Background
The single desk design for DynamoDB simplifies the structure required for storing information in DynamoDB. As a substitute of getting a number of tables for every report kind you possibly can mix the several types of information right into a single desk. This works as a result of DynamoDB is ready to retailer very huge tables with various schema. DynamoDB additionally helps nested objects. This permits customers to mix PK because the partition key, SK as the kind key with the mixture of the 2 changing into a composite main key. Frequent columns can be utilized throughout report varieties like a outcomes column or information column that shops nested JSON. Or the totally different report varieties can have completely totally different columns. DynamoDB helps each fashions, and even a mixture of shared columns and disparate columns. Oftentimes customers following the only desk mannequin will use the PK as a main key inside an SK which works as a namespace. An instance of this:
Discover that the PK is similar for each data, however the SK is totally different. You possibly can think about a two desk mannequin like the next:
and
Whereas neither of those information fashions is definitely a superb instance of correct information modeling, the instance nonetheless represents the thought. The only desk mannequin makes use of PK as a main Key throughout the namespace of an SK.
How one can use the only desk mannequin in Rockset
Rockset has 2 methods of making integrations with DynamoDB. The primary is to use RCUs to scan the DynamoDB desk, and as soon as the preliminary scan is full Rockset tails DynamoDB streams. The opposite technique makes use of DynamoDB export to S3 to first export the DynamoDB desk to S3, carry out a bulk ingestion from S3 after which, after export, Rockset will begin tailing the DynamoDB streams. The primary technique is used for when tables are very small, < 5GB, and the second is far more performant and works for bigger DynamoDB tables. Both technique is suitable for the only desk technique.
Reminder: Rollups can’t be used on DDB.
As soon as the mixing is about up you’ve got a couple of choices to contemplate when configuring the Rockset collections.
Methodology 1: Assortment and Views
The primary and easiest is to ingest the entire desk right into a single assortment and implement views on prime of Rockset. So within the above instance you’ll have a SQL transformation that appears like:
-- new_collection
choose i.* from _input i
And you’ll construct two views on prime of the gathering.
-- consumer view
Choose c.* from new_collection c the place c.SK = 'Person';
and
--class view
choose c.* from new_collection c the place c.SK='Class';
That is the best strategy and requires the least quantity of data in regards to the tables, desk schema, sizes, entry patterns, and so on. Sometimes for smaller tables, we begin right here. Reminder: views are syntactic sugar and won’t materialize information, so that they should be processed like they’re a part of the question for each execution of the question.
Methodology 2: Clustered Assortment and Views
This technique is similar to the primary technique, besides that we’ll implement clustering when making the gathering. With out this, when a question that makes use of Rockset’s column index is run, all the assortment should be scanned as a result of there isn’t any precise separation of knowledge within the column index. Clustering could have no affect on the inverted index.
The SQL transformation will appear to be:
-- clustered_collection
choose i.* from _input i cluster by i.SK
The caveat right here is that clustering does devour extra sources for ingestion, so CPU utilization shall be increased for clustered collections vs non-clustered collections. The benefit is queries might be a lot quicker.
The views will look the identical as earlier than:
-- consumer view
Choose c.* from new_collection c the place c.SK = 'Person';
and
--class view
choose c.* from new_collection c the place c.SK='Class';
Methodology 3: Separate Collections
One other technique to contemplate when constructing collections in Rockset from a DynamoDB single desk mannequin is to create a number of collections. This technique requires extra setup upfront than the earlier two strategies however provides appreciable efficiency advantages. Right here we’ll use the the place clause of our SQL transformation to separate the SKs from DynamoDB into separate collections. This permits us to run queries with out implementing clustering, or implement clustering inside a person SK.
-- Person assortment
Choose i.* from _input i the place i.SK='Person';
and
-- Class assortment
Choose i.* from _input i the place i.SK='Class';
This technique doesn’t require views as a result of the info is materialized into particular person collections. That is actually useful when splitting out very giant tables the place queries will use mixes of Rockset’s inverted index and column index. The limitation right here is that we’re going to should do the export from DynamoDB for nonetheless many collections you need to create.
Methodology 4: Mixture of Separate Collections and Clustering
The final technique to debate is the mixture of the earlier strategies. Right here you’ll get away giant SKs into separate collections and use clustering and a mixed desk with views for the smaller SKs.
Take this dataset:
You possibly can construct two collections right here:
-- user_collection
choose i.* from _input i the place i.SK='Person';
and
-- combined_collection
choose i.* from _input i the place i.SK != 'Person' Cluster By SK;
After which 2 views on prime of combined_collection:
-- class_view
choose * from combined_collection the place SK='Class';
and
-- transportation_view
choose * from combined_collection the place SK='Transportation';
This offers you the advantages of separating out the big collections from the small collections, whereas maintaining your assortment dimension smaller, permitting different smaller SKs to be added to the DynamoDB desk with out having to recreate and re-ingest the collections. It additionally permits essentially the most flexibility for question efficiency. This selection does include essentially the most operational overhead to setup, monitor, and keep.
Conclusion
Single desk design is a well-liked information modeling approach in DynamoDB. Having supported quite a few DynamoDB customers by the event and productionization of their real-time analytics functions, we have detailed a number of strategies for organizing your DynamoDB single desk mannequin in Rockset, so you possibly can choose the design that works finest to your particular use case.
