MiniBatchGlobalGroupAggFunction will make -D as +I then make +I as -U when state expired

Take sum for example:
When state is expired, then an update operation from source happens. MiniBatchGlobalGroupAggFunction take -U[1, 20] and +U[1, 20] as input, but will emit +I[1, -20] and -D[1, -20]. The sink will detele the data from external database.

Let's see why this will happens:

• when state is expired and -U[1, 20] arrive, MiniBatchGlobalGroupAggFunction will create a new sum accumulator and set firstRow as true.

if (stateAcc == null) { 
    stateAcc = globalAgg.createAccumulators(); 
    firstRow = true; 
}   

• then sum accumulator will retract sum value as -20
• As the first row, MiniBatchGlobalGroupAggFunction will change -U as +I, then emit to downstream.

if (!recordCounter.recordCountIsZero(acc)) {
   // if this was not the first row and we have to emit retractions
    if (!firstRow) {
       // ignore
    } else {
    // update acc to state
    accState.update(acc);
 
   // this is the first, output new result
   // prepare INSERT message for new row
   resultRow.replace(currentKey, newAggValue).setRowKind(RowKind.INSERT);
   out.collect(resultRow);
}  

• when next +U[1, 20] arrives, sum accumulator will retract sum value as 0, so RetractionRecordCounter#recordCountIsZero will return true. Because firstRow = false now, will change the +U as -D, then emit to downtream.

if (!recordCounter.recordCountIsZero(acc)) {
    // ignode
}else{
   // we retracted the last record for this key
   // if this is not first row sent out a DELETE message
   if (!firstRow) {
   // prepare DELETE message for previous row
   resultRow.replace(currentKey, prevAggValue).setRowKind(RowKind.DELETE);
   out.collect(resultRow);
} 

 
So the sink will receiver +I and -D after a source update operation, the data will be delete.