Should I copy a session for each operation in mgo?

Question

I want a upsertlist of entries, so I have two options: one just uses one session, another instance of the session for each entry. So, in my opinion, the first method may slow down than the second, but will the first cause too many sessions?

1. use one session

func (this *CvStoreServiceImpl) SetCvJobItemMeasureList(accessToken *base_datatype.ServiceAccessToken, versionPolicy string, jobItemList []*cv_common_type.CvJobItemMeasure) (err error) {
    session := this.session.Clone()
    defer session.Close()

    for _, jobItem := range jobItemList {
        objKey := &orm.ItemIdKey{
            VersionName: versionPolicy, //XXX
            ItemId:      jobItem.ItemId,
        }
        obj := orm.ConvertToCvJobItemMeasureObj(versionPolicy, jobItem)
        _, err2 := this.jobMeasureCollection.With(session).Upsert(objKey, obj)
        if nil != err2 {
            err = &common_error.NamedError{err2.Error()}
            this.logger.Println(err2.Error())
        }
    }
    return
}

2. copy session for each record

func (this *CvStoreServiceImpl) SetCvJobItemMeasure(accessToken *base_datatype.ServiceAccessToken, versionPolicy string, jobItem *cv_common_type.CvJobItemMeasure) (err error) {
    session := this.session.Clone()
    defer session.Close()

    objKey := &orm.ItemIdKey{
        VersionName: versionPolicy, //XXX
        ItemId:      jobItem.ItemId,
    }
    obj := orm.ConvertToCvJobItemMeasureObj(versionPolicy, jobItem)
    _, err2 := this.jobMeasureCollection.With(session).Upsert(objKey, obj)
    if nil != err2 {
        err = &common_error.NamedError{err2.Error()}
        return
    }
    return
}

then call this method in forloop:

for _, item := range cvMeasure.GetJobList() {
    err = this.SetCvJobItemMeasure(accessToken, versionPolicy, item)
    if nil != err {
        return
    }
}

Answer 1

, mgo.Session.Copy() mgo.Session.Clone(). go.Session.Clone() , . , , . , . .

: , , . , , .

, , - (er) . :

package main

import (
    "fmt"
    mgo "gopkg.in/mgo.v2"
    bson "gopkg.in/mgo.v2/bson"
    "net/http"
)

var (
    Database *mgo.Database
)


// The listEntries lists all posts
func listPosts(w http.ResponseWriter, r *http.Request) {

    // We have a rather long running unit of work
    // (reading and listing all posts)
    // So it is worth copying the session   
    collection := Database.C("posts").With( Database.Session.Copy() )

    post  := bson.D{}
    posts := collection.Find(bson.M{}).Iter()

    for posts.Next(&post) {
        // Process posts and send it to w
    }

}

func main() {

    session, _ := mgo.Dial("mongodb://localhost:27017")

    Database := session.DB("myDb")

    // Count is a rather fast operation
    // No need to copy the session here
    count, _ := Database.C( "posts" ).Count()

    fmt.Printf("Currently %d posts in the database", count )

    http.HandleFunc("/posts", listPosts)
    http.ListenAndServe(":8080", nil)
}

Answer 2

, , mgo . 4096 mongo, .

func newSession(consistency Mode, cluster *mongoCluster, timeout time.Duration) (session *Session) {
    cluster.Acquire()
    session = &Session{
        cluster_:    cluster,
        syncTimeout: timeout,
        sockTimeout: timeout,
        poolLimit:   4096,
    }
    debugf("New session %p on cluster %p", session, cluster)
    session.SetMode(consistency, true)
    session.SetSafe(&Safe{})
    session.queryConfig.prefetch = defaultPrefetch
    return session
}