Touch command not working properly ?

[Simon T.]

Hey guys, I was wondering if I was the only one having problem with the touch command.

I'm using the shell v2.2.2 and my cluster is a 2.2.1.

It is not totally clear as from where you have to launch the command: mongoS or mongoD. Since I get an error msg when trying to launch it from a mongoS and the word mongod is in bold in the touch documentation. I figure I had to connect directly to mongoD.

What I did:

1. Restart the cluster so the RAM is not filled with mongoDB data.
2. Launch mongostat, resident memory show 88mb
3. Launch the touch command, ex: db.runCommand({touch:"playerProfiles_osload", data:true, index:true})

While still keeping an eye on mongostat, the resident memory is not raising up, I dont see any faults, by looking at MMS I don't see any activity on MMS neither. Basically, nothing have changed.

After that I try a normal db.COLLECTION.find({_id: {$ne: "RANDOM STRING"}}) and I could see the resident memory starting raise.

So guys... where did I failed ?

Simon

[Eliot Horowitz]

You should measure the os page cache.
After the restart, do "free -m"
cached should be small
after a touch, should be much higher.

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[Simon T.]

Before:

             total       used       free     shared    buffers     cached

Mem:        145349     144971        377          0        316     138531

-/+ buffers/cache:       6123     139225

Swap:       190731          3     190728

After:

             total       used       free     shared    buffers     cached

Mem:        145349     144977        372          0        316     138532

-/+ buffers/cache:       6128     139221

Swap:       190731          3     190728

The collection is 2.4GB and indexes are 70mb. It didn't change very much...

[Gianfranco]

This could be that you've reached the maximum amount of resident memory with your device block settings.

Here's a discussion on the readahead:

http://serverfault.com/questions/408100/mongodb-and-datasets-that-dont-fit-in-ram-no-matter-how-hard-you-shove

The best way to find mongodb resident memory increasing is to watch:

db.serverStatus().mem

Regards