GraphQL counter

Problem

You want to increment a counter via a GraphQL query.

Fauna provides consistent results that are globally replicated. High-volume counter updates to a single document (as shown in this solution) create contention that can slow down your queries.

We recommend alternatives such as:

  • batch your counter updates (multiple updates per query)

  • avoid counter updates faster than once or twice per second

Solution

There are several steps:

  1. Update your GraphQL schema to include:

    graphqlCopied!
    type Counter {
  counter: Int!
}

type Query {
  nextCounter: Counter! @resolver(name: "increment_counter")
}

    This involves editing the GraphQL schema definition, wherever you have stored it, and then uploading the new schema in the Fauna Dashboard.

  2. Create a UDF to perform the counter increment:

    Copied!
    ({
  name: "increment_counter",
  body: (
    (
      [],
      (
        {
          counterRef: (("Counter"), "1"),
          counter: (("counterRef")),
          counterValue: (["data", "counter"], ("counter"))
        },
        (
          ("counterRef"),
          {
            data: {
              counter: (("counterValue"), 1)
            }
          }
        )
      )
    )
  )
})
    {
  ref: ("increment_counter"),
  ts: 1626466930320000,
  name: 'increment_counter',
  body: (([], ({"counterRef": (("Counter"), "1"), "counter": (("counterRef")), "counterValue": (["data", "counter"], ("counter"))}, (("counterRef"), {"data": {"counter": (("counterValue"), 1)}}))))
}
    Query metrics:

    •    bytesIn:  401

    •   bytesOut:  501

    • computeOps:    1

    •    readOps:    0

    •   writeOps:    1

    •  readBytes:   30

    • writeBytes:  593

    •  queryTime: 22ms

    •    retries:    0

  3. Create the required Counter document:

    Copied!
    (
  (("Counter"), "1"),
  { data: { counter: 0 } }
)
    {
  ref: (("Counter"), "1"),
  ts: 1626466931300000,
  data: { counter: 0 }
}
    Query metrics:

    •    bytesIn:  106

    •   bytesOut:  165

    • computeOps:    1

    •    readOps:    0

    •   writeOps:    1

    •  readBytes:   14

    • writeBytes:  194

    •  queryTime: 42ms

    •    retries:    0

    Here, we have set the initial counter value to 0.

  4. Run a GraphQL query to increment the counter:

    graphqlCopied!
    {
  nextCounter {
    counter
  }
}

    You should see the result:

    {
  "data": {
    "nextCounter": {
      "counter": 1
    }
  }
}

  5. You can also increment the counter in FQL queries:

    Copied!
    ("increment_counter")
    {
  ref: (("Counter"), "1"),
  ts: 1626466932180000,
  data: { counter: 1 }
}
    Query metrics:

    •    bytesIn:   43

    •   bytesOut:  165

    • computeOps:    1

    •    readOps:    1

    •   writeOps:    1

    •  readBytes:   58

    • writeBytes:   85

    •  queryTime: 29ms

    •    retries:    0

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