xiangfu0 commented on code in PR #19264:
URL: https://github.com/apache/pinot/pull/19264#discussion_r4127618593
##########
pinot-core/src/main/java/org/apache/pinot/core/util/GroupByUtils.java:
##########
@@ -87,6 +102,280 @@ public static GroupByResultsBlock
buildGroupingSetsResultsBlock(QueryContext que
return resultsBlock;
}
+ /// Derives the individual grouping sets from a merged BASE-grouping
[IndexedTable] (union columns aggregated
+ /// once, like a plain GROUP BY), for a GROUP BY GROUPING SETS / ROLLUP /
CUBE query using base aggregation.
+ /// Each base group is projected into every grouping set: its rolled-up
(non-participating) columns are set to
+ /// `null`, the `$groupingId` discriminator is inserted after the union
columns, and the base group's
+ /// aggregation intermediates are merged into the derived group. This moves
the per-set fan-out from O(rows) to
+ /// O(base groups) and runs it here -- after the row-collapsing base merge
-- across the combine's threads,
+ /// rather than expanding every scanned row.
+ ///
+ /// The grouping sets are partitioned round-robin across up to `numTasks`
worker tasks; each task derives its
+ /// owned sets over all base entries into a task-local plain HashMap. Task
key spaces are disjoint (every
+ /// derived key carries its set ordinal), so the heavy merge work runs
contention-free -- no concurrent table,
+ /// no bin locks, no shared size counters -- and the task maps are then
unioned single-threaded into the result
+ /// table with plain stores (never merges). Profiling showed the previous
shared-concurrent-table derive spent
+ /// most of its time in ConcurrentHashMap machinery rather than in the
projection itself.
+ ///
+ /// Clone discipline: a base group's intermediate flows into every grouping
set (and is read concurrently by
+ /// other tasks), while [AggregationFunction#merge] mutates/returns its
arguments. Each derived group's stored
+ /// accumulator is therefore a clone (see [#cloneIntermediate]), and OBJECT
intermediates are re-cloned per
+ /// merge so a merge can never mutate the shared base accumulator another
task is still reading. Scalar
+ /// intermediates are immutable and clone-free.
+ public static IndexedTable
deriveGroupingSetsFromMergedBaseTable(IndexedTable baseTable, QueryContext
queryContext,
+ int numTasks, ExecutorService executorService) {
+ AggregationFunction[] aggregationFunctions =
queryContext.getAggregationFunctions();
+ assert aggregationFunctions != null;
+ int numAggregationFunctions = aggregationFunctions.length;
+ List<int[]> groupingSets = queryContext.getGroupingSets();
+ int numSets = groupingSets.size();
+ int numUnionColumns = queryContext.getGroupByExpressions().size();
+ // Per grouping set: membership mask over the union columns (true =
participates, false = rolled up to NULL).
+ boolean[][] setContains = new boolean[numSets][numUnionColumns];
+ for (int s = 0; s < numSets; s++) {
+ for (int columnIndex : groupingSets.get(s)) {
+ setContains[s][columnIndex] = true;
+ }
+ }
+
+ // Grouping-set output schema: the base schema with the synthetic
$groupingId INT column inserted right after
+ // the union group-by columns (mirroring GroupByOperator's grouping-set
schema layout).
+ DataSchema groupingSetsSchema =
insertGroupingIdColumn(baseTable.getDataSchema(), numUnionColumns);
+ // The derive must not drop groups: it is a bounded transformation of the
already-bounded base groups (whose
+ // count is capped at numGroupsLimit per segment), so the derived count is
at most numGroupsLimit * numSets --
+ // a finite amount. Capping the derived table at numGroupsLimit would drop
derived groups NON-DETERMINISTICALLY
+ // under the parallel upsert (whichever threads fill the quota first win),
which can starve an entire
+ // low-magnitude grouping set such as the grand total. Use an unbounded
result size here and defer the real
+ // ORDER BY + LIMIT to the broker (per-set trim below still bounds it when
explicitly configured).
+ int derivedUpperBound = (int) Math.min((long) baseTable.size() * numSets,
Integer.MAX_VALUE);
+ int initialCapacity = getIndexedTableInitialCapacity(derivedUpperBound,
derivedUpperBound,
+ queryContext.getMinInitialIndexedTableCapacity());
+
+ List<Map.Entry<Key, Record>> baseEntries = new
ArrayList<>(baseTable.getRecordEntries());
+ // A full-union set (one that contains every union column, i.e. the
identity grouping) maps base groups to
+ // derived groups 1:1: keys are unique so no merge ever runs on its
records, and its stored intermediates can
+ // safely be the base objects themselves (all other readers of a base
intermediate treat it as read-only).
+ boolean[] isFullUnionSet = new boolean[numSets];
+ for (int s = 0; s < numSets; s++) {
+ boolean fullUnion = true;
+ for (int col = 0; col < numUnionColumns; col++) {
+ fullUnion &= setContains[s][col];
+ }
+ isFullUnionSet[s] = fullUnion;
+ }
+ int numTaskSlots = Math.max(1, Math.min(numTasks, numSets));
+ List<Map<Key, Record>> taskMaps;
+ if (numTaskSlots == 1) {
+ taskMaps = List.of(deriveSets(baseEntries, setContains, isFullUnionSet,
0, 1, numUnionColumns,
+ numAggregationFunctions, aggregationFunctions));
+ } else {
+ List<Future<Map<Key, Record>>> futures = new ArrayList<>(numTaskSlots);
+ for (int t = 0; t < numTaskSlots; t++) {
+ int taskIndex = t;
+ futures.add(executorService.submit(() -> deriveSets(baseEntries,
setContains, isFullUnionSet, taskIndex,
+ numTaskSlots, numUnionColumns, numAggregationFunctions,
aggregationFunctions)));
+ }
+ taskMaps = new ArrayList<>(numTaskSlots);
+ try {
+ // Bound each wait by the query deadline (when one is set) so a stuck
task cannot hold the combine past
+ // the timeout.
+ long endTimeMs = queryContext.getEndTimeMs();
+ for (Future<Map<Key, Record>> future : futures) {
+ if (endTimeMs > 0) {
+ taskMaps.add(future.get(Math.max(endTimeMs -
System.currentTimeMillis(), 0), TimeUnit.MILLISECONDS));
+ } else {
+ taskMaps.add(future.get());
+ }
+ }
+ } catch (InterruptedException e) {
+ cancelAll(futures);
+ Thread.currentThread().interrupt();
+ throw new RuntimeException("Interrupted while deriving grouping sets",
e);
+ } catch (TimeoutException e) {
+ cancelAll(futures);
+ throw new RuntimeException("Timed out while deriving grouping sets",
e);
+ } catch (ExecutionException e) {
+ cancelAll(futures);
+ throw new RuntimeException("Caught exception while deriving grouping
sets", e.getCause());
+ }
+ }
+
+ // Union the disjoint task maps into the result table. Since task key
spaces are disjoint, the union never
+ // merges records. In the common case, adopt the largest task map as the
table's backing map and putAll the
+ // rest into it, so the largest map's keys are never re-hashed. The
deterministic accurate-group-by mode
+ // needs a sorted (skip-list) backing map for deterministic iteration
order, so it keeps the upsert-based
+ // union into the table produced by getTrimDisabledIndexedTable
(single-threaded, numThreads = 1).
+ IndexedTable derivedTable;
+ if (useDeterministicIndexedTable(queryContext)) {
+ derivedTable = getTrimDisabledIndexedTable(groupingSetsSchema, false,
queryContext, Integer.MAX_VALUE,
+ initialCapacity, 1, executorService);
+ for (Map<Key, Record> taskMap : taskMaps) {
+ for (Map.Entry<Key, Record> entry : taskMap.entrySet()) {
+ derivedTable.upsert(entry.getKey(), entry.getValue());
+ }
+ }
+ } else {
+ Map<Key, Record> mergedMap = taskMaps.get(0);
+ for (Map<Key, Record> taskMap : taskMaps) {
+ if (taskMap.size() > mergedMap.size()) {
+ mergedMap = taskMap;
+ }
+ }
+ for (Map<Key, Record> taskMap : taskMaps) {
+ if (taskMap != mergedMap) {
+ mergedMap.putAll(taskMap);
+ }
+ }
+ derivedTable = new SimpleIndexedTable(groupingSetsSchema, false,
queryContext, Integer.MAX_VALUE,
+ Integer.MAX_VALUE, Integer.MAX_VALUE, mergedMap, executorService);
+ }
+
+ /// Optional server-side per-set trim: when configured (and there is an
ORDER BY), keep at most K groups
+ /// within each grouping set (bucketed by $groupingId), bounding this
server's derived output for
+ /// high-cardinality unions. Bucketing per set means a global top-K cannot
starve a low-magnitude set. This
+ /// is an approximate top-K (deferred exact ORDER BY + LIMIT still runs at
the broker); unset -> keep all.
+ int serverTrimSize = queryContext.getGroupingSetServerTrimSize();
+ if (serverTrimSize > 0 && derivedTable.size() > (long) serverTrimSize *
numSets) {
+ derivedTable.finish(false);
+ TableResizer tableResizer = new TableResizer(groupingSetsSchema,
queryContext);
+ List<IntermediateRecord> kept =
tableResizer.trimTableByGroupingSet(derivedTable, serverTrimSize,
+ numUnionColumns);
+
ServerMetrics.get().addMeteredGlobalValue(ServerMeter.AGGREGATE_TIMES_GROUPS_TRIMMED,
1);
+ IndexedTable trimmedTable =
+ buildIndexedTableFromRecords(groupingSetsSchema, queryContext, kept,
executorService);
+ // Surface the approximation: groups were dropped on the server, so the
merged block (and ultimately the
+ // broker response) must be flagged as trimmed.
+ trimmedTable.markTrimmed();
+ return trimmedTable;
+ }
+ return derivedTable;
+ }
+
+ /// Builds a trim-disabled grouping-set [IndexedTable] pre-populated with
the given (already unique) records.
+ /// Used to materialize the per-set-trim survivors back into the table the
combine returns.
+ private static IndexedTable buildIndexedTableFromRecords(DataSchema
dataSchema, QueryContext queryContext,
+ List<IntermediateRecord> records, ExecutorService executorService) {
+ int numRecords = records.size();
+ int initialCapacity =
+ getIndexedTableInitialCapacity(numRecords, numRecords,
queryContext.getMinInitialIndexedTableCapacity());
+ // Populated single-threaded, so use a plain-HashMap-backed table
(numThreads = 1).
+ IndexedTable table = getTrimDisabledIndexedTable(dataSchema, false,
queryContext, Integer.MAX_VALUE,
+ initialCapacity, 1, executorService);
+ for (IntermediateRecord record : records) {
+ table.upsert(record._key, record._record);
+ }
+ return table;
+ }
+
+ /// One derive task: projects every base group into the grouping sets owned
by `taskIndex` (set `s` is owned
+ /// when `s % numTaskSlots == taskIndex`) and aggregates the derived groups
into a task-local map. Each task
+ /// runs single-threaded over its own map, so a plain HashMap suffices; task
key spaces are disjoint because
+ /// every derived key ends with its set ordinal.
+ ///
+ /// The first record stored for a derived key holds cloned intermediates (it
becomes the group's accumulator,
+ /// mutated by later merges); on merge, OBJECT intermediates from the shared
base group are cloned again so the
+ /// merge can never mutate a base accumulator that other tasks are still
reading. Scalar intermediates are
+ /// immutable and pass through uncloned.
+ private static Map<Key, Record> deriveSets(List<Map.Entry<Key, Record>>
baseEntries, boolean[][] setContains,
+ boolean[] isFullUnionSet, int taskIndex, int numTaskSlots, int
numUnionColumns, int numAggregationFunctions,
+ AggregationFunction[] aggregationFunctions) {
+ int numSets = setContains.length;
+ // A full-union owned set produces exactly one derived group per base
entry, so presize for it (it never
+ // rehashes); tasks owning only coarser sets start small and grow, since
their distinct-group counts are
+ // usually far below the base size and a full-size bucket array per task
would be wasted memory.
+ boolean ownsFullUnionSet = false;
+ for (int s = taskIndex; s < numSets; s += numTaskSlots) {
+ ownsFullUnionSet |= isFullUnionSet[s];
+ }
+ Map<Key, Record> taskMap =
+ ownsFullUnionSet ? new
HashMap<>(HashUtil.getHashMapCapacity(baseEntries.size())) : new HashMap<>();
+ // Flyweight probe: reuse one key buffer for lookups (HashMap.get does not
retain its argument) and copy it
+ // into a fresh array only when inserting a new derived group. Most
projections into coarse sets hit an
+ // existing group, so this avoids a key-array + Key allocation per
projection on the merge path.
+ Object[] probeValues = new Object[numUnionColumns + 1];
+ Key probeKey = new Key(probeValues);
+ int numProjections = 0;
+ for (Map.Entry<Key, Record> baseEntry : baseEntries) {
+ Object[] baseKeys = baseEntry.getKey().getValues();
+ Object[] baseValues = baseEntry.getValue().getValues();
+ for (int s = taskIndex; s < numSets; s += numTaskSlots) {
+ // Keep the derive responsive to query timeout / cancellation and
visible to resource accounting, like
+ // the segment-merge loop in GroupByCombineOperator.
+
QueryThreadContext.checkTerminationAndSampleUsagePeriodically(numProjections++,
"GroupByUtils#deriveSets");
+ boolean[] contains = setContains[s];
+ for (int col = 0; col < numUnionColumns; col++) {
+ probeValues[col] = contains[col] ? baseKeys[col] : null;
+ }
+ probeValues[numUnionColumns] = s;
+ // Full-union sets never see a duplicate key, so skip the probe and
insert blindly. Their records can
+ // also share the base intermediates without cloning: no merge will
ever mutate them (this set never
+ // merges, and every merge into OTHER sets clones its second argument
before use).
+ boolean fullUnion = isFullUnionSet[s];
+ Record existing = fullUnion ? null : taskMap.get(probeKey);
+ if (existing == null) {
+ Object[] keyValues = probeValues.clone();
+ Object[] values = new Object[numUnionColumns + 1 +
numAggregationFunctions];
+ System.arraycopy(keyValues, 0, values, 0, numUnionColumns + 1);
+ for (int i = 0; i < numAggregationFunctions; i++) {
+ Object intermediate = baseValues[numUnionColumns + i];
+ values[numUnionColumns + 1 + i] =
+ fullUnion ? intermediate :
cloneIntermediate(aggregationFunctions[i], intermediate);
+ }
+ taskMap.put(new Key(keyValues), new Record(values));
+ } else {
+ Object[] values = existing.getValues();
+ for (int i = 0; i < numAggregationFunctions; i++) {
+ int valueIndex = numUnionColumns + 1 + i;
+ // The first argument is this set's owned accumulator (mutating it
is safe). The second argument is
+ // cloned because AggregationFunction#merge may RETURN its second
argument as the new accumulator
+ // (e.g. HyperLogLog merge with mismatched sizes), which would
then be mutated by later merges while
+ // other tasks are still reading the shared base intermediate.
+ values[valueIndex] =
AggregationFunctionUtils.merge(aggregationFunctions[i], values[valueIndex],
+ cloneIntermediate(aggregationFunctions[i],
baseValues[numUnionColumns + i]));
+ }
+ }
+ }
+ }
+ return taskMap;
+ }
+
+ private static void cancelAll(List<Future<Map<Key, Record>>> futures) {
+ for (Future<Map<Key, Record>> future : futures) {
+ future.cancel(true);
+ }
+ }
+
+ /// Returns `schema` with a synthetic `$groupingId` INT column inserted at
`index` (after the union group-by
+ /// columns), producing the grouping-set output schema from the
base-grouping schema.
+ private static DataSchema insertGroupingIdColumn(DataSchema baseSchema, int
index) {
+ String[] baseNames = baseSchema.getColumnNames();
+ ColumnDataType[] baseTypes = baseSchema.getColumnDataTypes();
+ int numColumns = baseNames.length + 1;
+ String[] names = new String[numColumns];
+ ColumnDataType[] types = new ColumnDataType[numColumns];
+ System.arraycopy(baseNames, 0, names, 0, index);
+ System.arraycopy(baseTypes, 0, types, 0, index);
+ names[index] = GroupingSets.GROUPING_ID_COLUMN;
+ types[index] = ColumnDataType.INT;
+ System.arraycopy(baseNames, index, names, index + 1, baseNames.length -
index);
+ System.arraycopy(baseTypes, index, types, index + 1, baseTypes.length -
index);
+ return new DataSchema(names, types);
+ }
+
+ /// Returns a defensive copy of an aggregation intermediate result so that a
subsequent
+ /// [AggregationFunction#merge] into a derived grouping-set group cannot
mutate a base group's shared
+ /// accumulator. Scalar (non-OBJECT) intermediates are immutable boxed
values and are returned as-is; `null`
+ /// (nothing aggregated) is the merge identity and needs no copy; OBJECT
accumulators are cloned via the
+ /// function's own serialize/deserialize round-trip.
+ private static Object cloneIntermediate(AggregationFunction
aggregationFunction, Object intermediate) {
+ if (intermediate == null ||
aggregationFunction.getIntermediateResultColumnType() != ColumnDataType.OBJECT)
{
+ return intermediate;
+ }
+ SerializedIntermediateResult serialized =
aggregationFunction.serializeIntermediateResult(intermediate);
Review Comment:
Fixed in 119c437 exactly as you suggested: each OBJECT base intermediate is
now serialized exactly once, on exactly one thread (a pre-pass parallelized by
base-entry range, so no object is shared between pre-pass tasks); derive tasks
read only the immutable bytes and deserialize private copies. This removes the
race (serialize-mutates: TDigest compress, theta/CPC/tuple accumulator flushes)
and also cuts serializations from numSets to 1 per base group. Full-union
(identity) sets still adopt the base objects directly — safe now, since after
the pre-pass no other task touches them. The EXPR_MIN/EXPR_MAX issue is
separate (immutable deserialized intermediates, fails even single-threaded) and
is handled by excluding them from the base path via the new
`canMergeIntermediatesAcrossGroups` flag.
##########
pinot-core/src/main/java/org/apache/pinot/core/operator/combine/GroupByCombineOperator.java:
##########
@@ -172,6 +192,36 @@ protected void processSegments() {
}
}
+ private IndexedTable ensureIndexedTable(GroupByResultsBlock resultsBlock) {
+ IndexedTable indexedTable = _indexedTable;
+ if (indexedTable == null) {
+ synchronized (this) {
+ indexedTable = _indexedTable;
+ if (indexedTable == null) {
+ indexedTable =
GroupByUtils.createIndexedTableForCombineOperator(resultsBlock, _queryContext,
_numTasks,
+ _executorService);
+ _indexedTable = indexedTable;
+ }
+ }
+ }
+ return indexedTable;
+ }
+
+ private IndexedTable ensureBaseIndexedTable(GroupByResultsBlock
resultsBlock) {
+ IndexedTable baseIndexedTable = _baseIndexedTable;
+ if (baseIndexedTable == null) {
+ synchronized (this) {
+ baseIndexedTable = _baseIndexedTable;
+ if (baseIndexedTable == null) {
+ baseIndexedTable =
GroupByUtils.createIndexedTableForCombineOperator(resultsBlock, _queryContext,
_numTasks,
Review Comment:
Fixed in 119c437 with your first suggestion: the base combine table (new
`GroupingSetsBaseIndexedTable`) RETAINS records whose new base key arrives
after the `numGroupsLimit` cap in a bounded overflow buffer instead of dropping
them, and `mergeResults` folds them into the already-derived groups (existing
groups only) — the expansion semantics exactly: grand total and coarse
subtotals stay exact, only overflowing fine-set groups are lost, and
`numGroupsLimitReached` is set. If even the buffer overflows (bounded at 10x
numGroupsLimit), the response is additionally flagged `groupsTrimmed`. Added
`testOverflowBaseGroupsKeepTotalsExact` (disjoint per-block key spaces under a
small `numGroupsLimit` → exact grand total); you are right that the earlier
test could not catch this — its segments shared the same 4 keys.
--
This is an automated message from the Apache Git Service.
To respond to the message, please log on to GitHub and use the
URL above to go to the specific comment.
To unsubscribe, e-mail: [email protected]
For queries about this service, please contact Infrastructure at:
[email protected]
---------------------------------------------------------------------
To unsubscribe, e-mail: [email protected]
For additional commands, e-mail: [email protected]
