以 UTC 存储时间总是一个好主意，还是以本地时间存储更好? [英] Is it always a good idea to store time in UTC or is this the case where storing in local time is better?

问题描述

一般来说，最好的做法是在 UTC 中存储时间，如 这里和这里.

Generally, it is the best practice to store time in UTC and as mentioned in here and here.

假设有一个重复发生的事件，假设结束时间总是在同一本地时间假设 17:00，无论该时区是否开启或关闭夏令时.并且还要求在特定时区的 DST 打开或关闭时不要手动更改时间.还要求任何其他系统通过 API(即 GetEndTimeByEvent)询问结束时间时始终以 UTC 格式发送结束时间.

Suppose there is a re-occurring event let's say end time which is always at the same local time let's say 17:00 regardless of whether there is Daylight saving is on or off for that time zone. And also there is a requirement not to change the time manually when DST turns ON or OFF for particular time zone. It is also a requirement that whenever end time is asked by any other systems through API (i.e. GetEndTimeByEvent) it always sends the end time in UTC format.

方法一:如果决定以 UTC 存储，则可以将其存储在数据库表中，如下所示.

Approach 1: If it is decided to store in UTC it can be stored in the database table as below.

Event      UTCEndTime
=====================
ABC         07:00:00
MNO         06:00:00
PQR         04:00:00

对于第一个事件 ABC，UTC 的结束时间是上午 07:00，如果转换为 2012 年 7 月 1 日从 UTC 显示为本地时间，它将导致本地时间 17:00，如果转换为 10 月 10 日-2012(时区 DST 开启的日期)将导致下午 6 点，这不是正确的结束时间.

For the first event ABC, end time in UTC is 07:00 am which if converted to display from UTC to local time on 1-July-2012 it will result into 17:00 local time and if converted on 10-Oct-2012 (the date when DST is ON for the time zone) then will result into 6 pm which is not correct end time.

我能想到的一种可能方法是将夏令时时间存储在附加列中，并在时区开启夏令时时使用该时间.

One possible way I could think is to store DST time in the additional column and using that time when the timezone has DST ON.

方法二:但是，如果它存储为本地时间，例如对于事件 ABC，它在任何日期将始终为 17:00，因为没有从 UTC 转换为本地时间.

Approach 2: However, if it is stored as Local time as below for example for event ABC it will be always 17:00 on any date as there is no conversion to from UTC to local time.

Event      LocalEndTime
=======================
ABC         17:00:00
MNO         16:00:00
PQR         14:00:00

应用层将本地时间转换为UTC时间，通过(API GetEndTimeByEvent)发送给其他系统.

And an application layer converts local time to UTC time to send to other systems through (API GetEndTimeByEvent).

在这种情况下，以 UTC 格式存储时间仍然是个好主意吗?如果是，那么如何获得恒定的当地时间?

相关问题:是否有充分的理由不使用 UTC 存储时间?

推荐答案

我认为为了回答这个问题，我们应该考虑使用 UTC 存储时间戳的好处.

I think that in order to answer that question, we should think about the benefits of using UTC to store timestamps.

我个人认为这样做的主要好处是时间总是(大部分)保证一致.换句话说，无论何时更改时区或应用 DST，您都不会及时返回或返回.这在文件系统、日志等中特别有用.但它在您的应用程序中有必要吗?

I personally think that the main benefit to that is that the time is always (mostly) guaranteed to be consistent. In other words, whenever the timezone is changed, or DST applied, you don't get back or forth in time. This is especially useful in filesystems, logs and so on. But is it necessary in your application?

想两件事.首先，关于夏令时时钟移位的时间.您的活动是否有可能发生在凌晨 2 点到凌晨 3 点之间(在时钟轮班结束的那一天)?那应该怎么办?

Think of two things. Firstly, about the time of DST clock shift. Is it likely that your events are going to occur between 2 AM and 3 AM (on the day the clock shift is done)? What should happen then?

其次，应用程序是否会受到实际时区变化的影响?换句话说，你打算带着它从伦敦飞到华沙，并适当地改变你的电脑时区吗?在这种情况下应该怎么办?

Secondly, will the application be subject to actual timezone changes? In other words, are you going to fly with it from London to Warsaw, and change your computer timezone appropriately? What should happen in that case?

如果您对这两个问题的回答否，那么您最好使用当地时间.它将使您的应用程序更简单.但如果你至少回答了一次是，那么我认为你应该多考虑一下.

If you answered no to both of those questions, then you're better with the local time. It will make your application simpler. But if you answered yes at least once, then I think you should give it more thinking.

这就是数据库的全部内容.另一件事是应用程序内部使用的时间格式，这应该取决于您将如何处理该时间.

And that was all about the database. The other thing is the time format used internally by the application, and that should depend on what actually you will be doing with that time.

您提到它通过 API 公开时间.应用程序会在每个请求上查询数据库吗?如果您在内部将时间存储为 UTC，您将需要这样做或以其他方式确保在 DST/时区更改时缓存时间将被调整/修剪.

You mentioned it exposing the time via an API. Will the application query the database on every request? If you store the time internally as UTC, you will either need to do that or otherwise ensure that on DST/timezone change the cached times will be adjusted/pruned.

它会对时间本身做些什么吗?就像打印事件将在 8 小时内发生 或在大约那个时间暂停自身?如果是，那么UTC可能会更好.当然，您需要考虑所有上述问题.

Will it do anything with the time itself? Like printing the event will occur in 8 hours or suspending itself for circa that time? If yes, then UTC will probably be better. Of course, you need to think of all the forementioned issues.

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