Question

I’m running a MongoDB instance using a Replica Set, when there are a lot of insert, I can see very weird statistics on faults and locked %.

• How come locked % can be more than 100 ?!

• Where does the faults happen, I have no logs mentioning any fault, does someone have any clue about what it means ?

  insert  query update delete getmore command flushes mapped  vsize    res faults locked % idx miss %     qr|qw   ar|aw  netIn netOut  conn      set repl       time 
   9      0      0      0       1       4       0  70.3g   141g  4.77g     20      124          0       0|0     0|1     1m     2m    10 socialdb    M   18:49:49 
  18      0      0      0       3       1       0  70.3g   141g  4.77g     17     73.8          0       0|0     0|1     1m     2m    10 socialdb    M   18:49:50 
  21      0      0      0       1       5       0  70.3g   141g  4.77g     18      104          0       0|0     0|1     1m     1m    10 socialdb    M   18:49:51 
  20      0      0      0       3       1       0  70.3g   141g  4.78g     18     98.8          0       0|0     0|1     1m     3m    10 socialdb    M   18:49:52 
  172      0      0      0       5       4       0  70.3g   141g  4.79g    133     72.8          0       0|0     0|0     7m    12m    10 socialdb    M   18:49:53 
  76      0      0      0       3       1       0  70.3g   141g   4.8g    114     65.1          0       0|0     0|1     6m    10m    10 socialdb    M   18:49:54 
  54      0      0      0       4       4       1  70.3g   141g  4.81g     45     90.6          0       0|0     0|1     2m     8m    10 socialdb    M   18:49:55 
  85      0      0      0       4       2       0  70.3g   141g  4.84g    101     98.1          0       0|0     0|1     6m    11m    10 socialdb    M   18:49:56 
  77      0      0      0       3       4       0  70.3g   141g  4.82g     78     74.5          0       0|0     0|1     4m     9m    10 socialdb    M   18:49:57 
  72      0      0      0       3       1       0  70.3g   141g  4.84g    111     95.7          0       0|0     0|1     6m    10m    10 socialdb    M   18:49:58 
  

• Is there a better (standard) monitoring tool, free ?

Answer 1

Not sure about the other two but this could be the answer to your first question, if you are using v2.2:
http://docs.mongodb.org/manual/reference/mongostat/
The above page mentions:

locked:
The percent of time in a global write lock.

(Changed in version 2.2: The locked db field replaces the locked % field to more appropriate data regarding the database specific locks in version 2.2)

locked db:
New in version 2.2.

The percent of time in the per-database context-specific lock. mongostat will report the database that has spent the most time since the last mongostat call with a write lock.

This value represents the amount of time the database had a database specific lock and the time that the mongod spent in the global lock. Because of this, and the sampling method, you may see some values greater than 100%.