This document discusses MongoDB's oplog and logging operations. It covers: 1. The createOplog function which creates the oplog as a capped collection in the local database. 2. The logOp function which logs operations to the oplog in BSON format with fields like timestamp, operation type, namespace, and operation object. 3. The _logOp and _logOpOld functions which handle actually writing to the oplog, with _logOpOld writing directly to the data file.

1. MongoDB
2011/6/28

2. • @nobu_k
• Preferred Infrastructure (PFI)
• Sedue
• Sedue MongoDB(1.6)
• CT○
• http://slidesha.re/hl8PyL
• MongoDB as Search Engine Repository

3. • oplog
•

4. • MongoDB
• https://github.com/mongodb/mongo/
commits/master/
• 2011/6/26
•2
• pull

5. oplog
•

6. • 2
• createOplog
• logOp
• db/oplog[h,cpp]
•

7. createOplog
• oplog
•

8. createOplog
void createOplog() { > use local
dblock lk; // DB switched to db local
> show collections
// DB. me
const char * ns = "local.oplog.$main"; oplog.$main
pair.sync
slaves
sources
system.indexes
bool rs = !cmdLine._replSet.empty();
if( rs )
ns = rsoplog; // "local.oplog.rs";
// in db/repl/rs_optime.h
NS

9. oplog
Client::Context ctx(ns); // NS
NamespaceDetails * nsd = nsdetails( ns );
if ( nsd ) { // oplog
... ...
... ...
}

10. • oplog
• ReplicaSet
•

11. oplog
• oplog
•
1. oplog
2. BSON NS
• BSON!!
3. oplog

12. •
• Mac
• oplog capped collection

13. createOplog
•
• db/repl.cpp
• db/repl/rs_initialsync.cpp
• db/repl/rs_initiate.cpp
• ReplicaSet
•

14. •
• dblock
• CmdLine
• Context
• DBDirectClient
• NamespaceDetails, nsdetails
•

15. dblock
• DB
• db/concurrency.h
• Deprecated
• writelock
• dbMutex
• scoped_lock
• RAII

16. CmdLine
•
• db/cmdline.[h, cpp]
• boost::program_options
• extern 2
• db/db.cpp //
• client/clientOnly.cpp //

17. Client::Context
•
• NS
• Client
• db/client.[h,cpp]
• RAII
• DB

18. currentClient
• Client
• Thread Local
• boost::thread_specific_ptr<Client>
• cc(), currenctClient, Context::getClient
• DB

19. DBDirectClient
•
• DBClientInterface (client/dbclient.h)
• DBConnector (client/dbclient.h)
• DBClientWithCommands : public DBClientInterface
• DBClientBase : public DBClientWithCommands, public DBConnector
• DBDirectClient : public DBClientBase
• findOne
• c.findOne→DBClientInterface::findOne→DBClientInterface::findN→(virtual
)DBDirectClient::query→DBClientBase::query
• DBClientCursor
•

20. NamespaceDetails
• .ns (1 )
•
• Database
• MongoDataFile
• Record
•

21. nsdetails
• Context NamespaceDetails
• db/pdfile.h
• cc().database()->namespaceIndex->details
• NamespaceIndex
• map<string, NamespaceDetails>
•

22. logOp
•
•

23. oplog
{
ts: • oplog BSON
op:
ns: NS •
o: BSON
o2:
} • o2

24. • i : insert
• u : update
• d : delete
• c : db cmd? userCreateNS?
• db : declares presence of a database
• n : no op ( )
•
• keep alive
•

25. logOp
_logOp
void logOp(const char *opstr, const char *ns,
const BSONObj& obj, BSONObj *patt, bool *b) {
if ( replSettings.master ) {
_logOp(opstr, ns, 0, obj, patt, b);
}
logOpForSharding( opstr , ns , obj , patt );
}

26. _logOp
•
• _logOpOld
• _logOpRS
• etc?
•

27. _logOpOld
•
• Record theDataFileMgr
• fast_oplog_insert!!
• ( mmap
)

28. append_O_Obj
• partial ”o”+
• BSONBuilder
•
• repeatedly ed

29. _logOpRS
•

30. logOp
•
• grep it!

31. • applyOperation_inlock
• pretouch

32. We are hiring !
•
•
•
•
•
•
•
• OSS
•
• (´ ω `)