Millisecond precise timestamp field in DynamoDB stream

Question

I have a DynamoDB table where I enabled DynamoDB stream. I also have a trigger which invokes Lambda function when item is changed.

Is there any millisecond-precise timestamp field in DynamoDB stream I can rely on?

I'd like to rely on it in downstream services which are sensitive to the order of messages.

score 0 · Answer 1 · answered May 06 '21 at 14:18

0

As you probably already know, the ApproximateCreationDateTime on the stream is, as its name suggests, not all that accurate. If you need order I would use the SequenceNumber, which is in order. If you must have a timestamp you'll have to include it in your data, but be aware that the time you create the timestamp in your data is not the same as when the data is added to the table. In many cases that's fine, but if you have more than one process writing you could have process A created a timestamp that is before process B, but the data from B could be written to the table before the data from A.

answered May 06 '21 at 14:18

Jason Wadsworth

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Sequence number is unique per partition-key within its shard. Every partition has its own shard. Partitions can be split because of 10GB limit. This indicates to me that there is some chance of sequence number conflict in downstream services. Is my understanding correct? – Patrik Mihalčin May 06 '21 at 16:35
Yes. There isn’t anything that is going to guarantee order across partition keys. You can look at the partition key and sequence number to get ordering within a partition. – Jason Wadsworth May 06 '21 at 17:11
Will sequence number be always unique for the same partition key? – Patrik Mihalčin May 06 '21 at 17:40
The sequence number is unique and always increasing (though not always by 1). – Jason Wadsworth May 06 '21 at 18:32
Are sequence numbers unique only for 24 hours? – Patrik Mihalčin May 07 '21 at 09:09

Millisecond precise timestamp field in DynamoDB stream

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