Wrong order when ordering by StringLast agg with GroupBy V2

[jon-wei]

Affected Version

0.13.0+

Description

A user on the mailing list reported the following issue: https://groups.google.com/d/msg/druid-user/x0xuqSFM794/C8tn3J4eDAAJ

The following data, index task, and queries can be used to reproduce the described issue:

data

{"time":"2015-09-12T00:46:58.771Z", "personId":"1111", "name":"ZZZZZ", "age": 30}
{"time":"2015-09-12T01:46:58.771Z", "personId":"1111", "name":"BBBBB", "age": 31}
{"time":"2015-09-12T02:46:58.771Z", "personId":"2222", "name":"YYYYY", "age": 20}
{"time":"2015-09-12T03:46:58.771Z", "personId":"2222", "name":"AAAAA", "age": 21}

task

{
  "type" : "index",
  "spec" : {
    "dataSchema" : {
      "dataSource" : "stringlaster",
      "parser" : {
        "type" : "string",
        "parseSpec" : {
          "format" : "json",
          "dimensionsSpec" : {
            "dimensions" : [
              "time",
              "personId",
              "name"
            ]
          },
          "timestampSpec" : {
            "format" : "auto",
            "column" : "time"
          }
        }
      },
      "metricsSpec" : [
        { "type" : "longSum", "name" : "age", "fieldName" : "age" }
      ],
      "granularitySpec" : {
        "type" : "uniform",
        "segmentGranularity" : "MONTH",
        "queryGranularity" : "none",
        "intervals" : ["2015-09-01/2015-10-01"],
        "rollup" : false
      }
    },
    "ioConfig" : {
      "type" : "index",
      "firehose" : {
        "type" : "local",
        "baseDir" : "quickstart/",
        "filter" : "stringlast_data.json"
      },
      "appendToExisting" : false
    },
    "tuningConfig" : {
      "type" : "index",
      "targetPartitionSize" : null,
      "maxRowsInMemory" : 25000,
      "forceGuaranteedRollup" : true,
      "numShards": 2
    }
  }
}

query, ordering by string last (wrong results):

{
  "queryType": "groupBy",
  "dataSource": { "type": "table", "name": "stringlaster" },
  "intervals": { "type": "intervals", "intervals": [ "2015-09-01/2015-10-01" ] },
  "granularity": { "type": "all" },
  "dimensions": [ "personId" ],
  "aggregations": [
    { "type": "stringLast", "name": "name", "fieldName": "name" },
    { "type": "longLast",   "name": "age", "fieldName": "age" }
  ],
  "limitSpec": {
    "type": "default", "limit": 1000,
    "columns" : [{ "dimension":"name","direction":"ascending","dimensionOrder":"alphanumeric"}]
  },
  "context": {}
}

wrong results for the above query:

[
  {
    "version": "v1",
    "timestamp": "2015-09-01T00:00:00.000Z",
    "event": {
      "name": "BBBBB",
      "personId": "1111",
      "age": 31
    }
  },
  {
    "version": "v1",
    "timestamp": "2015-09-01T00:00:00.000Z",
    "event": {
      "name": "AAAAA",
      "personId": "2222",
      "age": 21
    }
  }
]

query ordering by long last (correct results)

{
  "queryType": "groupBy",
  "dataSource": { "type": "table", "name": "stringlaster" },
  "intervals": { "type": "intervals", "intervals": [ "2015-09-01/2015-10-01" ] },
  "granularity": { "type": "all" },
  "dimensions": [ "personId" ],
  "aggregations": [
    { "type": "stringLast", "name": "name", "fieldName": "name" },
    { "type": "longLast",   "name": "age", "fieldName": "age" }
  ],
  "limitSpec": {
    "type": "default", "limit": 1000,
    "columns" : [{ "dimension":"age","direction":"ascending","dimensionOrder":"alphanumeric"}]
  },
  "context": {}
}

right results for above query:

[
  {
    "version": "v1",
    "timestamp": "2015-09-01T00:00:00.000Z",
    "event": {
      "name": "AAAAA",
      "personId": "2222",
      "age": 21
    }
  },
  {
    "version": "v1",
    "timestamp": "2015-09-01T00:00:00.000Z",
    "event": {
      "name": "BBBBB",
      "personId": "1111",
      "age": 31
    }
  }
]