Fix the bug when aggregation stops before a group is finished #3177
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@@ -22,6 +22,7 @@ | |
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| import com.apple.foundationdb.annotation.API; | ||
| import com.apple.foundationdb.async.AsyncUtil; | ||
| import com.apple.foundationdb.record.ByteArrayContinuation; | ||
| import com.apple.foundationdb.record.RecordCursor; | ||
| import com.apple.foundationdb.record.RecordCursorContinuation; | ||
| import com.apple.foundationdb.record.RecordCursorResult; | ||
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@@ -57,77 +58,104 @@ public class AggregateCursor<M extends Message> implements RecordCursor<QueryRes | |
| // Previous non-empty record processed by this cursor | ||
| @Nullable | ||
| private RecordCursorResult<QueryResult> previousValidResult; | ||
| // last row in last group, is null if the current group is the first group | ||
| @Nullable | ||
| private RecordCursorResult<QueryResult> lastInLastGroup; | ||
| @Nullable | ||
| byte[] continuation; | ||
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| public AggregateCursor(@Nonnull RecordCursor<QueryResult> inner, | ||
| @Nonnull final StreamGrouping<M> streamGrouping, | ||
| boolean isCreateDefaultOnEmpty, | ||
| @Nullable byte[] continuation) { | ||
| this.inner = inner; | ||
| this.streamGrouping = streamGrouping; | ||
| this.isCreateDefaultOnEmpty = isCreateDefaultOnEmpty; | ||
| this.continuation = continuation; | ||
| } | ||
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| @Nonnull | ||
| @Override | ||
| public CompletableFuture<RecordCursorResult<QueryResult>> onNext() { | ||
| if (previousResult != null && !previousResult.hasNext()) { | ||
| // we are done | ||
| return CompletableFuture.completedFuture(RecordCursorResult.withoutNextValue(previousResult.getContinuation(), | ||
| previousResult.getNoNextReason())); | ||
| } | ||
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| return AsyncUtil.whileTrue(() -> inner.onNext().thenApply(innerResult -> { | ||
| previousResult = innerResult; | ||
| if (!innerResult.hasNext()) { | ||
| if (!isNoRecords() || (isCreateDefaultOnEmpty && streamGrouping.isResultOnEmpty())) { | ||
| // the method streamGrouping.finalizeGroup() computes previousCompleteResult and resets the accumulator | ||
| streamGrouping.finalizeGroup(); | ||
| } | ||
| return false; | ||
| } else { | ||
| final QueryResult queryResult = Objects.requireNonNull(innerResult.get()); | ||
| boolean groupBreak = streamGrouping.apply(queryResult); | ||
| if (groupBreak) { | ||
| lastInLastGroup = previousValidResult; | ||
| } else { | ||
| // previousValidResult is the last row before group break, it sets the continuation | ||
| previousValidResult = innerResult; | ||
| } | ||
| return (!groupBreak); | ||
| } | ||
| }), getExecutor()).thenApply(vignore -> { | ||
| // either innerResult.hasNext() = false; or groupBreak = true | ||
| if (Verify.verifyNotNull(previousResult).hasNext()) { | ||
| // in this case groupBreak = true, return aggregated result and continuation | ||
| RecordCursorContinuation continuation = Verify.verifyNotNull(previousValidResult).getContinuation(); | ||
| /* | ||
| * Update the previousValidResult to the next continuation even though it hasn't been returned. This is to return the correct continuation when there are single-element groups. | ||
| * Below is an example that shows how continuation(previousValidResult) moves: | ||
| * Initial: previousResult = null, previousValidResult = null | ||
| row0 groupKey0 groupBreak = False previousValidResult = row0 previousResult = row0 | ||
| row1 groupKey0 groupBreak = False previousValidResult = row1 previousResult = row1 | ||
| row2 groupKey1 groupBreak = True previousValidResult = row1 previousResult = row2 | ||
| * returns result (groupKey0, continuation = row1), and set previousValidResult = row2 | ||
| * | ||
| * Now there are 2 scenarios, 1) the current iteration continues; 2) the current iteration stops | ||
| * In scenario 1, the iteration continues, it gets to row3: | ||
| row3 groupKey2 groupBreak = True previousValidResult = row2 previousResult = row3 | ||
| * returns result (groupKey1, continuation = row2), and set previousValidResult = row3 | ||
| * | ||
| * In scenario 2, a new iteration starts from row2 (because the last returned continuation = row1), and set initial previousResult = null, previousValidResult = null: | ||
| row2 groupKey1 groupBreak = False previousValidResult = row2 previousResult = row2 | ||
| * (Note that because a new iteration starts, groupBreak = False for row2.) | ||
| row3 groupKey2 groupBreak = True previousValidResult = row2 previousResult = row3 | ||
| * returns result (groupKey1, continuation = row2), and set previousValidResult = row3 | ||
| * | ||
| * Both scenarios returns the correct result, and continuation are both set to row3 in the end, row2 is scanned twice if a new iteration starts. | ||
| */ | ||
| previousValidResult = previousResult; | ||
| return RecordCursorResult.withNextValue(QueryResult.ofComputed(streamGrouping.getCompletedGroupResult()), continuation); | ||
| } else { | ||
| if (Verify.verifyNotNull(previousResult).getNoNextReason() == NoNextReason.SOURCE_EXHAUSTED) { | ||
| if (previousValidResult == null) { | ||
| return RecordCursorResult.exhausted(); | ||
|
There was a problem hiding this comment. Does this need to check to insert the empty result if Perhaps it would be simpler if there were fewer moving parts here. If we wait until 4.2, we could drop support entirely for |
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| } else { | ||
| RecordCursorContinuation continuation = previousValidResult.getContinuation(); | ||
| previousValidResult = previousResult; | ||
| return RecordCursorResult.withNextValue(QueryResult.ofComputed(streamGrouping.getCompletedGroupResult()), continuation); | ||
| } | ||
| } else { | ||
| RecordCursorContinuation currentContinuation; | ||
| // in the current scan, if current group is the first group, set the continuation to the start of the current scan | ||
| // otherwise set the continuation to the last row in the last group | ||
| if (lastInLastGroup == null) { | ||
| currentContinuation = continuation == null ? RecordCursorStartContinuation.START : ByteArrayContinuation.fromNullable(continuation); | ||
| } else { | ||
| currentContinuation = lastInLastGroup.getContinuation(); | ||
| } | ||
| previousValidResult = lastInLastGroup; | ||
| return RecordCursorResult.withoutNextValue(currentContinuation, Verify.verifyNotNull(previousResult).getNoNextReason()); | ||
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There was a problem hiding this comment. Should this also set That is: RecordCursor<T> aggCursor = getAggregateCursor();
RecordCursorResult<T> withValueResult = aggCursor.getNext(); // has a value
RecordCursorResult<T> withoutValueResult1 = aggCursor.getNext(); // first result with out-of-bound limit; continuation borrowed from withValueResult
RecordCursorResult<T> withoutValueResult2 = aggCursor.getNext(); // second result with out-of-bound limit; continuation may be greater than withoutValueResult1In general, once a cursor returns a |
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| } | ||
| } | ||
| }); | ||
| } | ||
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| private boolean isNoRecords() { | ||
| return ((previousValidResult == null) && (!Verify.verifyNotNull(previousResult).hasNext())); | ||
| } | ||
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It looks like this still hasn't marked the
continuationfield as private. Is there a reason it needs package visibility?