mongodb的执行流程和相应实现部分。
原文链接:http://www.cnblogs.com/daizhj/archive/2011/03/30/1999699.html
作者: daizhj, 代震军
微博: http://t.sina.com.cn/daizhj
Tags: mongodb,c++,btree
