From cb858f723ceca08be46d1b34aceeafe1a978d7f3 Mon Sep 17 00:00:00 2001 From: yibin Date: Thu, 11 Apr 2024 09:09:22 +0800 Subject: [PATCH] Update fine grained shuffle stream count description (#17114) --- system-variables.md | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/system-variables.md b/system-variables.md index eb1c7a924720d..b42377616b35c 100644 --- a/system-variables.md +++ b/system-variables.md @@ -6025,7 +6025,7 @@ For details, see [Identify Slow Queries](/identify-slow-queries.md). - When the window function is pushed down to TiFlash for execution, you can use this variable to control the concurrency level of the window function execution. The possible values are as follows: * -1: the Fine Grained Shuffle feature is disabled. The window function pushed down to TiFlash is executed in a single thread. - * 0: the Fine Grained Shuffle feature is enabled. If [`tidb_max_tiflash_threads`](/system-variables.md#tidb_max_tiflash_threads-new-in-v610) is set to a valid value (greater than 0), then `tiflash_fine_grained_shuffle_stream_count` is set to the value of [`tidb_max_tiflash_threads`](/system-variables.md#tidb_max_tiflash_threads-new-in-v610). Otherwise, it is set to 8. The actual concurrency level of the window function on TiFlash is: min(`tiflash_fine_grained_shuffle_stream_count`, the number of physical threads on TiFlash nodes). + * 0: the Fine Grained Shuffle feature is enabled. If [`tidb_max_tiflash_threads`](/system-variables.md#tidb_max_tiflash_threads-new-in-v610) is set to a valid value (greater than 0), then `tiflash_fine_grained_shuffle_stream_count` is set to the value of [`tidb_max_tiflash_threads`](/system-variables.md#tidb_max_tiflash_threads-new-in-v610). Otherwise, it is automatically estimated based on the CPU resources of the TiFlash compute node. The actual concurrency level of the window function on TiFlash is: min(`tiflash_fine_grained_shuffle_stream_count`, the number of physical threads on TiFlash nodes). * Integer greater than 0: the Fine Grained Shuffle feature is enabled. The window function pushed down to TiFlash is executed in multiple threads. The concurrency level is: min(`tiflash_fine_grained_shuffle_stream_count`, the number of physical threads on TiFlash nodes). - Theoretically, the performance of the window function increases linearly with this value. However, if the value exceeds the actual number of physical threads, it instead leads to performance degradation.