Github user Ben-Zvi commented on a diff in the pull request:
https://github.com/apache/drill/pull/822#discussion_r119736678
--- Diff:
exec/java-exec/src/main/java/org/apache/drill/exec/physical/impl/aggregate/HashAggTemplate.java
---
@@ -266,17 +508,138 @@ public void setup(HashAggregate hashAggrConfig,
HashTableConfig htConfig, Fragme
}
}
- ChainedHashTable ht =
+ spillSet = new SpillSet(context,hashAggrConfig,
UserBitShared.CoreOperatorType.HASH_AGGREGATE);
+ baseHashTable =
new ChainedHashTable(htConfig, context, allocator, incoming, null
/* no incoming probe */, outgoing);
- this.htable = ht.createAndSetupHashTable(groupByOutFieldIds);
-
+ this.groupByOutFieldIds = groupByOutFieldIds; // retain these for
delayedSetup, and to allow recreating hash tables (after a spill)
numGroupByOutFields = groupByOutFieldIds.length;
- batchHolders = new ArrayList<BatchHolder>();
- // First BatchHolder is created when the first put request is received.
doSetup(incoming);
}
+ /**
+ * Delayed setup are the parts from setup() that can only be set after
actual data arrives in incoming
+ * This data is used to compute the number of partitions.
+ */
+ private void delayedSetup() {
+
+ // Set the number of partitions from the configuration (raise to a
power of two, if needed)
+ numPartitions =
context.getConfig().getInt(ExecConstants.HASHAGG_NUM_PARTITIONS_KEY);
+ if ( numPartitions == 1 ) {
+ canSpill = false;
+ logger.warn("Spilling was disabled");
+ }
+ while (Integer.bitCount(numPartitions) > 1) { // in case not a power
of 2
+ numPartitions++;
+ }
+ if ( schema == null ) { estMaxBatchSize = 0; } // incoming was an
empty batch
+ else {
+ // Estimate the max batch size; should use actual data (e.g. lengths
of varchars)
+ updateEstMaxBatchSize(incoming);
+ }
+ long memAvail = memoryLimit - allocator.getAllocatedMemory();
+ if ( !canSpill ) { // single phase, or spill disabled by configuation
+ numPartitions = 1; // single phase should use only a single
partition (to save memory)
+ } else { // two phase
+ // Adjust down the number of partitions if needed - when the memory
available can not hold as
+ // many batches (configurable option), plus overhead (e.g. hash
table, links, hash values))
+ while ( numPartitions * ( estMaxBatchSize * minBatchesPerPartition +
8 * 1024 * 1024) > memAvail ) {
+ numPartitions /= 2;
+ if ( numPartitions < 2) {
+ if ( is2ndPhase ) { canSpill = false; } // 2nd phase needs at
least 2 to make progress
+ break;
+ }
+ }
+ }
+ logger.trace("{} phase. Number of partitions chosen: {}. {} spill",
isTwoPhase?(is2ndPhase?"2nd":"1st"):"Single",
+ numPartitions, canSpill ? "Can" : "Cannot");
+
+ // The following initial safety check should be revisited once we can
lower the number of rows in a batch
+ // In cases of very tight memory -- need at least memory to process
one batch, plus overhead (e.g. hash table)
+ if ( numPartitions == 1 ) {
+ // if too little memory - behave like the old code -- no memory
limit for hash aggregate
+ allocator.setLimit(10_000_000_000L);
+ }
+ // Based on the number of partitions: Set the mask and bit count
+ partitionMask = numPartitions - 1; // e.g. 32 --> 0x1F
+ bitsInMask = Integer.bitCount(partitionMask); // e.g. 0x1F -> 5
+
+ // Create arrays (one entry per partition)
+ htables = new HashTable[numPartitions] ;
+ batchHolders = (ArrayList<BatchHolder>[]) new
ArrayList<?>[numPartitions] ;
+ outBatchIndex = new int[numPartitions] ;
+ outputStream = new OutputStream[numPartitions];
+ spilledBatchesCount = new int[numPartitions];
+ // spilledPaths = new Path[numPartitions];
+ spillFiles = new String[numPartitions];
+ spilledPartitionsList = new ArrayList<SpilledPartition>();
+
+ plannedBatches = numPartitions; // each partition should allocate its
first batch
+
+ // initialize every (per partition) entry in the arrays
+ for (int i = 0; i < numPartitions; i++ ) {
+ try {
+ this.htables[i] =
baseHashTable.createAndSetupHashTable(groupByOutFieldIds, numPartitions);
+ this.htables[i].setMaxVarcharSize(maxColumnWidth);
+ } catch (IllegalStateException ise) {} // ignore
+ catch (Exception e) { throw new DrillRuntimeException(e); }
+ this.batchHolders[i] = new ArrayList<BatchHolder>(); // First
BatchHolder is created when the first put request is received.
+ }
+ }
+ /**
+ * get new incoming: (when reading spilled files like an "incoming")
+ * @return The (newly replaced) incoming
+ */
+ @Override
+ public RecordBatch getNewIncoming() { return incoming; }
+
+ private void initializeSetup(RecordBatch newIncoming) throws
SchemaChangeException, ClassTransformationException, IOException {
+ baseHashTable.updateIncoming(newIncoming); // after a spill - a new
incoming
+ this.incoming = newIncoming;
+ nextPartitionToReturn = 0;
+ for (int i = 0; i < numPartitions; i++ ) {
+ htables[i].reinit(newIncoming);
+ if ( batchHolders[i] != null) {
+ for (BatchHolder bh : batchHolders[i]) {
+ bh.clear();
+ }
+ batchHolders[i].clear();
+ batchHolders[i] = new ArrayList<BatchHolder>();
+ }
+ outBatchIndex[i] = 0;
+ outputStream[i] = null;
+ spilledBatchesCount[i] = 0;
+ // spilledPaths[i] = null;
+ spillFiles[i] = null;
+ }
+ }
+
+ /**
+ * Update the estimated max batch size to be used in the Hash Aggr Op.
+ * using the record batch size to get the row width.
+ * @param incoming
+ */
+ private void updateEstMaxBatchSize(RecordBatch incoming) {
+ if ( estMaxBatchSize > 0 ) { return; } // no handling of a schema (or
varchar) change
+ RecordBatchSizer sizer = new RecordBatchSizer(incoming);
+ logger.trace("Incoming sizer: {}",sizer);
+ // An empty batch only has the schema, can not tell actual length of
varchars
+ // else use the actual varchars length, each capped at 50 (to match
the space allocation)
+ estRowWidth = sizer.rowCount() == 0 ? sizer.stdRowWidth() :
sizer.netRowWidthCap50();
+ estMaxBatchSize = estRowWidth * MAX_BATCH_SIZE;
+
+ // Get approx max (varchar) column width to get better memory
allocation
+ maxColumnWidth = Math.max(sizer.maxSize(),
VARIABLE_MIN_WIDTH_VALUE_SIZE);
+ maxColumnWidth = Math.min(maxColumnWidth,
VARIABLE_MAX_WIDTH_VALUE_SIZE);
+
+ logger.trace("{} phase. Estimated row width: {} batch size: {}
memory limit: {} max column width: {}",
+
isTwoPhase?(is2ndPhase?"2nd":"1st"):"Single",estRowWidth,estMaxBatchSize,memoryLimit,maxColumnWidth);
+
+ if ( estMaxBatchSize > memoryLimit ) {
+ logger.warn("HashAggregate: Estimated max batch size {} is larger
than the memory limit {}",estMaxBatchSize,memoryLimit);
--- End diff --
True; this check alerts only of the more extreme cases, where the memory
available initially can not hold even a single batch (easier to explain in a
warning message).
However note that following the execution of this code, there is another
check (in delayedSetup() ) which does add the overhead (as a hard coded 8MB)
and gives another warning alert (when down to 1 partition; this was just added
in a prior review comment; see above).
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