Consider memory during writer scaling #18771

gaurav8297 · 2023-08-22T06:31:20Z

Description

Benchmarks (Unpartitioned)

Before:

trino> set session query_max_memory_per_node = '3GB';
SET SESSION
trino:insert_demo> insert into lineitem_unpart_2 select * from tpch_sf1000_orc.lineitem;

Query 20230829_001613_00003_7gygv, FAILED, 7 nodes
Splits: 903 total, 16 done (1.77%)
11.32 [36.1M rows, 13.1GB] [3.19M rows/s, 1.16GB/s]

Query 20230829_001613_00003_7gygv failed: Query exceeded per-node memory limit of 3GB [Allocated: 3.00GB, Delta: 1010.93kB, Top Consumers: {TableScanOperator=2.51GB, TableWriterOperator=503.44MB, AggregationOperator=115.58kB}]

After:

trino> set session query_max_memory_per_node = '3GB';
SET SESSION
trino:insert_demo> insert into lineitem_unpart select * from tpch_sf1000_orc.lineitem;
INSERT: 5999989709 rows

Query 20230828_224641_00005_ftzqd, FINISHED, 7 nodes
Splits: 3,116 total, 3,116 done (100.00%)
8:52 [6B rows, 172GB] [11.3M rows/s, 330MB/s]

Benchmarks (Partitioned)

Before:

trino:insert_demo> set session query_max_memory_per_node = '6GB';
SET SESSION
trino:insert_demo> insert into lineitem_few_skewed_partitions select orderkey, partkey, suppkey, linenumber, quant
ity, extendedprice, discount, tax, returnflag, linestatus, commitdate, receiptdate, shipinstruct, comment, shipdat
e, shipmode from tpch_sf1000_orc_part.lineitem;

Query 20230831_032052_00012_tus9r, FAILED, 7 nodes
Splits: 1,779 total, 48 done (2.70%)
21.84 [196M rows, 17.3GB] [8.97M rows/s, 811MB/s]

Query 20230831_032052_00012_tus9r failed: Query exceeded per-node memory limit of 6GB [Allocated: 6.00GB, Delta: 3.00MB, Top Consumers: {ScanFilterAndProjectOperator=3.18GB, TableWriterOperator=2.35GB, PagePartitioner=454.33MB}]

After:

trino:insert_demo> set session query_max_memory_per_node = '6GB';
SET SESSION
trino:insert_demo> insert into lineitem_few_skewed_partitions select orderkey, partkey, suppkey, linenumber, quant
ity, extendedprice, discount, tax, returnflag, linestatus, commitdate, receiptdate, shipinstruct, comment, shipdat
e, shipmode from tpch_sf1000_orc_part.lineitem;
INSERT: 5999989709 rows

Query 20230831_031245_00014_dhrst, FINISHED, 7 nodes
Splits: 5,463 total, 5,463 done (100.00%)
11:48 [6B rows, 159GB] [8.48M rows/s, 230MB/s]

However, note that this query takes ~4 minutes with 64GB query_max_memory_per_node.

Additional context and related issues

Release notes

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( ) Release notes are required. Please propose a release note for me.
( ) Release notes are required, with the following suggested text:

# Section
* Fix some things. ({issue}`issuenumber`)

sopel39 · 2023-08-25T15:15:26Z

core/trino-main/src/main/java/io/trino/operator/exchange/LocalExchange.java

 import static java.util.Objects.requireNonNull;
 import static java.util.function.Function.identity;

 @ThreadSafe
 public class LocalExchange
 {
    private static final int SCALE_WRITERS_MAX_PARTITIONS_PER_WRITER = 128;
+    public static final double SCALE_WRITERS_MAX_MEMORY_RATIO = 0.7;


maybe 0.2, 0.5? IMO the totalMemoryUsed should be pretty accurate during scaling up, because the writers are supposed to be full

This should account for how many writers we can add up in single iteration (e.g. scale by 2x, 1.5x)?

core/trino-main/src/main/java/io/trino/operator/output/SkewedPartitionRebalancer.java

core/trino-main/src/main/java/io/trino/operator/exchange/ScaleWriterExchanger.java

core/trino-main/src/main/java/io/trino/execution/scheduler/ScaledWriterScheduler.java

core/trino-main/src/main/java/io/trino/execution/SqlTask.java

core/trino-main/src/main/java/io/trino/execution/TaskStatus.java

core/trino-main/src/main/java/io/trino/execution/scheduler/ScaledWriterScheduler.java

core/trino-main/src/main/java/io/trino/execution/TaskManagerConfig.java

raunaqmorarka · 2023-08-28T04:36:20Z

core/trino-main/src/main/java/io/trino/execution/TaskManagerConfig.java

    // because preferred write partitioning is always enabled for local exchange thus partitioned inserts will never
    // use this property. Hence, there is no risk in terms of more numbers of physical writers which can cause high
    // resource utilization.
-    private int scaleWritersMaxWriterCount = min(getAvailablePhysicalProcessorCount(), 32);
+    private int scaleWritersMaxWriterCount = min(getAvailablePhysicalProcessorCount(), 32) * 2;


Commit message says same value as the number of worker threads, but maxWorkerThreads is Runtime.getRuntime().availableProcessors() * 2 which is a different number

@sopel39 Should we set this to the same number? I think it makes sense in case there are more cores.

sopel39

I think it's fine, but it becomes pretty sophisticated.

I was thinking about something simpler, like task.scale-writers.rebalace-multiplier=2 where we essentially can multiply partition writers up to a factor (decided by user)

core/trino-main/src/main/java/io/trino/sql/planner/LocalExecutionPlanner.java

core/trino-main/src/main/java/io/trino/operator/output/SkewedPartitionRebalancer.java

core/trino-main/src/main/java/io/trino/SystemSessionProperties.java

sopel39 · 2023-09-01T16:01:37Z

core/trino-main/src/main/java/io/trino/execution/TaskManagerConfig.java

-    // use this property. Hence, there is no risk in terms of more numbers of physical writers which can cause high
-    // resource utilization.
-    private int scaleWritersMaxWriterCount = min(getAvailablePhysicalProcessorCount(), 32);
+    // Set the value of default max writer count to the number of processors * 2 and cap it to 64. We can set this value


as discussed we might simplify properties:

min-writer-count max-writer-count scale-writers.enabled

(remove partition writer count)

I'm creating another PR for this

#19135 @sopel39

core/trino-main/src/main/java/io/trino/operator/output/SkewedPartitionRebalancer.java

core/trino-main/src/main/java/io/trino/sql/planner/LocalExecutionPlanner.java

core/trino-main/src/test/java/io/trino/operator/output/TestSkewedPartitionRebalancer.java

core/trino-main/src/main/java/io/trino/SystemSessionProperties.java

core/trino-main/src/main/java/io/trino/operator/exchange/LocalExchange.java

If we don't reset then it's possible that an unskewed partition gets scaled eventually since partitionDataSizeSinceLastRebalance gets accumulated over multiple rebalance cycles. This causes unnecessary partitions to get overscaled which can lead to high memory usage.

This session property specifies the minimum data processed to trigger skewed partition rebalancing in local and remote exchange. Currently, the value of this property is too small and since now we do not work with physicalWrittenBytes in scaling, we can increase the value of this property. This will also make scaling a bit less aggressive.

sopel39

lgtm % comments

core/trino-main/src/main/java/io/trino/operator/exchange/LocalExchange.java

core/trino-main/src/main/java/io/trino/operator/output/SkewedPartitionRebalancer.java

core/trino-main/src/main/java/io/trino/sql/planner/LocalExecutionPlanner.java

sopel39 · 2023-09-19T08:19:29Z

core/trino-main/src/main/java/io/trino/sql/planner/LocalExecutionPlanner.java

@@ -581,10 +585,14 @@ public LocalExecutionPlan plan(
        int taskCount = getTaskCount(partitioningScheme);
        if (checkCanScalePartitionsRemotely(taskContext.getSession(), taskCount, partitioningScheme.getPartitioning().getHandle(), nodePartitioningManager)) {
            partitionFunction = createPartitionFunction(taskContext.getSession(), nodePartitioningManager, partitioningScheme, partitionChannelTypes);
+            // Consider memory while calculating the number of writers. This is to avoid creating too many task buckets.
+            int partitionedWriterCount = min(


just comment: we kind of have no visibility into partitionedWriterCount.

I mean that it's value that is computed internally, but user isn't really aware how big it is. Hence it could potentially be suprising.

core/trino-main/src/main/java/io/trino/sql/planner/LocalExecutionPlanner.java

core/trino-main/src/main/java/io/trino/util/MoreMath.java

Add maxRebalancedPartitions limit to SkewedPartitionRebalancer such that in extreme cases we don't do over scaling which can cause high memory utilization. The value of maxRebalancedPartitions is calculated using max memory allowed per node.

Since writers are both CPU and IO bound, we should increase them to the same value as the number of worker threads.

core/trino-main/src/main/java/io/trino/operator/exchange/LocalExchange.java

sopel39 · 2023-09-25T11:31:40Z

merged, thanks!

sopel39 · 2023-09-25T11:41:14Z

core/trino-main/src/main/java/io/trino/operator/output/SkewedPartitionRebalancer.java

+    public static int getScaleWritersMaxSkewedPartitions(Session session)
+    {
+        // Set the value of maxSkewedPartitions to scale to 60% of maximum number of writers possible per node.
+        return (int) (ceil((double) getQueryMaxMemoryPerNode(session).toBytes() / MAX_MEMORY_PER_PARTITION_WRITER) * 0.60);


nit: comment where 60% came from.

sopel39 · 2023-09-25T11:42:37Z

core/trino-main/src/main/java/io/trino/operator/exchange/LocalExchange.java

+                    // Keep the maxPartitionsToRebalance to atleast writer count such that single partition writes do
+                    // not suffer from skewness and can scale uniformly across all writers. Additionally, note that
+                    // maxWriterCount is calculated considering memory into account. So, it is safe to set the
+                    // maxPartitionsToRebalance to maximum number of writers.


So, it is safe to set the maxPartitionsToRebalance to maximum number of writers.

That kind of depends on order whether you will scale first or see all partitions first.

sopel39 · 2023-09-25T11:47:23Z

core/trino-main/src/main/java/io/trino/sql/planner/LocalExecutionPlanner.java

@@ -3497,24 +3503,29 @@ private int getWriterCount(Session session, WriterScalingOptions connectorScalin
                return 1;
            }

+            int maxWritersBasedOnMemory = getMaxPartitionWritersBasedOnMemory(session);


nit: just getMaxWritersBasedOnMemory

sopel39 · 2023-09-25T11:49:12Z

core/trino-main/src/main/java/io/trino/sql/planner/LocalExecutionPlanner.java

            if (partitioningScheme.isPresent()) {
                // The default value of partitioned writer count is 32 which is high enough to use it
                // for both cases when scaling is enabled or not. Additionally, it doesn't lead to too many
                // small files since when scaling is disabled only single writer will handle a single partition.
+                int partitionedWriterCount = getTaskWriterCount(session);


Shouldn't it be getTaskPartitionedWriterCount as it was getTaskPartitionedWriterCount(session) before? This is unpartitioned, unscaled case.

sopel39 · 2023-09-25T13:45:50Z

core/trino-main/src/main/java/io/trino/sql/planner/LocalExecutionPlanner.java

                            .map(writerCount -> min(writerCount, getTaskPartitionedWriterCount(session)))
                            .orElse(getTaskPartitionedWriterCount(session));
                }
-                return getTaskPartitionedWriterCount(session);
+                // Consider memory while calculating writer count.


you could extract min(partitionedWriterCount, previousPowerOfTwo(maxWritersBasedOnMemory)) and use it here and in plan method. Then it would be obvious it's same thing and where it comes from

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gaurav8297 force-pushed the scale_writer_max_memory branch from d5a3407 to 4d2b7fd Compare August 24, 2023 03:52

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gaurav8297 changed the title ~~Consider memory during scaling~~ Consider memory during writer scaling Sep 12, 2023

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gaurav8297 added 2 commits September 23, 2023 13:39

Refactor SkewedPartitionRebalancer

9629d20

Add maxRebalancedPartitions limit

9ff2d52

Add maxRebalancedPartitions limit to SkewedPartitionRebalancer such that in extreme cases we don't do over scaling which can cause high memory utilization. The value of maxRebalancedPartitions is calculated using max memory allowed per node.

gaurav8297 force-pushed the scale_writer_max_memory branch from 7999410 to 8adfdf7 Compare September 23, 2023 20:54

gaurav8297 added 2 commits September 23, 2023 16:56

Consider maxMemoryPerNode during writer scaling

3a30166

Set value of writerCount to availableProcessors * 2

ce62b56

Since writers are both CPU and IO bound, we should increase them to the same value as the number of worker threads.

gaurav8297 force-pushed the scale_writer_max_memory branch from 8adfdf7 to ce62b56 Compare September 23, 2023 20:56

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sopel39 merged commit 8bba6ff into trinodb:master Sep 25, 2023

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Release notes for 427 #18939

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Simplify writer count properties #19135

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Consider memory during writer scaling #18771

Consider memory during writer scaling #18771

gaurav8297 commented Aug 22, 2023 •

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Consider memory during writer scaling #18771

Consider memory during writer scaling #18771

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gaurav8297 commented Aug 22, 2023 • edited Loading

Description

Benchmarks (Unpartitioned)

Benchmarks (Partitioned)

Additional context and related issues

Release notes

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sopel39 commented Sep 25, 2023

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gaurav8297 commented Aug 22, 2023 •

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