wrong result in Apache flink full outer join - apache-flink

Question

I have 2 data streams which were created from 2 tables like:
Table orderRes1 = ste.sqlQuery(
"SELECT orderId, userId, SUM(bidPrice) as q FROM " + tble +
" Group by orderId, userId");
Table orderRes2 = ste.sqlQuery(
"SELECT orderId, userId, SUM(askPrice) as q FROM " + tble +
" Group by orderId, userId");
DataStream<Tuple2<Boolean, Row>> ds1 = ste.toRetractStream(orderRes1 , Row.class).
filter(order-> order.f0);
DataStream<Tuple2<Boolean, Row>> ds2 = ste.toRetractStream(orderRes2 , Row.class).
filter(order-> order.f0);
I wonder to perform a full outer join on these 2 streams, and I used both orderRes1.fullOuterJoin(orderRes2 ,$(exp))
and a sql query containing a full outer join, as below:
Table bidOrdr = ste.fromDataStream(bidTuple, $("orderId"),
$("userId"), $("price"));
Table askOrdr = ste.fromDataStream(askTuple, $("orderId"),
$("userId"), $("price"));
Table result = ste.sqlQuery(
"SELECT COALESCE(bidTbl.orderId,askTbl.orderId) , " +
" COALESCE(bidTbl.userId,askTbl.orderId)," +
" COALESCE(bidTbl.bidTotalPrice,0) as bidTotalPrice, " +
" COALESCE(askTbl.askTotalPrice,0) as askTotalPrice, " +
" FROM " +
" (SELECT orderId, userId," +
" SUM(price) AS bidTotalPrice " +
" FROM " + bidOrdr +
" Group by orderId, userId) bidTbl full outer JOIN " +
" (SELECT orderId, userId," +
" SUM(price) AS askTotalPrice" +
" FROM " + askOrdr +
" Group by orderId, userId) askTbl " +
" ON (bidTbl.orderId = askTbl.orderId" +
" AND bidTbl.userId= askTbl.userId) ") ;
DataStream<Tuple2<Boolean, Row>> = ste.toRetractStream(result, Row.class).filter(order -> order.f0);
However, the result in some cases in not correct: imagine user A sells with a price to B 3 times, after that user B sells to A 2 times, the second time the result is:
7> (true,123,a,300.0,0.0)
7> (true,123,a,300.0,200.0)
10> (true,123,b,0.0,300.0)
10> (true,123,b,200.0,300.0)
the second and forth lines are the expected result of stream, but it will generate the 1st and 3rd lines too.
worth mentioning that coGroup is the other solution, yet I do not want to use windowing in this scenario, and a non-windowing solution is just accessible in bounded streams (DataSet).
Hint: orderId and userId will repeat in both streams, and I want to produce 2 rows in each action, containing:
orderId, userId1, bidTotalPrice, askTotalPrice AND
orderId, userId2, bidTotalPrice, askTotalPrice

Answer 1

Something like this is to be expected with streaming queries (or in other words, with queries executed on dynamic tables). Unlike a traditional database, where the input relations to a query are kept static during query execution, the inputs to a streaming query are being continuously updated -- and so the result must also be continuously updated.
If I understand the setup here, the "incorrect" results on lines 1 and 3 are correct up until the relevant rows from orderRes2 are processed. If those rows never arrive, then lines 1 and 3 will remain correct.
What you should expect is an eventually correct result, including retractions as necessary. You can reduce the number of intermediate results by turning on mini-batch aggregation.
This mailing list thread gives more insight. If I've misunderstood your situation, please provide a reproducible example that illustrates the problem.