该方法给集合添加一个标识，来修改集合的行为。 标识包含usePowerOf2Sizes和index。

命令格式为：

db.runCommand({"collMod":
     
      ,"
      
       ":
       
        })
       
      
     

 

检查标记设置：db.collection.stats()结果中的userFlags

 

1.通过collMod的标记修改TTL集合的过期时间：

#创建TTL集合

> db.log_events.createIndex({"createdAt": 1},{expireAfterSeconds: 360}) {        "createdCollectionAutomatically" : true,        "numIndexesBefore" : 1,        "numIndexesAfter" : 2,        "ok" : 1}> db.log_events.insert({	"createdAt": new Date(),	"logEvent": 2,    "logMessage": "Success!"	})WriteResult({ "nInserted" : 1 })> db.log_events.find(){ "_id" : ObjectId("56e4d6b51f83a0ff9e45be1c"), "createdAt" : ISODate("2016-03-13T02:55:49.002Z"), "logEvent" : 2, "logMessage" : "Success!" }

#查看TTL索引信息

> db.log_events.getIndexes()[        {                "v" : 1,                "key" : {                        "_id" : 1                },                "name" : "_id_",                "ns" : "test.log_events"        },        {                "v" : 1,                "key" : {                        "createdAt" : 1                },                "name" : "createdAt_1",                "ns" : "test.log_events",                "expireAfterSeconds" : 360        }]

#使用collMod修改TTL过期时间

#格式为{keyPattern: <TTL索引>, expireAfterSeconds: <修改后的过期时间> }

> db.runCommand({collMod: 'log_events', index: {keyPattern:{createAt:1}, expireAfterSeconds:800}}){        "ok" : 0,        "errmsg" : "cannot find index { createAt: 1.0 } for ns test.log_events",        "code" : 72}> db.runCommand({collMod: 'log_events', index: {keyPattern:{createdAt:1}, expireAfterSeconds:800}}){ "expireAfterSeconds_old" : 360, "expireAfterSeconds_new" : 800, "ok" : 1 }>