Mongodb increased db.currentOp() issue - node.js

Question

My site using mongodb for the chat application. Mongodb queries are getting timed out so i checked the db.currentOp(). Below is the currentOp() and Mongodb details,
637 active operations
750 inactive operations
Other details about mongodb:
Mongo db is running with sharding
I have two databases
a)First database having, two table only
b)Second database having , 5 tables
My questions are, why the current.Op() count got increased suddenly and what are the causes we have to taken care if currentOp() count is increased. Please help me on this and apologies for my bad English.
Below are the sample output of my currentOp()
MongoDB shell version: 1.8.2
> db.currentOp()
{
"inprog" : [
{
"opid" : "msdata1:234234234",
"active" : true,
"lockType" : "read",
"waitingForLock" : false,
"secs_running" : 43534,
"op" : "getmore",
"ns" : "local.oplog.rs",
"query" : {
},
"client_s" : "70.52.078.123:12345",
"desc" : "conn"
},
{
"opid" : "msdata1:2342323423",
"active" : true,
"lockType" : "read",
"waitingForLock" : false,
"secs_running" : 231231,
"op" : "query",
"ns" : "ichat.chatmemberlist",
"query" : {
"count" : "chatmemberlist",
"query" : {
"Mid" : "23423",
"bmid" : "23423"
}
},
"client_s" : "70.52.078.123:12345",
"desc" : "conn"
},
{
"opid" : "msdata1:2342323423",
"active" : false,
"lockType" : "write",
"waitingForLock" : true,
"op" : "update",
"ns" : "?ichat.useravail",
"query" : {
"Mid" : "23423"
},
"client_s" : "70.512.078234.423:12345",
"desc" : "conn"
},
...
...
...

Answer 1

From the limited amount of info, I can see that your queries are just running a really long time: "secs_running" : 231231, means 231 seconds. It's likely that you don't have enough resources available for the type of queries that you are running. That could be that you don't have enough memory, or perhaps too much queries that are acquiring a lock. If you're not on MongoDB 2.0.x yet, then you might want to upgrade to that too as it has vastly improved locking: http://blog.pythonisito.com/2011/12/mongodbs-write-lock.html
I would advice to check the mongodb.log file to see which queries are being slow, then use explain to figure out whether you've indexes on the columns and then either add indexes, or see how you can re-design your schema if that might look like a better solution.