Storage: Improve small partition table read performance by limit concurrency (#10489) by ti-chi-bot · Pull Request #10499 · pingcap/tiflash

ti-chi-bot · 2025-10-23T05:05:08Z

This is an automated cherry-pick of #10489

What problem does this PR solve?

Issue Number: close #10487

Problem Summary:

If a PartitionTableScan involve many partition but each partition only have 1 segment. Then DeltaMergeStore::read will generate num_partitions * num_streams * UnorderedSourceOp. Because there is only 1 segment, SegmentReadTaskPool will only have 1 concurrency for reading data from disk.

tiflash/dbms/src/Storages/DeltaMerge/DeltaMergeStore.cpp

Lines 1421 to 1454 in 80e1927

    
           size_t final_num_stream 
        
               = enable_read_thread ? std::max(1, num_streams) : std::max(1, std::min(num_streams, tasks.size())); 
        
           auto read_mode = getReadMode(db_context, is_fast_scan, keep_order, executor); 
        
           const auto & final_columns_to_read 
        
               = executor && executor->extra_cast ? *executor->columns_after_cast : columns_to_read; 
        
           auto read_task_pool = std::make_shared<SegmentReadTaskPool>( 
        
               extra_table_id_index, 
        
               final_columns_to_read, 
        
               executor, 
        
               start_ts, 
        
               expected_block_size, 
        
               read_mode, 
        
               std::move(tasks), 
        
               after_segment_read, 
        
               log_tracing_id, 
        
               enable_read_thread, 
        
               final_num_stream, 
        
               dm_context->scan_context->keyspace_id, 
        
               dm_context->scan_context->resource_group_name); 
        
           dm_context->scan_context->read_mode = read_mode; 
        
           if (enable_read_thread) 
        
           { 
        
               for (size_t i = 0; i < final_num_stream; ++i) 
        
               { 
        
                   group_builder.addConcurrency(std::make_unique<UnorderedSourceOp>( 
        
                       exec_context, 
        
                       read_task_pool, 
        
                       final_columns_to_read, 
        
                       extra_table_id_index, 
        
                       log_tracing_id, 
        
                       runtime_filter_list, 
        
                       rf_max_wait_time_ms)); 
        
               }

In order to avoid OOM issue when running queries on large PartitionTableScan (#8507), MultiplexInputStream and ConcatBuilderPool will process streams/source ops of partition tables one by one.

tiflash/dbms/src/Operators/ConcatSourceOp.h

Lines 190 to 199 in 80e1927

    
           void add(PipelineExecGroupBuilder & group_builder) 
        
           { 
        
               RUNTIME_CHECK(group_builder.groupCnt() == 1); 
        
               for (size_t i = 0; i < group_builder.concurrency(); ++i) 
        
               { 
        
                   pool[pre_index++].push_back(std::move(group_builder.getCurBuilder(i))); 
        
                   if (pre_index == pool.size()) 
        
                       pre_index = 0; 
        
               } 
        
           }

So there is only 1 concurrency for storage layer scanning data from 1 partition, and all compute thread wait for the blocks read from the partition. Only after the current partition finish reading, compute thread will call streams/source ops from the next partition. It result to the PartitionTableScan performance degrade along with the number of partitions, which is not expected.

What is changed and how it works?

* Limit the number of source ops by num of segment task * 4 in function `DeltaMergeStore::read`. In order to reduce concurrency overhead and let PartitionTableScan with small partitions that only contains 1~2 segments can schedule more segment read tasks in parallel.
  - For large partition, the storage layer still generate `num_streams` * `UnorderedSourceOp`, the behavior is the same as before.
  - For small partition, the storage layer only generate segment task * 4 * `UnorderedSourceOp`. And `ConcatBuilderPool` reorg the source ops and read the data from multiple partitions in parallel
* Introduce `DMReadOptions` and reduce the complexity of adding has_multiple_partitions from compute layer to storage layer.
* Add active_segment_limit, peak_active_segments, block_slot_limit, peak_blocks_in_queue when `SegmentReadTaskPool` finished

Main logic changes is this piece of code: https://github.com/pingcap/tiflash/pull/10489/files#diff-22b900e9e8020dc835612316f3bf151cae28b621bfac64d6a22b377d062f4b7eR1419-R1435

The source ops generated by each partition will be added to ConcatBuilderPool that wrap into ConcatSourceOp. Consider num_stream == 8.

In the master, each partition will generate final_num_stream * UnorderedSourceOp. And ConcatBuilderPool will generate 8 ConcatSourceOp by

ConcatSourceOp on pool[0]: part-1-UnorderedSourceOp, part-2-UnorderedSourceOp, part-3-UnorderedSourceOp
ConcatSourceOp on pool[1]: part-1-UnorderedSourceOp, part-2-UnorderedSourceOp, part-3-UnorderedSourceOp
ConcatSourceOp on pool[2]: part-1-UnorderedSourceOp, part-2-UnorderedSourceOp, part-3-UnorderedSourceOp
ConcatSourceOp on pool[3]: part-1-UnorderedSourceOp, part-2-UnorderedSourceOp, part-3-UnorderedSourceOp
ConcatSourceOp on pool[4]: part-1-UnorderedSourceOp, part-2-UnorderedSourceOp, part-3-UnorderedSourceOp
ConcatSourceOp on pool[5]: part-1-UnorderedSourceOp, part-2-UnorderedSourceOp, part-3-UnorderedSourceOp
ConcatSourceOp on pool[6]: part-1-UnorderedSourceOp, part-2-UnorderedSourceOp, part-3-UnorderedSourceOp
ConcatSourceOp on pool[7]: part-1-UnorderedSourceOp, part-2-UnorderedSourceOp, part-3-UnorderedSourceOp

After this PR, ConcatBuilderPool will generate 8 ConcatSourceOp by

ConcatSourceOp on pool[0]: part-1-UnorderedSourceOp, part-3-UnorderedSourceOp
ConcatSourceOp on pool[1]: part-1-UnorderedSourceOp, part-3-UnorderedSourceOp
ConcatSourceOp on pool[2]: part-1-UnorderedSourceOp, part-3-UnorderedSourceOp
ConcatSourceOp on pool[3]: part-1-UnorderedSourceOp, part-3-UnorderedSourceOp
ConcatSourceOp on pool[4]: part-2-UnorderedSourceOp
ConcatSourceOp on pool[5]: part-2-UnorderedSourceOp
ConcatSourceOp on pool[6]: part-2-UnorderedSourceOp
ConcatSourceOp on pool[7]: part-2-UnorderedSourceOp

So after this PR, compute layer read part-1 and part-2 in parallel

Manual test

manual test of small partition table scan performance as described in #10487 (comment)

-- master
-- we can observe performance regression as the number of partition increased
-- and scanning the same number of rows on partition table is slower than non-partition table
TiDB root@10.2.12.81:test> select "p0-0",count(*) from reports_part partition(p0);
                        -> select "p0-1",count(*) from reports_part partition(p0,p1);
                        -> select "p0-2",count(*) from reports_part partition(p0,p1,p2);
                        -> select "p0-3",count(*) from reports_part partition(p0,p1,p2,p3);
                        -> select "p0-4",count(*) from reports_part partition(p0,p1,p2,p3,p4);
                        -> select "p0-5",count(*) from reports_part partition(p0,p1,p2,p3,p4,p5);
                        -> select "p0-6",count(*) from reports_part partition(p0,p1,p2,p3,p4,p5,p6);
                        -> select "p0-7",count(*) from reports_part partition(p0,p1,p2,p3,p4,p5,p6,p7);
                        -> select "p0-8",count(*) from reports_part partition(p0,p1,p2,p3,p4,p5,p6,p7,p8);
                        -> select "p0-9",count(*) from reports_part partition(p0,p1,p2,p3,p4,p5,p6,p7,p8,p9);
                        -> select "p0-10",count(*) from reports_part partition(p0,p1,p2,p3,p4,p5,p6,p7,p8,p9,p10);
                        -> select "p0-11",count(*) from reports_part partition(p0,p1,p2,p3,p4,p5,p6,p7,p8,p9,p10,p11);
                        -> select "p0-12",count(*) from reports_part partition(p0,p1,p2,p3,p4,p5,p6,p7,p8,p9,p10,p11,p12);
                        -> select "non-part",count(*) from reports;
+------+----------+
| p0-0 | count(*) |
+------+----------+
| p0-0 | 0        |
+------+----------+
1 row in set
Time: 0.025s
+------+----------+
| p0-1 | count(*) |
+------+----------+
| p0-1 | 524288   |
+------+----------+
1 row in set
Time: 0.014s
+------+----------+
| p0-2 | count(*) |
+------+----------+
| p0-2 | 1048576  |
+------+----------+
1 row in set
Time: 0.017s
+------+----------+
| p0-3 | count(*) |
+------+----------+
| p0-3 | 1572864  |
+------+----------+
1 row in set
Time: 0.019s
+------+----------+
| p0-4 | count(*) |
+------+----------+
| p0-4 | 2097152  |
+------+----------+
1 row in set
Time: 0.023s
+------+----------+
| p0-5 | count(*) |
+------+----------+
| p0-5 | 2621440  |
+------+----------+
1 row in set
Time: 0.023s
+------+----------+
| p0-6 | count(*) |
+------+----------+
| p0-6 | 3145728  |
+------+----------+
1 row in set
Time: 0.024s
+------+----------+
| p0-7 | count(*) |
+------+----------+
| p0-7 | 3670016  |
+------+----------+
1 row in set
Time: 0.027s
+------+----------+
| p0-8 | count(*) |
+------+----------+
| p0-8 | 4194304  |
+------+----------+
1 row in set
Time: 0.029s
+------+----------+
| p0-9 | count(*) |
+------+----------+
| p0-9 | 4718592  |
+------+----------+
1 row in set
Time: 0.031s
+-------+----------+
| p0-10 | count(*) |
+-------+----------+
| p0-10 | 5242880  |
+-------+----------+
1 row in set
Time: 0.036s
+-------+----------+
| p0-11 | count(*) |
+-------+----------+
| p0-11 | 5767168  |
+-------+----------+
1 row in set
Time: 0.036s
+-------+----------+
| p0-12 | count(*) |
+-------+----------+
| p0-12 | 6291456  |
+-------+----------+
1 row in set
Time: 0.040s
+----------+----------+
| non-part | count(*) |
+----------+----------+
| non-part | 6291456  |
+----------+----------+
1 row in set
Time: 0.017s

-- after the fix
-- there is no performance regression as the number of partition increased
TiDB root@10.2.12.81:test> select "p0-0",count(*) from reports_part partition(p0);
                        -> select "p0-1",count(*) from reports_part partition(p0,p1);
                        -> select "p0-2",count(*) from reports_part partition(p0,p1,p2);
                        -> select "p0-3",count(*) from reports_part partition(p0,p1,p2,p3);
                        -> select "p0-4",count(*) from reports_part partition(p0,p1,p2,p3,p4);
                        -> select "p0-5",count(*) from reports_part partition(p0,p1,p2,p3,p4,p5);
                        -> select "p0-6",count(*) from reports_part partition(p0,p1,p2,p3,p4,p5,p6);
                        -> select "p0-7",count(*) from reports_part partition(p0,p1,p2,p3,p4,p5,p6,p7);
                        -> select "p0-8",count(*) from reports_part partition(p0,p1,p2,p3,p4,p5,p6,p7,p8);
                        -> select "p0-9",count(*) from reports_part partition(p0,p1,p2,p3,p4,p5,p6,p7,p8,p9);
                        -> select "p0-10",count(*) from reports_part partition(p0,p1,p2,p3,p4,p5,p6,p7,p8,p9,p10);
                        -> select "p0-11",count(*) from reports_part partition(p0,p1,p2,p3,p4,p5,p6,p7,p8,p9,p10,p11);
                        -> select "p0-12",count(*) from reports_part partition(p0,p1,p2,p3,p4,p5,p6,p7,p8,p9,p10,p11,p12);
                        -> select "non-part",count(*) from reports;
+------+----------+
| p0-0 | count(*) |
+------+----------+
| p0-0 | 0        |
+------+----------+
1 row in set
Time: 0.018s
+------+----------+
| p0-1 | count(*) |
+------+----------+
| p0-1 | 524288   |
+------+----------+
1 row in set
Time: 0.011s
+------+----------+
| p0-2 | count(*) |
+------+----------+
| p0-2 | 1048576  |
+------+----------+
1 row in set
Time: 0.013s
+------+----------+
| p0-3 | count(*) |
+------+----------+
| p0-3 | 1572864  |
+------+----------+
1 row in set
Time: 0.012s
+------+----------+
| p0-4 | count(*) |
+------+----------+
| p0-4 | 2097152  |
+------+----------+
1 row in set
Time: 0.012s
+------+----------+
| p0-5 | count(*) |
+------+----------+
| p0-5 | 2621440  |
+------+----------+
1 row in set
Time: 0.013s
+------+----------+
| p0-6 | count(*) |
+------+----------+
| p0-6 | 3145728  |
+------+----------+
1 row in set
Time: 0.013s
+------+----------+
| p0-7 | count(*) |
+------+----------+
| p0-7 | 3670016  |
+------+----------+
1 row in set
Time: 0.014s
+------+----------+
| p0-8 | count(*) |
+------+----------+
| p0-8 | 4194304  |
+------+----------+
1 row in set
Time: 0.015s
+------+----------+
| p0-9 | count(*) |
+------+----------+
| p0-9 | 4718592  |
+------+----------+
1 row in set
Time: 0.014s
+-------+----------+
| p0-10 | count(*) |
+-------+----------+
| p0-10 | 5242880  |
+-------+----------+
1 row in set
Time: 0.017s
+-------+----------+
| p0-11 | count(*) |
+-------+----------+
| p0-11 | 5767168  |
+-------+----------+
1 row in set
Time: 0.014s
+-------+----------+
| p0-12 | count(*) |
+-------+----------+
| p0-12 | 6291456  |
+-------+----------+
1 row in set
Time: 0.017s
+----------+----------+
| non-part | count(*) |
+----------+----------+
| non-part | 6291456  |
+----------+----------+
1 row in set
Time: 0.016s

Check List

Tests

Unit test
Integration test
Manual test (add detailed scripts or steps below)
See the manual test describe above
No code

Side effects

Performance regression: Consumes more CPU
Performance regression: Consumes more Memory
Breaking backward compatibility

Documentation

Release note

Fix the bug that table scan performance on small partition table is not optimal

Signed-off-by: ti-chi-bot <ti-community-prow-bot@tidb.io>

ti-chi-bot · 2025-10-23T05:05:12Z

@JaySon-Huang This PR has conflicts, I have hold it.
Please resolve them or ask others to resolve them, then comment /unhold to remove the hold label.

ti-chi-bot · 2025-10-23T05:05:14Z

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Signed-off-by: JaySon-Huang <tshent@qq.com>

JaySon-Huang · 2025-10-23T06:02:45Z

/unhold

Signed-off-by: JaySon-Huang <tshent@qq.com>

ti-chi-bot · 2025-10-23T07:24:43Z

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: JaySon-Huang, Lloyd-Pottiger

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ti-chi-bot · 2025-10-23T07:24:45Z

[LGTM Timeline notifier]

Timeline:

2025-10-23 06:40:32.377824236 +0000 UTC m=+940338.455076796: ☑️ agreed by Lloyd-Pottiger.
2025-10-23 07:24:44.76906833 +0000 UTC m=+942990.846320890: ☑️ agreed by JaySon-Huang.

This is an automated cherry-pick of pingcap#10489

0b4a8d2

Signed-off-by: ti-chi-bot <ti-community-prow-bot@tidb.io>

ti-chi-bot mentioned this pull request Oct 23, 2025

Storage: Improve small partition table read performance by limit concurrency #10489

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Resolve conflict

42d5a79

Signed-off-by: JaySon-Huang <tshent@qq.com>

JaySon-Huang requested review from CalvinNeo, JinheLin and Lloyd-Pottiger October 23, 2025 06:02

ti-chi-bot bot removed the do-not-merge/hold Indicates that a PR should not merge because someone has issued a /hold command. label Oct 23, 2025

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Fix

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ti-chi-bot bot merged commit 6a8b2c6 into pingcap:release-8.5 Oct 23, 2025
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add v8.5.4 release notes pingcap/docs-cn#21000

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Storage: Improve small partition table read performance by limit concurrency (#10489)#10499

Storage: Improve small partition table read performance by limit concurrency (#10489)#10499
ti-chi-bot[bot] merged 3 commits intopingcap:release-8.5from
ti-chi-bot:cherry-pick-10489-to-release-8.5

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	size_t final_num_stream
	= enable_read_thread ? std::max(1, num_streams) : std::max(1, std::min(num_streams, tasks.size()));
	auto read_mode = getReadMode(db_context, is_fast_scan, keep_order, executor);
	const auto & final_columns_to_read
	= executor && executor->extra_cast ? *executor->columns_after_cast : columns_to_read;
	auto read_task_pool = std::make_shared<SegmentReadTaskPool>(
	extra_table_id_index,
	final_columns_to_read,
	executor,
	start_ts,
	expected_block_size,
	read_mode,
	std::move(tasks),
	after_segment_read,
	log_tracing_id,
	enable_read_thread,
	final_num_stream,
	dm_context->scan_context->keyspace_id,
	dm_context->scan_context->resource_group_name);
	dm_context->scan_context->read_mode = read_mode;

	if (enable_read_thread)
	{
	for (size_t i = 0; i < final_num_stream; ++i)
	{
	group_builder.addConcurrency(std::make_unique<UnorderedSourceOp>(
	exec_context,
	read_task_pool,
	final_columns_to_read,
	extra_table_id_index,
	log_tracing_id,
	runtime_filter_list,
	rf_max_wait_time_ms));
	}

	void add(PipelineExecGroupBuilder & group_builder)
	{
	RUNTIME_CHECK(group_builder.groupCnt() == 1);
	for (size_t i = 0; i < group_builder.concurrency(); ++i)
	{
	pool[pre_index++].push_back(std::move(group_builder.getCurBuilder(i)));
	if (pre_index == pool.size())
	pre_index = 0;
	}
	}

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ti-chi-bot commented Oct 23, 2025

What problem does this PR solve?

What is changed and how it works?

Manual test

Check List

Release note

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