How to efficiently query data from FDB?

Using FoundationDB
1

Few days back I posted on this forum asking about the way to structure data in FDB. I received very patient and informative replies from @markus.pilman

In those replies it was mentioned that a better way to structure data in FDB is to associate the primary key with the complete table data/record as the value, stored in an efficient format such as protobuf. For example, a student table {uuid, name, address} could be represented in FDB as (uuid, {name, address}) where name and address are stored as protobuf encoded value for the uuid key.

So, my question is, how do I efficiently query data that is encoded in the value? Say, I want to find all students whose name is ‘Bandu’; do I need to query the FDB server for each student record, decode the protobuf value, and then check for the name? What will be the performance implications of this approach? Am I thinking in the wrong direction again? What is a better way to query data in FDB?

2

FDB allows to query by a key or a key range, uuid in your case. So if you need to query by a part of value efficiently, you have create secondary key-value pairs: {name+uuid, }. Then you will be able to query by name using the range with the prefix name and to get a list of uuids of the students with given name, then, to query their data by uuid.

You can use the Record Layer on top of fdb, that does a part of this work automatically. There is a special part Using Layers in this community forum.

3

What are the performance implications of querying the DB server twice?

4

Of cause, the performance will be lower.

If it is not acceptable, you may duplicate data and insert two pairs:

  • {uuid, {name, address}}
  • {name+uuid, address}