On this put up I discover how you can help analytical queries with out encountering prohibitive scan prices, by leveraging secondary indexes in DynamoDB. I additionally consider the professionals and cons of this strategy in distinction to extracting knowledge to a different system like Athena, Spark or Elastic.
Rockset just lately added help for DynamoDB – which principally means you may run quick SQL on DynamoDB tables with none ETL. As I spoke to our customers, I got here throughout alternative ways during which international secondary indexes (GSI) are used for analytical queries.
DynamoDB shops knowledge beneath the hood by partitioning it over numerous nodes based mostly on a user-specified partition key subject current in every merchandise. This user-specified partition key may be optionally mixed with a form key to symbolize a main key. The first key acts as an index, making question operations on it cheap. A question operation can do equality comparability (=) on the partition key and comparative operations (>, <, =, BETWEEN) on the type key if specified. Performing operations that aren’t lined by the above scheme requires using a scan operation, which is usually executed by scanning over your entire DynamoDB desk in parallel. These scans may be gradual and costly by way of Learn Capability Models (RCUs) as a result of they require a full learn of your entire desk. Scans additionally are inclined to decelerate when the desk dimension grows as there may be extra knowledge to scan to provide outcomes.
If we need to help analytical queries with out encountering prohibitive scan prices, we are able to leverage secondary indexes in DynamoDB. Secondary indexes additionally consist of making partition keys and non-obligatory type keys over fields that we need to question over in a lot the identical approach as the first key. Secondary indexes are sometimes used to enhance utility efficiency by indexing fields that are queried fairly often. Question operations on secondary indexes may also be used to energy particular options by way of analytic queries which have clearly outlined necessities—like computing a leaderboard in a sport. One clear benefit of this strategy of performing analytical queries is that there isn’t any want for another system.
Nevertheless, it’s infeasible to make use of this strategy for a wider vary of analytical queries due to the restricted sorts of queries it helps. The total gamut of analytics requires filtering on a number of fields, grouping, ordering, becoming a member of knowledge between knowledge units, and many others., which can’t be achieved merely by way of secondary indexes. Secondary indexes that may be created are additionally restricted in quantity and require some planning to make sure that they scale properly with the info. A badly chosen partition key can worsen efficiency and enhance prices considerably. Knowledge in DynamoDB can have a nested construction together with arrays and objects, however indexes can solely be constructed on sure primitive sorts. This may drive denormalizing of the info to flatten nested objects and arrays so as to construct secondary indexes, which may probably explode the variety of writes carried out and related prices. Aside from value and suppleness, there are additionally safety and efficiency issues in the case of supporting analytic use instances on an operational knowledge retailer in a manufacturing surroundings.
Benefits
- No further setup outdoors DynamoDB
- Quick and scalable serving for primary analytical queries over listed fields
Disadvantages
- Costly when queries require scans over DynamoDB
- Very restricted help for analytical queries over indexes; no SQL queries, grouping, or joins
- Can not arrange indexes on nested fields with out denormalizing knowledge and exploding out writes
- Safety and efficiency implications of operating analytical queries on an operational database
This strategy could also be appropriate if we have now an utility that requires a selected function that’s easy sufficient to be realized utilizing a question over an index. The elevated storage and I/O value and the restricted question means make it unsuitable for the broader vary of analytical queries in any other case. Subsequently, for a majority of analytic use instances, it’s value efficient to export the info from DynamoDB into a distinct system that enables us to question with larger constancy.
If you’re contemplating extracting knowledge to a different system, there are a number of totally different choices for real-time analytics:
- DynamoDB + Glue + S3 + Athena
- DynamoDB + Hive/Spark
- DynamoDB + AWS Lambda + Elasticsearch
- DynamoDB + Rockset
I evaluate every of those by way of ease of setup, upkeep, question functionality, latency in my different weblog put up Analytics on DynamoDB: Evaluating Athena, Spark and Elastic, the place I additionally consider which use instances every of them are greatest fitted to.
Different DynamoDB sources:
