Google datastore - index a date created field with

问题:

I am using Google Datastore and will need to query it to retrieve some entities. These entities will need to be sorted by newest to oldest. My first thought was to have a date_created property which contains a timestamp. I would then index this field and sort on this field. The problem with this approach is it will cause hotspots in the database (https://cloud.google.com/datastore/docs/best-practices).

Do not index properties with monotonically increasing values (such as a NOW() timestamp). Maintaining such an index could lead to hotspots that impact Cloud Datastore latency for applications with high read and write rates.

Obviously sorting data on dates is properly the most common sorting performed on a database. If I can't index timestamps, is there another way I can accomplish being able to sort my queires from newest to oldest without hotspots?

回答1:

As you note, indexing monotonically changed values doesn't scale and can lead to hotspots. Whether you are potentially impacted by this depends on your particular usage.

As a general rule, the hotspotting point of this pattern is 500 writes per second. If you know you're definitely going to stay under that you probably don't need to worry.

If you do need higher than 500 writes per second, but have a upper limit in mind, you could attempt a sharded approach. Basically, if you upper on writes per second is x, then n = ceiling(x/500), where n is the number of shards. When you write your timestamp, prepend random(1, n) at the start. This creates n random key ranges that each can perform up to 500 writes per second. When you query your data, you'll need to issue n queries and do some client side merging of the result streams.