Strange performance test results with various write problems in MongoDB + C #

Question

Strange performance test results with various write problems in MongoDB + C #

I am trying to check MongoDB performance before using it. I am trying to see how many documents I can update per second. I am using C # (Mono + Ubuntu) MongoDB Driver v1.9 and MongoDB v2.4.6.

I believe that one of the most efficient MongoDB options for write performance is Write Concern. As stated in the documentation , the most laid-back value for anxiety for writing would be -1, then, 0and finally, 1the slowest.

After searching, I found that I could fix write problems in C # built into the connection string, like this:

var client = new MongoClient("mongodb://localhost/?w=-1");

Here are the results that I play with different values for w:

The fastest results are achieved when I install win 1!
Setup is w=0slower than w=128 times!
w=-1will result in an exception being sent with an error message W value must be greater than or equal to zero!

Does anyone have an explanation for these results? Am I doing something wrong?

[UPDATE]

I think it is necessary to establish a testing procedure, maybe there is something hidden there. So here it is:

I have a database with 100M documents in one collection. Each document is created this way using the mongo shell:

{ "counter" : 0, "last_update" : new Date() }

Here's the conclusion db.collection.stats();:

{
    "ns" : "test.collection",
    "count" : 100000100,
    "size" : 6400006560,
    "avgObjSize" : 64.0000015999984,
    "storageSize" : 8683839472,
    "numExtents" : 27,
    "nindexes" : 2,
    "lastExtentSize" : 2146426864,
    "paddingFactor" : 1,
    "systemFlags" : 1,
    "userFlags" : 0,
    "totalIndexSize" : 5769582448,
    "indexSizes" : {
        "_id_" : 3251652432,
        "last_update_1" : 2517930016
    },
    "ok" : 1
}

3.2.1 Ubuntu 12.04 #, MongoDB :

FindAndModifyArgs args = new FindAndModifyArgs();
args.SortBy = SortBy.Ascending("last_update");
args.Update = Update<Entity>.Set(e => e.last_update, DateTime.Now);
args.Fields = Fields.Include(new string[] { "counter", "_id" });
var m = collection.FindAndModify(args);

Entity ent = m.GetModifiedDocumentAs<Entity>();
var query = Query<Entity>.EQ(e => e.Id, ent.Id);
var update = Update<Entity>.Set(e => e.counter, ent.counter+1);
collection.Update(query, update);

, ; last_update, last_update, ( ).

10k Write Concerns, w=-1, w=0, w=1 w=1&j=true. w=-1 , :

, :

            w=-1    w=0                 w=1                 w=1&j=true
Average     N/A     244.0948611492      7064.5143923477     238.1846428156
STDEV       N/A     1.7787457992        511.892765742       21.0230097306

: - , w=0 , w=1 w=-1 ?

[]

RequestStart :

using (server.RequestStart(database)) {
    FindAndModifyArgs args = new FindAndModifyArgs();
    args.SortBy = SortBy.Ascending("last_update");
    args.Update = Update<Entity>.Set(e => e.last_update, DateTime.Now);
    args.Fields = Fields.Include(new string[] { "counter", "_id" });
    var m = collection.FindAndModify(args);

    Entity ent = m.GetModifiedDocumentAs<Entity>();
    var query = Query<Entity>.EQ(e => e.Id, ent.Id);
    var update = Update<Entity>.Set(e => e.counter, ent.counter+1);
    collection.Update(query, update);
}