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https://issues.apache.org/jira/browse/FLINK-34129?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17811167#comment-17811167
]
xuyang commented on FLINK-34129:
--------------------------------
If the upstream CDC data is incomplete, such as receiving UB before UA, and
there is no I data before UB, taking SUM as an example, the global group
aggregation will first emit (+I, key, -1), then emit (-D, key, -1). This leads
to the final data being deleted.
This bug can be reproduced by adding the code in `TableSinkITCase` below.
{code:java}
@TestTemplate
def test(): Unit = {
val tableConfig = tEnv.getConfig
tableConfig.set(TABLE_EXEC_MINIBATCH_ENABLED, Boolean.box(true))
tableConfig.set(TABLE_EXEC_MINIBATCH_ALLOW_LATENCY, Duration.ofSeconds(1))
tableConfig.set(TABLE_EXEC_MINIBATCH_SIZE, Long.box(1L))
val userDataId = TestValuesTableFactory.registerData(
Seq(
changelogRow("-U", "k1", new JLong(1L)),
changelogRow("+U", "k1", new JLong(1L))
))
tEnv.executeSql(s"""
|CREATE TABLE TT (
| a STRING,
| b BIGINT
|) WITH (
| 'connector' = 'values',
| 'bounded' = 'false',
| 'changelog-mode' = 'I,UA,UB,D',
| 'data-id' = '$userDataId'
|)
|""".stripMargin)
val sql =
"""
|SELECT a, SUM(b)
|FROM TT GROUP BY a
""".stripMargin
tEnv.executeSql(sql).print
} {code}
The return values are:
{code:java}
+----+--------------------------------+----------------------+
| op | a | EXPR$1 |
+----+--------------------------------+----------------------+
| +I | k1 | -1 |
| -D | k1 | -1 |
+----+--------------------------------+----------------------+
2 rows in set {code}
> MiniBatchGlobalGroupAggFunction will make -D as +I then make +I as -U when
> state expired
> -----------------------------------------------------------------------------------------
>
> Key: FLINK-34129
> URL: https://issues.apache.org/jira/browse/FLINK-34129
> Project: Flink
> Issue Type: Bug
> Components: Table SQL / Runtime
> Affects Versions: 1.18.1
> Reporter: Hongshun Wang
> Priority: Major
> Fix For: 1.19.0
>
>
> 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.
> {code:java}
> if (stateAcc == null) {
> stateAcc = globalAgg.createAccumulators();
> firstRow = true;
> } {code}
> * then sum accumulator will retract sum value as -20
> * As the first row, MiniBatchGlobalGroupAggFunction will change -U as +I,
> then emit to downstream.
> {code:java}
> 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);
> } {code}
> * 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.
> {code:java}
> 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);
> } {code}
>
> So the sink will receiver +I and -D after a source update operation, the data
> will be delete.
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