query not recording (too large)

[Luminosity]

Hello,
We've recently tried using mongo for collecting some traffic
statistics, and it works well for the most part...
However, sometimes db.currentOp(); will tell me something like this:

> db.currentOp();
{
"inprog" : [
{
"opid" : 24685556,
"active" : true,
"lockType" : "write",
"waitingForLock" : false,
"secs_running" : 0,
"op" : "update",
"ns" : "statistics.hits",
"query" : {
"$msg" : "query not recording (too
large)"
},
"client" : "xxx",
"desc" : "conn"
}
]
}


What exactly does that mean - query not recording?
Should I be worried? I'm not seeing any performance issues, just this
weird message.
There seems to be surprisingly little info about this error that I
found on google...

Also, it seems that when rows get deleted from a collection, the index
size doesn't go down, or goes down by very little. Is that something
to worry about as well?

P.S. We're running mongo 1.6 on centOS.

[Eliot Horowitz]

The current operation buffer is 256 bytes. If the query is bigger
than that, it won't store it.

Do you know what the operation is?

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[Luminosity]

Well there are few upserts happening in different places...
We record user agent and http referer strings, so one query can easily
exceed 256 bytes in length.

Does the message simply mean that the query is too big to be displayed
via shell interface?
Or does it mean that the query failed?


P.S. What about index behaviour? Do indexes ever shrink when data is
deleted from collection?
I can't just reindex a live collection because it will lock for like 5
minutes.

[Eliot Horowitz]

It just means its too large to be displayed in the diagnostic views.
We should probably make the buffer a bit bigger.

Indexes will shrink, but we don't shrink aggressively. More so in 1.6 than 1.4