The document provides tips and explanations for various MongoDB commands and operations including explain, hint, setProfilingLevel, currentOp, and mongostat. It discusses using indexes to optimize queries, setting profiling levels to log slow queries, using currentOp to view currently running operations, and using mongostat to view MongoDB server statistics.

1. MongoDB
id:matsuou1

2. !
!
!
!
!
! Tips
!

3. ! ID matsuou1
!
!
!
!
! Oracle PostgreSQL
! MongoDB Hadoop R

4. 1.
2.
3.
4.

6. !
! RDBMS
!

7. !
!

8. MongoDB
!
! CPU
!
! JOIN
!

9. •
• 100 insert update delete
•
• nscanned 10
•

10. db/queryoptimizer.cpp

12. ! explain
> db.logs.find({uid:"a10Sty5jqqiyxxxx2"}).explain();
{
"cursor" : "BasicCursor",
"nscanned" : 2669511,
"nscannedObjects" : 2669511,
"n" : 3,
"millis" : 6100,
"nYields" : 0,
"nChunkSkips" : 0,
"isMultiKey" : false,
"indexOnly" : false,
"indexBounds" : {
}
}

13. cursor
BasicCursor
BasicCursor or BtreeCursor
nscanned
14
nscannedObjects
14
n
14
millis
9
ms
nYields
0
nChunkSkips
0
Chunk
isMultiKey
false
indexOnly
false
indexBounds
scanAndOrder
allPlans

14. ( )
> db.logs.find({uid:"a10Sty5jqqiyxxxx2"}).explain();
{
"cursor" : "BasicCursor",
"nscanned" : 2669511,
"nscannedObjects" : 2669511,
"n" : 3,
"millis" : 6100,
"nYields" : 0, 6100ms
"nChunkSkips" : 0, 3 266
"isMultiKey" : false,
"indexOnly" : false,
"indexBounds" : {
}
}

15. ( )
> db.logs.find({uid:"b3iVxMGIEc3xxxxY"}).explain();
{
"cursor" : "BtreeCursor uid_1",
"nscanned" : 3,
"nscannedObjects" : 3,
"n" : 3,
"millis" : 6,
”uid_1”
"nYields" : 0, 6ms
"nChunkSkips" : 0,
3 3
"isMultiKey" : false,
"indexOnly" : false,
"indexBounds" : {
"uid" : [
[
"b3iVxMGIEc3xxxxY",
"b3iVxMGIEc3xxxxY"
]
]
}
}

17. !
! slowms
!
! db.setProfilingLevel(level,slowms)
!

18. slowms
! mongod slowms
ms
mongod
mongod --logpath=/var/log/mongodb/mongodb.log --logappend –slowms 500
Sat May 14 02:25:53 [conn16] query logdb.$cmd ntoreturn:1
command: { count: "logs", query: { path: "/index.html" }, fields: {} } reslen:64 3116ms

19. setProfilingLevel
setProfilingLevel
(level,slowms)
> db.setProfilingLevel(1,500);
{ "was" : 1, "slowms" : 100, "ok" : 1 }
100ms

20. setProfilingLevel
system.profile
> db.system.profile.find();
{ "ts" : ISODate("2011-05-01T03:40:04.462Z"), "info" : "query logdb.logs reslen:192
nscanned:2669511 nquery: { uid: "b2kwyYCXn3b5Scpr" } nreturned:1 6686ms",
"millis" : 6686 }
ts
millis
info
query
query
query
nscanned
reslen
nreturned

21. db.currentOp
opid
ID KillOp
op
query update
ns
query
lockType
waitingForLock
client
desc

22. > db.currentOp();
{
"inprog" : [
{
"opid" : 272,
"active" : true,
"lockType" : "read",
"waitingForLock" : false,
"secs_running" : 20,
"op" : "query",
"ns" : "logdb.logs",
"query" : {
"count" : "logs",
"query" : {
"month" : "2010/02"
},
"fields" : {
}
},
"client" : "127.0.0.1:59394",
"desc" : "conn"
}]}

23. slowms
db.setProfilingLevel
collection system.profile capped collection
db.currentOp
MongoDB

24. Tips

25. !
• db.c.find( {x:10,y:20} ), using index {x:1,y:1}
• db.c.find( {x:10,y:20} ), using index {x:1,y:-1}
• db.c.find( {x:{$in:[10,20]},y:20} ), using index {x:1,y:1}
• db.c.find().sort( {x:1,y:1} ), using index {x:1,y:1}
• db.c.find().sort( {x:-1,y:1} ), using index {x:1,y:-1}
• db.c.find( {x:10} ).sort( {y:1} ), using index {x: 1,y:1}

26. hint
! hint
!

27. hint
> db.logs.find({uid:"f2RNwtj34m3xxxxB" , path : "/index.html"}).hint({uid:1}).explain();
{
"cursor" : "BtreeCursor uid_1",
"nscanned" : 95,
"nscannedObjects" : 95,
"n" : 35,
"millis" : 3,
"nYields" : 0,
"nChunkSkips" : 0,
"isMultiKey" : false,
"indexOnly" : false,
"indexBounds" : {
"uid" : [
[
"f2RNwtj34m3xxxxB",
"f2RNwtj34m3xxxxB"
]
]
}
}

28. hint
> db.logs.find({uid:"f2RNwtj34m3xxxxB" , path : "/index.html"}).hint({uid:1 , path:1}).explain();
{
"cursor" : "BtreeCursor uid_1_path_1",
"nscanned" : 35,
"nscannedObjects" : 35,
"n" : 35,
"millis" : 0,
"nYields" : 0,
"nChunkSkips" : 0,
"isMultiKey" : false,
"indexOnly" : false,
"indexBounds" : {
"uid" : [
[
"f2RNwtj34m3xxxxB",
"f2RNwtj34m3xxxxB"
]
],
( )
}
}

29. mongostat
mongostat

30. mongostat
inserts
insert /
query
query /
update
update /
delete
delete /
getmore
getmore /
command
command /
flushes
fsync flush /
mapped
Map MB
visze
MB
res
MB
faults
/
locked
Idx miss
qr|qw
read | write
ar|aw
read | write
netIn
In bits
netOut
Out bits
conn

31. collection
! getIndexKeys()
> db.logs.getIndexKeys();
[ { "_id" : 1 }, { "uid" : 1 }, { "uid" : 1, "path" : 1 } ]

32. ! db.currentOp opid db.killOp(opid)
> db.currentOp();
{
"inprog" : [
{
"opid" : 308,
"active" : true,
"lockType" : "read",
"waitingForLock" : false,
"secs_running" : 11,
"op" : "query",
"ns" : "logdb.logs",
( )
}
]
}
> db.killOp(308);
{ "info" : "attempting to kill op" }

33. !
!
! explain
!
! slowms
! setProfilingLevel
! db.currentOP
! Tips
!
! Hint
! mongostat