客户端之间的Firestore同步时间

Question

I have this document structure in firestore collection

{ message: 'hello world', time: 1538398128 }

time value is set by client when it posts message with this function

moment().unix()

The problem is that my clients have different time and if I sort documents by time it is inconsistent, like this example

{ message: 'aaa', time: 1538398317 } // client 1 post at 14.00:00
{ message: 'bbb', time: 1538398257 } // client 2 post at 14:00:10

and on client I see "bbb" before "aaa". How can I fix this problem? I know that exists firebase.firestore.FieldValue.serverTimestamp(), but it gives me the value only after I posted the document, i can't use this on client. Thanks

Answer 1

Well you will need to pick one timezone and use it as standard for a consistent data storage, otherwise every client will use the local one. You might want to use moment-timezone an extension for momentjs where you can specify the timezone you want to use : https://momentjs.com/timezone/

Answer 2

It is not possible to perfectly sync different client devices (phones/browsers) with time, as you have no mechanism to force their clocks to be in sync.

To ensure a consistent ordering, you will need to use firebase.firestore.FieldValue.serverTimestamp() , which once committed will be returned to the client. While you are waiting for it, you can use the client time as a fallback mechanism. Even better, you can reach out to some time server to validate that the local clock hasn't drifted too far from being usable.