AggAPI.lua

This UDF will help you with arbitrary aggregations on the Aerospike database. You need to register this lua UDF on the server using your client's API, and then use aggregation API on your chosen Aerospike Client to call it with required parameters.

Limitations

Aerospike Server supports Lua 5.1, in which all numbers are floats with 51 bits significands (52 with sign bit). This means integers bigger than 2^51 will return invalid values.

How to setup?

You need to register the provided aggAPI.lua file as a UDF in your database.

Using Go to register the module:

Here an example in Go (note that for the sake of conciseness, the errors are not checked in this example):

luaFile, _ := ioutil.ReadFile("aggAPI.lua")
regTask, _ := client.RegisterUDF(nil, luaFile, "aggAPI.lua", aero.LUA)
// wait until UDF is created on the server.
_ <-regTask.OnComplete()

For more information: Go Client register UDF.

Using Java to register the module:

RegisterTask task = client.register(params.policy, "udf/aggAPI.lua", "aggAPI.lua", Language.LUA);
// Alternately register from resource.
task.waitTillComplete();

For more information: Java Client register UDF.

Using AQL to register the module:

aql> register module 'aggAPI.lua'

For more information: manging UDF using AQL.

How does it work?

The Lua streaming UDF will use the argument you pass to it in its calculations by evaling the arguments, and then using them in its logic to calculate and filter the records mostly on the server-side.

    "fields": {
        "name":            "name",
        "max(age)":        {"func": "max", "expr": "rec['age'] ~= nil and rec['age']"},
        "count(age)":      {"func": "count", "expr": "( rec['age'] ) ~= nil and 1"},
        "min(age)":        {"func": "min", "expr": "rec['age'] ~= nil and rec['age']"},
        "sum(age*salary)": {"func": "sum", "expr": " (rec['age']  or 0) * (rec['salary'] or 0)"},
    },
    "filter": "rec['age'] ~= nil and rec['age'] >5 ",
    "group_by_fields": {
      "name"
    }

A last pass will occur on client-side and the results will return in the following format:

{
  "8de6a795aaf29f2a7dad71c6631a1efc": {
    "count(age)":      3.000000,
    "max(age)":        45.000000,
    "count":           3.000000,
    "sum(age*salary)": 101400,
    "min(age)":        25.000000,
    "name":            "Eva",
  },
  "ed57af7ff6ed54ec8b6b5eec3e2b649a": {
    "count(age)":      1.000000,
    "max(age)":        26.000000,
    "count":           1.000000,
    "sum(age*salary)": 83200,
    "min(age)":        26.000000,
    "name":            "Riley",
  },
}

The key is a hash used to group the results for reduction. The value is a map of the returned fields. In the map, the key is the alias of the field.

Keep in mind that the values are limited to the size of Lua's value size, which is 51 bits of significant integer values.

What is the meaning of the values sent to the UDF?

There are 3 different input that need to be sent to the Lua UDF. Not all are required for every command. These values are:

• "fields": Choosing the fields to return - this is the equivalent of the select part of the query.

  • Fields which do not require any complex calculation: the map key is the alias, while the map value is the name of the existing bin in the database.
    Example:

    fields": {
      "age": "age",  
      "salary_usd" : "salary"  
    }

  • Fields which are calculated (apply an aggregate function on): the map key is the aliases, and the value is a map of the function and its calculation. Available functions are count, sum, min, max.

    Example:

    "fields": {
      "sum(salary * 2)": {"func": "sum", "expr": "rec['salary'] * 2"}, 
      "min(salary)":     {"func": "sum", "expr": "rec['salary']"},
      "max(salary * 5)": {"func": "sum", "expr": "(rec['salary'] or 0) * 5"}
    }

    • "sum(salary * 2)": {"func": "sum", "expr": "rec['salary'] * 2"} means a field with the name sum(salary * 2) should be calculated from the value of the bin salary multiplied by 2.
    • "min(salary)": {"func": "sum", "expr": "rec['salary']"}: use the value of the bin salary to calculate min(salary)
    • "max(salary * 5)": {"func": "sum", "expr": "(rec['salary'] or 0) * 5"}: use the value of the bin salary multiplied by 5 to calculate the max value. If the salary bin is null, 0 will be used as default value.

• "filter": Filter is a lua boolean statement to filter records - this is the equivalent of a where in a query.
  If the value of the statement is true, the record will be included in the results.

  Example:
  "filter": "rec['age'] ~= nil and rec['age'] > 25"

• "group_by_fields": List of field aliases to group the records by - this is the equivalent of group by in a query.
  Example:

  "group_by_fields": [
      "age", "salary_udf"
   ]

Example: Building a Query

How can I calculate a sum?

To calculate the equivalent of the following SQL:

select sum(salary) from employees

We would call the select_agg_records function with following argument:

{
  "fields":         {
    "sum(salary)": {"func": "sum" , "expr": "rec['salary'] or 0"},
  },
}

Which means use the value of the bin salary. If the salary bin is null or does not exist, 0 will be used as default value. We name this calculation sum(salary).

Adding a conditions

To add a filtering condition:

select sum(salary) from employees where age > 25

provide the following arguments:

{
  "fields":         {
    "sum(salary)": {"func": "sum" , "expr": "rec['salary'] or 0"},
  },
  "filter":    "rec['age'] ~= nil and rec['age'] > 25",
}

Which means check if the age bin exists, and if it does, check if the age is over 25.

Adding a Group BY

To create a group by aggregation, we would need to add the fields both to the fields part and to the group by.

select name, age, sum(salary) from employees where age > 25 group by name, age

provide the following arguments:

{
  "fields":         {
    "age":  "age",
    "name": "name",
    "sum(salary)": {"func": "sum" , "expr": "rec['salary'] or 0"},
  },
  "filter":    "rec['age'] ~= nil and rec['age'] > 25",
  "group_by_fields": [
    "age",
    "name",
  ],
}

Please note: the UDF logic does not validate if your provided group by arguments are valid for the logic of the equivalent SQL command.

Adding min and max functions

To add other fields to the query like:

select age, min(salary), max(salary), sum(salary) from employees where age > 25 group by age

provide the following arguments:

{
  "fields":         {
    "age": "age",
    "min(salary)": {"func": "min" , "expr": "rec['salary']"},
    "max(salary)": {"func": "max" , "expr": "rec['salary']"},
    "sum(salary)": {"func": "sum" , "expr": "rec['salary']"},
  },
  "filter":    "rec['age'] ~= nil and rec['age'] > 25",
  "group_by_fields": [
    "age",
  ],
}

Can I do more complex statements in the functions and filters?

YES! The execute the equivalent of the following SQL command:

select age, min(salary), max(salary), sum(salary * 2) from employees where age > 25 group by age

provide the following arguments:

{
  "fields":         {
    "age": "age",
    "sum(salary * 2)": {"func": "sum" , "expr": "rec['salary'] * 2"},
    "min(salary)":     {"func": "min" , "expr": "rec['salary']"},
    "max(salary)":     {"func": "max" , "expr": "rec['salary']"},
  },
  "filter":    "rec['age'] ~= nil and rec['age'] > 25",
  "group_by_fields": [
    "age",
  ],
}

How can I calculate average?

The UDF does not have an avg function so there is no equivalent for this SQL query:

select age, avg(salary) from employees group by age

Calculating the average needs to be done manually by the client - query sum and count and calculate the avg from them.

Using the UDF to get sum and count:

{
  "fields":         {
    "age": "age",
    "sum(salary)":     {"func": "sum" , "expr": "rec['salary']"},
    "count(*)":        {"func": "count" , "expr": "1"}
  },
  "group_by_fields": [
    "age",
  ],
}

How can I do DISTINCT queries?

In case you would want to return the following SQL statement:

select distinct age from employees

since you can rewrite the above query as:

select age from employees group by age

then the parameters sent to the UDF would be:

{
  "fields": {
    "age": "age",
  },
  "group_by_fields": [
    "age",
  ],
}

Code Examples

Example in Go:

stm := aero.NewStatement(nsName, setName)

functionArgsMap := map[string]interface{}{
  "fields": map[string]interface{}{
    "name":            "name",
    "max(age)":        map[string]string{"func": "max", "expr": "rec['age'] ~= nil and rec['age']"},
    "count(age)":      map[string]string{"func": "count", "expr": "( rec['age'] ) ~= nil and 1"},
    "min(age)":        map[string]string{"func": "min", "expr": "rec['age'] ~= nil and rec['age']"},
    "sum(age*salary)": map[string]string{"func": "sum", "expr": " (rec['age']  or 0) * (rec['salary'] or 0)"},
  },
  "filter": "rec['age'] ~= nil and rec['age'] >5 ",
  "group_by_fields": []string{
    "name",
  },
}

recordset, err := client.QueryAggregate(nil, stm, "aggAPI", "select_agg_records", aero.NewValue(functionArgsMap))
defer recordset.Close()

if err != nil {
  return err
}

for result := range recordset.Results() {
  if result.Err != nil {
    return result.Err
  }

  pp.Println(result.Record.Bins["SUCCESS"])
}

Example in Java:

String stringToParse = String.format("{\n" +
    "  \"fields\":         {\n" +
    "    \"test_id\": \"test_id\",\n" +
    "    \"state\": \"state\",\n" +
    "    \"count(state)\": {\"func\":\"count\", \"expr\": \"rec['state'] ~= nil and 1\"},\n" +
    "  },\n" +
    "  \"filter\":    \"rec['test_id'] ~= nil and rec['test_id'] == %s\",\n" +
    "  \"group_by_fields\": [\n" +
    "    \"test_id\",\n" +
    "    \"state\",\n" +
    "  ],\n" +
    "}", testId.toString());

JSONObject json = new JSONObject(stringToParse);
Map functionArgsMap  = toMap(json);

Statement stmt = new Statement();
stmt.setNamespace(namespace);
stmt.setSetName(set);
stmt.setBinNames(binName);

// Optional filter via Index
stmt.setFilter(Filter.equal(binName, testId));
stmt.setIndexName(indexName);

ResultSet rs = client.queryAggregate(null, stmt,"aggAPI","select_agg_records", Value.get(functionArgsMap));

try {
  if (rs.next()) {
    Object obj = rs.getObject();

    if (obj instanceof Map<?, ?>) {
      Map<String, Map> map = (Map<String, Map>) obj;

        map.values().forEach(res -> {
            console.info(res.toString());

            console.info("res: %s, %s => %s",
                    res.get("test_id"),
                    res.get("state"),
                    res.get("count(*)"));
      }
    }
  }
}

finally {
  rs.close();
}