I’ve been dabbling with CosmosDb and am now starting to get in the range of over 10k documents instead of just a few.
I’m struggling with how best to partition.
Some background
• I will have 10-50k documents in CosmosDb (maybe more in later phases)
• I have an index on top of those in Azure Search, for a small subset of these document’s properties)
• I will NOT be performing complex searches in CosmosDb
except:
• I will be fetching documents from cosmosDb by their Id (most likely coming from Azure Search results, when the user clicks one of the results)
o Initially only 1 document will be requested
o Possibly, in the future, I might ask for e.g. 10 documents at the same time, all by their Id.
I currently have 1 partition, which feels like a waste of a good system.
I could partition on e.g. the last digit of the document number, which would give a nice spread of documents across 10 partitions.
My concrete question:
If I spread data equally (almost randomly, to be honest) across 10 partitions, does that speed up fetching documents by Id (assuming many simultaneous calls to the system, each fetching 1 document by Id).
My reasoning: The last digit would determine the partition, so only 1 partition would be accessed to find the document, which is better than searching all partitions at the same time?
Spreading data across partitions does not make things faster on the read path in a partitioned data store. Where it helps is on the write path because you are spreading the load out horizontally across many computers simultaneously. And this only matters where the amount of throughput overloads what a single partition can achieve. For Cosmos DB this is 10,000 RU.
The key to fast reads is to indicate the partition key value in your read. The partition key is basically a router to where your data is stored. Once there it uses the index (or id in your case) to find the data.
There's some articles that provide some details on partitioning that are helpful.
Partitioning in Azure Cosmos DB
How to model and partition data on Azure Cosmos DB using a real-world example
Hope this helps.
Related
I have read that a single partition of DynamoDB has a size limit of 10GB. This means if all my data are smaller as 10GB then I have only one partition?
There is also a limit of 3000 RCUs or 1000 WCUs on a single partition. This means this is also the limit for a small database which has only one partition?
I use the billing mode PAY_PER_REQUEST. On the database there are short usage peaks of approximate 50MB data. And then there is nothing for hours. How can I design the database to get the best peak performance? Or is DynamoDB a bad option for this use case?
How to design a database to get best performance and picking the right database... these are deep questions.
DynamoDB works well for a wide variety of use cases. On the back end it uses partitions. You rarely have to think about partitions until you're at the high-end of scale. Are you?
Partition keys are used as a way to map data to partitions but it's not 1 to 1. If you don't follow best practice guidance and use one PK value, the database may still split the items across back-end partitions to spread the load. Just don't use a Local Secondary Index (LSI) or it prohibits this ability. The details of the mapping depend on your usage pattern.
One physical partition will be 10 GB or less, and has the 3,000 Read units and 1,000 Write units limit, which is why the database will spread load across partitions. If you use a lot of PK values you make it more straightforward for the database to do this.
If you're at a high enough scale to hit the performance limits, you'll have an AWS account manager you can ask to hook you up with a DynamoDB specialist.
A given partition key can't receive more than 3k RCUs/1k WCUs worth of requests at any given time and store more than 10GB in total if you're using an LSI (if not using an LSI, you can store more than 10GB assuming you're using a Sort Key). If your data definitely fits within those limits, there's no reason you can't use DDB with a single partition key value (and thus a single partition). It'd still be better to plan on a design that could scale.
The right design for you will depend on what your data model and access patterns look like. Given what you've described of some kind of periodic job, a timestamp could be used (although it has issues with hotspots you should be careful of). If you've got some kind of other unique id, like user_id or device_id, etc. that would be a better choice. There is some great documentation on that here.
We’re developing a personnel management system based on blazor and Cosmos DB serverless. There will be one customer per database and around 30 “docTypes”. The biggest categories by number and data volume are "users" and "employees". When we query we get all data of users and employee at once. So it can be several thousand. The other doctypes are much smaller an less frequently queried.
The volume of data per customer will not exceed 5 GByte. The most frequent queries are to 3 docTypes.
Would it make more sense to use customerId (so all data is in one partition) or docType as a partition key?
thanks
Based on the information you supplied it sound like docType is a good property to use as partition key, since it can be used to avoid cross partition queries. Especially since you state this will be often be used in your queries. With the max size you stated it will also be unlikely to cause you issues as a single partition can contain up to 20GB of data.
One thing to watch out for is Hot Partitioning. You state that your users partition might be a lot bigger than others. That can result into one partition doing all of the lifting while the others sit mostly idle which results and causing inefficiëncy of your total throughput.
On the other side it won't really matter for your use case. Since none of the databases will exceed that 5GB you'll always stay within a single partition, but it's always good though to think about it beforehand; As situations may change and you end up with a database that does split into partitions.
Lastly I would never use a single partition for all data. It has no benefits. If you have no properties that could serve as partition key then id is the better choice (so a logical partition per document). It won't hit storage limitations and evenly distributes throughput between partitions.
I would highly recommend you first take a look at this segment of the Data Modelling & Partitioning presentation by Thomas Weiss, Cosmos DB program manager. In my view it's one of the best resources to understand how to think about partitioning.
Do agree with David Makogon that you didn't provide enough data. For instance, we know there are 30 doc types per single database - given cosmosdb database uses containers, I actually expect each docType to have its own container - contrary to what you wrote:
Would it make more sense to use customerId (so all data is in one partition) or docType as a partition key?
Which suggests you want to use a single container for all your data. I wouldn't keep users and employees as documents in the same container. They are separate domains and deserve their own container.
See Azure docs page on Partition Strategy and subsequent paragraph about access patterns. The recommendation is to:
Choose a partition key that enables access patterns to be evenly spread across logical partitions.
In the access patterns section, the good practice mentioned is to separate data into hot, medium and cold data and place it into their own containers. One caveat is, that according to this page the max number of containers per database with shared throughput is 25.
If that is not possible, and all data has to end up in a single container, then docType seems to be the right partition key, because your queries will get data by docType if I understood correctly.
As 404 wrote, you want to avoid Hot Partitioning i.e. jamming most of documents in a container into a single or a few logical partitions. Therefore you want to choose a partition key based on most frequent operations.
My application need to support lookups for invoices by invoice id and by the customer. For that reason I created two collections in which I store the (exact) same invoice documents:
InvoicesById, with partition key /InvoiceId
InvoicesByCustomerId, with partition key /CustomerId
Apparently you should use partition keys when doing queries and since there are two queries I need two collections. I guess there may be more in the future.
Updates are primarily done to the InvoicesById collection, but then I need to replicate the change to InvoicesByCustomer (and others) as well.
Are there any best practice or sane approaches how to keep collections in sync?
I'm thinking change feeds and what not. I want avoid writing this sync code and risk inconsistencies due to missing transactions between collections (etc). Or maybe I'm missing something crucial here.
Change feed will do the trick though I would suggest to take a step back before brute-forcing the problem.
Please find detailed article describing split issue here: Azure Cosmos DB. Partitioning.
Based on the Microsoft recommendation for maintainable data growth you should select partition key with highest cardinality (in your case I assume it will be InvoiceId). For the main reason:
Spread request unit (RU) consumption and data storage evenly across all logical partitions. This ensures even RU consumption and storage distribution across your physical partitions.
You don't need creating separate container with CustomerId partition key as it won't give you desired, and most importantly, maintainable performance in future and might result in physical partition data skew when too many Invoices linked to the same customer.
To get optimal and scalable query performance you most probably need InvoiceId as partition key and indexing policy by CustomerId (and others in future).
There will be a slight RU overhead (definitely not multiplication of RUs but rather couple additional RUs per request) in consumption when data you're querying is distributed between number of physical partitions (PPs) but it will be neglectable comparing to issues occurring when data starts growing beyond 50-, 100-, 150GB.
Why CustomerId might not be the best partition key for the data sets which are expected to grow beyond 50GB?
Main reason is that Cosmos DB is designed to scale horizontally and provisioned throughput per PP is limited to the [total provisioned per container (or DB)] / [number of PP].
Once PP split occurs due to exceeding 50GB size your max throughput for existing PPs as well as two newly created PPs will be lower then it was before split.
So imagine following scenario (consider days as a measure of time between actions):
You've created container with provisioned 10k RUs and CustomerId partition key (which will generate one underlying PP1). Maximum throughput per PP is 10k/1 = 10k RUs
Gradually adding data to container you end-up with 3 big customers with C1[10GB], C2[20GB] and C3[10GB] of invoices
When another customer was onboarded to the system with C4[15GB] of data Cosmos DB will have to split PP1 data into two newly created PP2 (30GB) and PP3 (25GB). Maximum throughput per PP is 10k/2 = 5k RUs
Two more customers C5[10GB] C6[15GB] were added to the system and both ended-up in PP2 which lead to another split -> PP4 (20GB) and PP5 (35GB). Maximum throughput per PP is now 10k/3 = 3.333k RUs
IMPORTANT: As a result on [Day 2] C1 data was queried with up to 10k RUs
but on [Day 4] with only max to 3.333k RUs which directly impacts execution time of your query
This is a main thing to remember when designing partition keys in current version of Cosmos DB (12.03.21).
What you are doing is a good solution. Different queries requires different Partition Keys on different Cosmos DB Containers with same data.
How to sync the two Containers: use Triggers from the firs Container.
https://devblogs.microsoft.com/premier-developer/synchronizing-azure-cosmos-db-collections-for-blazing-fast-queries/
Cassandra has a Feature called Materialized Views for this exact problem, abstracting the sync problem. Maybe some day same Feature will be included on Cosmos DB.
According to docs, documents with different partitionKey may end up in same partition but documents with same partitionKey are guaranteed to end up in same partition.
Now, lets consider a case where you have partitionKey with cardinality=100 (for example 100 tenants).
Initially, all data is roughly equally distributed across partitions.
Lety say you end up with partitions of about 50GB size. I would assume in that case you might have a few partition keys contained within same partition. Then, all of the sudden your 2 tenants grow exponentially and they go to 200GB size.
Since partition have 250GB limit, now you're in problem.
Questions:
How is this being solved?
Is DocumentDB partitioning handling this moving to separate partitions?
Should we (and are we even able to) view data/storage consumption per partitionKey (not partition)?
If someone could shed a bit of light to these dilemas as i couldnt find answers to these specific questions in docs.
Currently, the logical partition for Single partition key cannot exceed 10GB. It means you have to ensure that at any given point of the time your logical partition does not exceed 10GB.
Source MSDN
A logical partition is a partition within a physical partition that stores all the data associated with a single partition key value. A logical partition has a 10 GB max.
On your question.
How is this being solved?
Choosing the appropriate partition key and ensure it is well balanced. If you anticipate that a tenant data might grow beyond 10GB, then having tenant id as partition key is not an option. You have to have something else as a partition key which can be scalable.
Is DocumentDB partitioning handling this moving to separate partitions?
Yes, CosmosDB will take care of Physical Partition handling.
Should we (and are we even able to) view data/storage consumption per partitionKey (not partition)?
Yes, In the Azure portal, go to Azure Cosmos DB account and click on Metrics in Monitoring section and then on right pane click on storage tab to see how your data is partitioned in different physical partition
The Microsoft advice for partition-key selection encourages the selection of a key that will lead to 100's or 1000's of partitions. The general theme is "more is better".
My question is, can a CosmosDb suffer from a partition key that leads to an excessive number of highly fragmented logical partitions?
I am considering using a partition-key that defines a team-workgroup id and which also equates to a customer tenant boundary. This partition-key maps very well onto data query and transaction boundary access patterns in my application. However, I am concerned that with just 100 stored docs per tenant and an estimated 50 kb of storage per tenant, by the time my CosmosDb collection reaches 10Gb the collection would have 200,000 partitions.
Please note: I already understand that a logical partition does not
map 1:1 to a physical CosmosDb partition and in my proposed case a
physical partition is likely to contain 1000+ logical partitions.
There is no practical limit to the number of logical partitions you are allowed to have. The system can scale to millions or billions of logical partitions. It's just a simple hash operation on your partition key to determine which physical partition holds the logical partition that your document lives in.