Re: Unexpected hop start & end timestamps after stream SQL join

Posted by Juho Autio on
URL: http://deprecated-apache-flink-user-mailing-list-archive.369.s1.nabble.com/Unexpected-hop-start-end-timestamps-after-stream-SQL-join-tp18336p18594.html

Thanks for the hint! For some reason it isn't catching all distinct values (even though it's a much simpler way than what I initially tried and seems good in that sense). First of all, isn't this like a sliding window: "rowtime RANGE BETWEEN INTERVAL '1' HOUR PRECEDING AND CURRENT ROW"?

My use case needs a tumbling window. I tried adding PARTITION BY additionally with DATE_FORMAT(rowtime, '%Y%m%d%H') to achieve the same result as with a tumbling window; this resulted in slightly more distinct values, but was still missing some! Would there by some nice way to create a tumbling window right in the RANGE condition instead?

As a disclaimer I have to say we seem to be fine using a simple window _without_ any early triggering. But of course it would be nice to understand how early triggering could be enabled in a simple & scalable way.

Cheers,

Juho

On Mon, Feb 19, 2018 at 1:44 PM, Fabian Hueske <[hidden email]> wrote:

Hi Juho,

sorry for the late response. I found time to look into this issue.

I agree, that the start and end timestamps of the HOP window should be 1 hour apart from each other. I tried to reproduce the issue, but was not able to do so.

Can you maybe open a JIRA and provide a simple test case (collection data source, no Kafka) that reproduces the issue?

Regarding the task that you are trying to solve, have you looked into OVER windows?

The following query would count for each record, how often a record with the same ID combination was observed in the last hour based on its timestamp:

SELECT
  s_aid1,

  s_cid,

  COUNT(*) OVER (PARTITION BY s_aid1, s_cid ORDER BY rowtime RANGE BETWEEN INTERVAL '1' HOUR PRECEDING AND CURRENT ROW) AS occurrence,

  rowtime

FROM events

WHERE s_aid1 IS NOT NULL

If occurrence is 1, the current record is the only record within the last 1 hour with the combination of aid and cid .

The query does not batch the stream by 10 seconds, but rather produces the results in real-time. If the batching is not required, you should be good by adding a filter on occurrence = 1.
Otherwise, you could add the filter and wrap it by 10 secs tumbling window.

Hope this helps,

Fabian

2018-02-14 15:30 GMT+01:00 Juho Autio <[hidden email]>:

I'm joining a tumbling & hopping window in Flink 1.5-SNAPSHOT. The result is unexpected. Am I doing something wrong? Maybe this is just not a supported join type at all? Any way here goes:

I first register these two tables:

1. new_ids: a tumbling window of seen ids within the last 10 seconds:

SELECT

  s_aid1,

  s_cid,

  TS_MIN(rowtime) AS first_seen,

  CAST(DATE_FORMAT(TUMBLE_START(rowtime, INTERVAL '10' SECOND), '%Y%m%d/%H/%i/%S') AS VARCHAR) AS processdate,

  TUMBLE_START(rowtime, INTERVAL '10' SECOND) AS tumble_start,

  TUMBLE_END(rowtime, INTERVAL '10' SECOND) AS tumble_end

FROM events

WHERE s_aid1 IS NOT NULL

GROUP BY

  s_aid1,

  s_cid,

  TUMBLE(rowtime, INTERVAL '10' SECOND)

2. seen_ids: a sliding window of seen ids 1 hour backwards, 10 second hop:

SELECT

  s_aid1,

  s_cid,

  TS_MIN(rowtime) AS first_seen,

  CAST(HOP_START(rowtime, INTERVAL '10' SECOND, INTERVAL '1' HOUR) AS DATE) AS processdate,

  HOP_START(rowtime, INTERVAL '10' SECOND, INTERVAL '1' HOUR) AS HOP_start,

  HOP_END(rowtime, INTERVAL '10' SECOND, INTERVAL '1' HOUR) AS HOP_end

FROM events

WHERE s_aid1 IS NOT NULL

GROUP BY

  s_aid1,

  s_cid,

  HOP(rowtime, INTERVAL '10' SECOND, INTERVAL '1' HOUR)

If I write the results of the "seen_ids" table, the difference between HOP_start and HOP_end is always 1 hour, as expected.

Then I register another query that joins the 2 tables:

unique_ids (mostly including fields for debugging - what I need is the unique, new combinations of s_cid x s_aid1):

SELECT

   new_ids.s_cid,

   new_ids.s_aid1,

   new_ids.processdate AS processdate,

   seen_ids.processdate AS seen_ids_processdate,

   new_ids.first_seen AS new_ids_first_seen,

   seen_ids.first_seen AS seen_ids_first_seen,

   tumble_start,

   HOP_start,

   tumble_end,

   HOP_end

FROM new_ids, seen_ids

WHERE new_ids.s_cid = seen_ids.s_cid

  AND new_ids.s_aid1 = seen_ids.s_aid1

  AND (new_ids.first_seen <= seen_ids.first_seen OR seen_ids.first_seen IS NULL)

I print the results of this table, and surprisingly the HOP_start & HOP_end are only separated by 10 seconds. Is this a bug?

{

  "s_cid": "appsimulator_236e5fb7",

"s_aid1": "L1GENe52d723b-b563-492f-942d-3dc1a31d7e26",

"seen_ids_processdate": "2018-02-14",

"seen_ids_first_seen": "2018-02-14 11:37:59.0",

"new_ids_first_seen":  "2018-02-14 11:34:33.0",

"tumble_start": "2018-02-14 11:34:30.0",

"tumble_end": "2018-02-14 11:34:40.0",

"HOP_start": "2018-02-14 11:37:50.0",

"HOP_end": "2018-02-14 11:38:00.0"

}

What I'm trying to do is exclude the id from the current "new_ids" window if it was already seen before (within the 1 hour scope of "seen_ids"), but that doesn't work either. This example result row also shows that "seen_ids.first_seen" is bigger than it should be.

Even if I can find a fix to this to get what I need, this strategy seems overly complicated. If anyone can suggest a better way, I'd be glad to hear. If this was a batch job, it could be defined simply as:

SELECT DISTINCT s_cid, s_aid1, DATE_FORMAT(rowtime, '%Y%m%d/%H')

+ when streaming this query, the new distinct values should be written out every 10 seconds (ONLY the new ones - within that wrapping 1 hour window). So far I haven't been able to figure out how to do that in a simple way with Flink.

*) TS_MIN is a custom function, but it's just a mapping of Flink's MinAggFunction:

import java.sql.Timestamp

import com.rovio.ds.flink.common.udaf.ImplicitOrdering.ordered

import org.apache.flink.api.common.typeinfo.SqlTimeTypeInfo

import org.apache.flink.table.functions.aggfunctions.MaxAggFunction

import org.apache.flink.table.functions.aggfunctions.MinAggFunction

object TimestampAggFunctions {

  trait TimestampAggFunction {

    def getInitValue = null

    def getValueTypeInfo = SqlTimeTypeInfo.TIMESTAMP

  }

  class TimestampMinAggFunction extends MinAggFunction[Timestamp] with TimestampAggFunction

  class TimestampMaxAggFunction extends MaxAggFunction[Timestamp] with TimestampAggFunction

}

// Registered with:

tableEnv.registerFunction("TS_MIN", new TimestampMinAggFunction());