Azure - Querying 200 million entities

问题:

I have a need to query a store of 200 million entities in Windows Azure. Ideally, I would like to use the Table Service, rather than SQL Azure, for this task.

The use case is this: a POST containing a new entity will be incoming from a web-facing API. We must query about 200 million entities to determine whether or not we may accept the new entity.

With the entity limit of 1,000: does this apply to this type of query, i.e. I have to query 1,000 at a time and perform my comparisons / business rules, or can I query all 200 million entities in one shot? I think I would hit a timeout in the latter case.

Ideas?

回答1:

Expanding on Shiraz's comment about Table storage: Tables are organized into partitions, and then your entities are indexed by a Row key. So, each row can be found extremely fast using the combination of partition key + row key. The trick is to choose the best possible partition key and row key for your particular application.

For your example above, where you're searching by telephone number, you can make TelephoneNumber the partition key. You could very easily find all rows related to that telephone number (though, not knowing your application, I don't know just how many rows you'd be expecting). To refine things further, you'd want to define a row key that you can index into, within the partition key. This would give you a very fast response to let you know whether a record exists.

Table storage (actually Azure Storage in general - tables, blobs, queues) have a well-known SLA. You can execute up to 500 transactions per second on a given partition. With the example above, the query for rows for a given telephone number would equate to one transaction (unless you exceed 1000 rows returned - to see all rows, you'd need additional fetches); adding a row key to narrow the search would, indeed, yield a single transaction). So would inserting a new row. You can also batch up multiple row inserts, within a single partition, and save them in a single transaction.

For a nice overview of Azure Table Storage, with some good labs, check out the Platform Training Kit.

For more info about transactions within tables, see this msdn blog post.

回答2:

The limit of 1000 is the number of rows returned from a query, not the number of rows queried.

Pulling all of the 200 million rows into the web server to check them will not work.

The trick is to store the rows with a key that can be used to check if the record should be accepted.