How does ServiceStack Redis function in retrieving

Not sure if it's the best title for the question... maybe someone could rename it for me?

My question is regarding performance of reading and combining data in c# ServiceStack wrapper for Redis and how the calls work internally.

I will explain two scenarios that will hopefully yield in a final result. One scenario has the list of category id's attached to the Transaction so that the Category can be stored independently.

Question: My end goal is to retrieve all transactions that have category 'food'.

I have tried to number other points where clarity would help my understanding. Consider there being 10,000 transactions and each transaction had on average 3 categories.

Note: There is a related question at ServiceStack.Net Redis: Storing Related Objects vs. Related Object Ids however doesn't explain the efficiency.

Example A

public class Transaction
{
    public List<string> CategoryIds;
}

Example B

public class Transaction
{
    public List<string> CategoryNames;
}

Code

var transactionClient = redisClient.GetTypedClient<Transaction>();

//1. is this inefficient returning all transactions?
//   is there any filtering available at this part?
var allTransactions = transactionClient.GetAll();

//2. In the case of Example A where the categories are stored as id's
//   how would I map the categories to a transaction?
//   maybe I have a List that has a container with the Transaction associated with a
//   list of Categories, however this seems inefficient as I would have to loop 
//   through all transactions make a call to get their Categories and then 
//   populate the container datatype.

//3. If we are taking Example B how can I efficiently just retrieve the transactions
//   where they have a category of food.

The efficiency is less network calls vs more data. Data in Redis just gets blobbed, most of the time a single API call maps 1:1 with a redis server operation. Which means you can think about the perf implications as simply downloading a json dataset blob from a remote server's memory and deserializing it on the client - which is effectively all that happens.

In some APIs such as GetAll() it requires 2 calls, 1 to fetch all the ids in the Entity set, and the other to fetch all the records with those ids. The source code of the Redis Client is quite approachable so I recommend having a look to see exactly what's happening.

Because you've only got 3 categories, it's not that much extra data you're saving by trying to filter on the server.

So your options are basically:

Download the entire entity dataset and filter on the client
Maintain a custom index mapping from Category > Ids
More Advanced: Use a server-side LUA operation to apply server side filtering (requires Redis 2.6)