Sort key of the local secondary index can be different. Amazon DynamoDB is a fast and flexible nonrelational database service for any scale. The last example of filter expressions is my favorite use — you can use filter expressions to provide better validation around TTL expiry. ... For the sort key, provide the timestamp value of the individual event. We’ll look at the following two strategies in turn: The most common method of filtering is done via the partition key. At this point, they may see the FilterExpression property that’s available in the Query and Scan API actions in DynamoDB. DynamoDB will periodically review your items and delete items whose TTL attribute is before the current time. There are two major drawbacks in using this map-style layout: The first is a hard limt and something that we can’t change without a significant change to the architecture. Let’s see how this might be helpful. You have to be able to quickly traverse time when doing any useful operation on IoT data (in essence, IoT data is just a bunch of events over time). We also saw a few ways that filter expressions can be helpful in your application. The filter expression states that the Sales property must be larger than 1,000,000 and the SK value must start with SONG#. This makes the Scan + filter expression combo even less viable, particularly for OLTP-like use cases. Many of these requests will return empty results as all non-matching items have been filtered out. Since DynamoDB wasn’t designed for time-series data, you have to check your expected data against the core capabilities, and in our case orchestrate some non-trivial gymnastics. You have to be able to quickly traverse time when doing any useful operation on IoT data (in essence, IoT data is just a bunch of events over time). The term “range attribute” derives from the way DynamoDB stores items with the same partition key physically close together, in sorted order by the sort key value. At Fineo we selected DynamoDB as our near-line data storage (able to answer queries about the recent history with a few million rows very quickly). Each item in a DynamoDB table requires that you create a primary key for the table, as described in the DynamoDB documentation. The hash isn’t a complete UUID though - we want to be able to support idempotent writes in cases of failures in our ingest pipeline. We’ll cover: This post contains some concepts from my Data Modeling with DynamoDB talk at AWS re:Invent 2019. In this article, we saw why DynamoDB filter expressions may not help the way you think. You could use the range key to store different content about the account, for example, you might have a sort key settings for storing account configuration, then a set of timestamps for actions. When you query a local secondary index, you can choose either eventual consistency or strong consistency. Your table might look as follows: In your table, albums and songs are stored within a collection with a partition key of ALBUM##. Copied from the link: DynamoDB collates and compares strings using the bytes of the underlying UTF-8 string encoding. This is assuming you have formatted the Timestamp correctly. For example, suppose you had an api key ‘n111’ and a table ‘a_table’, with two writes to the timestamp ‘1’, the row in the table would look like: Where 1234 and abc11 are the generated ‘unique enough’ IDs for the two events. Ask Question Asked 4 years, 11 months ago. I also have the ExpiresAt attribute, which is an epoch timestamp. There are three songs that sold more than 1,000,000 copies, so we added a SongPlatinumSalesCount for them. In the example portion of our music table, there are two different collections: The first collection is for Paul McCartney’s Flaming Pie, and the second collection is for Katy Perry’s Teenage Dream. The reason is that sorting numeric values is straight forward but then you need to parse that value to a user readable one. Each field in the incoming event gets converted into a map of id to value. Another valid approach would be to assume only one event per timestamp, and then rewrite the data if there is multiple events, but that leads to two issues: In the end, we decided to pursue a map-first approach. You might think you could use the Scan operation with a filter expression to make the following call: The example above is for Node.js, but similar principles apply for any language. The requested partition key must be an exact match, as it directs DynamoDB to the exact node where our Query should be performed. Once you’ve properly normalized your data, you can use SQL to answer any question you want. Primary keys, secondary indexes, and DynamoDB streams are all new, powerful concepts for people to learn. DynamoDB automatically handles splitting up into multiple requests to load all items. Timestamp (string) Query vs Scan. With this flexible query language, relational data modeling is more concerned about structuring your data correctly. Secondary indexes are a way to have DynamoDB replicate the data in your table into a new structure using a different primary key schema. I have one SQLite table per DynamoDB table (global secondary indexes are just indexes on the table), one SQLite row per DynamoDB item, the keys (the HASH for partitioning and the RANGE for sorting within the partition) for which I used a string are stored as TEXT in SQLite but containing their ASCII hexadecimal codes (hashKey and rangeKey). In the next section, we’ll take a look why. A single record label will have a huge number of songs, many of which will not be platinum. The naive, and commonly recommend, implementation of DynamoDB/Cassandra for IoT data is to make the timestamp part of the key component (but not the leading component, avoiding hot-spotting). The table is the exact same as the one above other than the addition of the attributes outlined in red. 2015-12-21T17:42:34Z. We don’t want all songs, we want songs for a single album. ), multiple data formats on read, increasing the complexity. But filter expressions in DynamoDB don’t work the way that many people expect. Use KSUID to have sortable unique ID as replacment of UUID in #DynamoDB #singletabledesign Amazon allows you to search your order history by month. So what should you use to properly filter your table? Each write that comes in is given a unique hash based on the data and timestamp. As such, you will use your primary keys and secondary indexes to give you the filtering capabilities your application needs. Then we explored how filter expressions actually work to see why they aren’t as helpful as you’d expect. DynamoDB enables customers to offload the administrative burdens of operating and scaling distributed databases to AWS so that they don’t have to worry about hardware provisioning, setup and configuration, throughput capacity planning, replication, software patching, or cluster scaling. You can use the string data type to represent a date or a timestamp. Thanks to Jeremy Daly for his assistance in reviewing this post. We then saw how to model your data to get the filtering you want using the partition key or sparse secondary indexes. You're on the list. This makes it easy to support additional access patterns. DynamoDB collates and compares strings using the bytes ... is greater than “z” (0x7A). It would be nice if the database automatically handled ‘aging off’ data older than a certain time, but the canonical mechanism for DynamoDB is generally to create tables that apply to a certain time range and then delete them when the table is no longer necessary. This can feel wrong to people accustomed to the power and expressiveness of SQL. The FilterExpression promises to filter out results from your Query or Scan that don’t match the given expression. For example, with smart cars, you can have a car offline for months at a time and then suddenly get a connection and upload a bunch of historical data. Spotify … In the last video, we created a table with a single primary key attribute called the partition key. Imagine we want to execute this a Query operation to find the album info and all songs for the Paul McCartney’s Flaming Pie album. Managing aging off data is generaly done by maintaining tables for a specific chunk of time and deleting them when they are too old. You can then issue queries using the between operator and two timestamps, >, or <. Partition Key and Sort Key in Amazon DynamoDB. DynamoDB will handle all the work to sync data from your main table to your secondary index. DynamoDB push-down operators (filter, scan ranges, etc.) There are limits that apply to data types. This allows to find all the tables for which data was written a while ago (and thus, likely to be old), and delete them when we are ready. This section describes the Amazon DynamoDB naming rules and the various data types that DynamoDB supports. I’ll set my TTL on this attribute so that DynamoDB will remove these items when they’re expired. On the whole DynamoDB is really nice to work with and I think Database as a Service (DaaS) is the right way for 99% of companies to manage their data; just give me an interface and a couple of knobs, don’t bother me with the details. In the operation above, we’re importing the AWS SDK and creating an instance of the DynamoDB Document Client, which is a client in the AWS SDK for Node.js that makes it easier for working with DynamoDB. Step 1: Create a DynamoDB Table with a Stream Enabled In this step, you create a DynamoDB table (BarkTable) to store all of the barks from Woofer users. For many, it’s a struggle to unlearn the concepts of a relational database and learn the unique structure of a DynamoDB single table design. The TTL is still helpful is cleaning up our table by removing old items, but we get the validation we need around proper expiry. DynamoDB Query Language in Node JS; Solution. This filters out all other items in our table and gets us right to what we want. First we saw why filter expressions trick a lot of relational converts to DynamoDB. Either write approach can be encoded into a state machine with very little complexity, but you must chose one or the other. In case you used any of those methods and you are still getting this warning, you most likely misspelled the timezone identifier. Instead, we can add the month/year data as a suffix to the event time range. DynamoDB supports many different data ... the maximum length of the second attribute value (the sort key) is 1024 bytes. With DynamoDB, you can create secondary indexes. In our music example, perhaps we want to find all the songs from a given record label that went platinum. If that fails, we could then attempt to do an addition to the column maps and id list. This essentially gives me the following pattern in SQL: We’ve now seen why filter expressions don’t work as you think they would and what you should use instead. ... You can use the number data type to represent a date or a timestamp. Better validation around time-to-live (TTL) expiry. DynamoDB query/sort based on timestamp. In addition to information about the album and song, such as name, artist, and release year, each album and song item also includes a Sales attribute which indicates the number of sales the given item has made. DynamoDB also lets you create tables that use two attributes as the unique identifier. AWS Data Hero providing training and consulting with expertise in DynamoDB, serverless applications, and cloud-native technology. In this table, my partition key is SessionId. Consider subscribing to the RSS feed. One way to do this is by using ISO 8601 strings, as shown in these examples: 2016-02-15 . Then we need to go and create the maps/list for the row with the new value. The timestamp part allows sorting. I prefer to do the filtering in my application where it’s more easily testable and readable, but it’s up to you. The most common way is to narrow down a large collection based on a boolean or enum value. Its kind of a weird, but unfortunately, not uncommon in many industries. Because we are using DynamoDB as our row store, we can only store one ‘event’ per row and we have a schema like: This leads us to the problem of how to disambigate events at the same timestamp per tenant, even if they have completely separate fields. Further, it doesn’t include any Song items with fewer than 1 million copies sold, as our application didn’t include the PlatinumSalesCount property on it. For example, "a " (0x61) is greater than "A However, filter expressions don’t work as you think they would. You might expect a single Scan request to return all the platinum songs, since it is under the 1MB limit. However, this can be a problem for users that have better than millisecond resolution or have multiple events per timestamp. Feel free to watch the talk if you prefer video over text. Imagine your music table was 1GB in size, but the songs that were platinum were only 100KB in size. This is how DynamoDB scales as these chunks can be spread around different machines. Secondary indexes can either be global, meaning that the index spans the whole table across hash keys, or local meaning that the index would exist within each hash key partition, thus requiring the hash key to also be specified when making the query. Then we added on a description of the more easy to read month and year the data was written. ... and the sort key the timestamp. Because the deletion process is out of an any critical path, and indeed happens asynchronously, we don’t have to be concerned with finding the table as quickly as possible.