mongodb

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":<collection>,"<flag>":<value>})

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 }
>