Note:
This topic has been translated from a Chinese forum by GPT and might contain errors.Original topic: ask tiflash|关于参数 tidb_max_tiflash_threads 的疑问
|
username: BigC
[TiDB Usage Environment]
Production Environment
[TiDB Version]
6.5.0
[Reproduction Path]
N/A
[Encountered Problem: Problem Phenomenon and Impact]
TiFlash 性能调优 | PingCAP 文档中心
The execution plan contains the following content:
mysql> explain analyze select a, count(*) from t group by a;
±-------------------------------------±-------------±----------±-------------±--------------±-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------±-----------------------------------------------------------------------------------------------------------------------------±-------±-----+
| id | estRows | actRows | task | access object | execution info | operator info | memory | disk |
±-------------------------------------±-------------±----------±-------------±--------------±-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------±-----------------------------------------------------------------------------------------------------------------------------±-------±-----+
| TableReader_44 | 20.00 | 20 | root | | time:655.9ms, loops:2, cop_task: {num: 14, max: 0s, min: 0s, avg: 0s, p95: 0s, copr_cache_hit_ratio: 0.00} | data:ExchangeSender_43 | N/A | N/A |
| └─ExchangeSender_43 | 20.00 | 20 | mpp[tiflash] | | tiflash_task:{proc max:654.6ms, min:652.4ms, avg: 653.8ms, p80:654.6ms, p95:654.6ms, iters:11, tasks:3, threads:24} | ExchangeType: PassThrough | N/A | N/A |
| └─Projection_5 | 20.00 | 20 | mpp[tiflash] | | tiflash_task:{proc max:654.3ms, min:651.4ms, avg: 653.1ms, p80:654.3ms, p95:654.3ms, iters:11, tasks:3, threads:24} | test.t.a, Column#22 | N/A | N/A |
| └─Projection_39 | 20.00 | 20 | mpp[tiflash] | | tiflash_task:{proc max:654.3ms, min:651.4ms, avg: 653.1ms, p80:654.3ms, p95:654.3ms, iters:11, tasks:3, threads:24} | Column#22, test.t.a | N/A | N/A |
| └─HashAgg_40 | 20.00 | 20 | mpp[tiflash] | | tiflash_task:{proc max:654.3ms, min:651.4ms, avg: 653.1ms, p80:654.3ms, p95:654.3ms, iters:11, tasks:3, threads:24} | group by:test.t.a, funcs:sum(Column#29)->Column#22, funcs:firstrow(test.t.a)->test.t.a, stream_count: 8 | N/A | N/A |
| └─ExchangeReceiver_42 | 20.00 | 60 | mpp[tiflash] | | tiflash_task:{proc max:654.3ms, min:651.4ms, avg: 653.1ms, p80:654.3ms, p95:654.3ms, iters:11, tasks:3, threads:24} | stream_count: 8 | N/A | N/A |
| └─ExchangeSender_41 | 20.00 | 60 | mpp[tiflash] | | tiflash_task:{proc max:649ms, min:0s, avg: 216.3ms, p80:649ms, p95:649ms, iters:3, tasks:3, threads:24} | ExchangeType: HashPartition, Hash Cols: [name: test.t.a, collate: binary], stream_count: 8 | N/A | N/A |
| └─HashAgg_37 | 20.00 | 60 | mpp[tiflash] | | tiflash_task:{proc max:649ms, min:0s, avg: 216.3ms, p80:649ms, p95:649ms, iters:3, tasks:3, threads:24} | group by:test.t.a, funcs:count(1)->Column#29 | N/A | N/A |
| └─TableFullScan_26 | 600000000.00 | 600000000 | mpp[tiflash] | table:t | tiflash_task:{proc max:40ms, min:0s, avg: 13.3ms, p80:40ms, p95:40ms, iters:9386, tasks:3, threads:24}, tiflash_scan:{dtfile:{total_scanned_packs:73833, total_skipped_packs:174, total_scanned_rows:600000000, total_skipped_rows:1402537, total_rs_index_load_time: 0ms, total_read_time: 4ms}, total_create_snapshot_time: 0ms} | keep order:false | N/A | N/A |
±-------------------------------------±-------------±----------±-------------±--------------±-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------±-----------------------------------------------------------------------------------------------------------------------------±-------±-----+
9 rows in set (0.67 sec)
Questions:
- Does tasks:3 mean that this SQL query has 3 TiFlash tasks? Based on what is it split into 3?
- threads:24, when tidb_max_tiflash_threads is set to 24, does this mean that the maximum number of MPP task threads used is 24, or is there another algorithm? The above document just happens to have threads: and tidb_max_tiflash_threads set to the same value?
[Resource Configuration]
N/A
[Attachments: Screenshots/Logs/Monitoring]
N/A
|
username: