all TiDB instance restart with panic due to analyze race

[Lily2025]

Bug Report

Please answer these questions before submitting your issue. Thanks!

1. Minimal reproduce step (Required)

1，run sysbench
2，add and drop column repeatedly

2. What did you expect to see? (Required)

no panic

3. What did you see instead (Required)

all TiDB instance restart with panic when add and drop column
DDL failed due to all tidb instance restart with panic

tidb logs

tidb.log

The immediate cause is
fatal error: concurrent map read and map write
Tidb_build_sampling_stats_concurrency, GetSessionOrGlobalSystemVar related operations
Concurrent analyze worker race on 'SessionVars.systems'

4. What is your TiDB version? (Required)

[2026/05/17 20:20:33.491 +00:00] [INFO] [printer.go:73] ["Welcome to TiDB."] [keyspaceName=10779081037828048042] ["Release Version"=CLOUD.202604.0-abfc4e1aa8] [Edition=Enterprise] ["Git Commit Hash"=abfc4e1aa83d7be98d3defe7f2aa03e6fe76da55] ["Git Branch"=HEAD] ["UTC Build Time"="2026-04-16 08:29:59"] [GoVersion=go1.25.8] ["Race Enabled"=false] ["Check Table Before Drop"=false] ["TiDB Component Version"=v26.4.0-abfc4e1aa8] ["Kernel Type"="Next Generation"] ["Enterprise Extension Commit Hash"=dc633aae52eb11b4e3549e3a7ef5b0ed14e159b1]

[Lily2025]

/severity major

[Lily2025]

/assign qw4990

[mjonss]

Indeed it looks like a race in GetSessionOrGlobalSystemVar:

  if _, ok := s.systems[sv.Name]; !ok {          // line 2950 — read
      if sv.HasGlobalScope() {
          if val, err := s.GlobalVarsAccessor.GetGlobalSysVar(sv.Name); err == nil {
              s.systems[sv.Name] = val           // line 2953 — write
          }
      } else {
          s.systems[sv.Name] = sv.Value           // line 2956 — write
      }
  }

I think the assumption is that it will never be called in parallel for the same SessionVars, but ANALYZE TABLE will create several goroutines which each will check TiDBBuildSamplingStatsConcurrency concurrently, which causes the data race / "fatal error: concurrent map read and map write"