From 80d31cceb051e15462065c440b2e34154ccb8b8d Mon Sep 17 00:00:00 2001 From: Mattias Jonsson Date: Sat, 8 Aug 2026 11:10:24 +0100 Subject: [PATCH] system-variables: mark tidb_merge_partition_stats_concurrency as deprecated Global stats merging no longer runs the TopN merge concurrently, so the variable has no effect. It is kept for backward compatibility: setting it to a value other than 1 returns a warning, and both read paths return 1 unconditionally, so a non-1 value persisted by an earlier TiDB does not survive an upgrade. ref pingcap/tidb#68147 --- system-variables.md | 4 ++++ 1 file changed, 4 insertions(+) diff --git a/system-variables.md b/system-variables.md index 1555a6ceb02e6..cff247bb5a190 100644 --- a/system-variables.md +++ b/system-variables.md @@ -4263,6 +4263,10 @@ For a system upgraded to v5.0 from an earlier version, if you have not modified ### tidb_merge_partition_stats_concurrency +> **Warning:** +> +> Starting from v9.0.0, this variable is deprecated. Merging TopN results of partitioned tables no longer runs concurrently, so this variable has no effect. Setting it to a value other than `1` returns a warning, and reading it always returns `1`, including on clusters upgraded from an earlier version where a different value was persisted. + - Scope: SESSION | GLOBAL - Persists to cluster: Yes - Applies to hint [SET_VAR](/optimizer-hints.md#set_varvar_namevar_value): No