slow log no user

## Bug Report

Please answer these questions before submitting your issue. Thanks!

### 1. Minimal reproduce step (Required)

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

### 3. What did you see instead (Required)
```
# Time: 2026-03-16T07:59:28.942601954Z
# Txn_start_ts: 464951173057609888
# Keyspace_name: MDXv1i7V9xxxxx
# Keyspace_ID: 80000
# Query_time: 0.385883279
# Parse_time: 0
# Compile_time: 0.000211202
# Rewrite_time: 0.000038341
# Optimize_time: 0.000092026
# Wait_TS: 0.000298231
# Cop_time: 0.385132088 Process_time: 0.000076819 Wait_time: 0.380681297 Request_count: 1 Process_keys: 1 Total_keys: 2 Get_snapshot_time: 0.000
# Index_names: [tidb:PRIMARY]
# Is_internal: false
# Is_tiflash: false
# Digest: 19f86abc604ef6ca71b7d66d6d7eaa6629284af50fe51fb42a468ecf9ddce872
# Stats: tidb:pseudo[10000;0]
# Num_cop_tasks: 1
# Cop_proc_avg: 7.6819e-05 Cop_proc_addr: tikv-i7i4xlarge-31v250627-p3-tikv-1.tikv-i7i4xlarge-31v250627-p3-tikv-peer.tidb-serverless.svc:20160
# Cop_wait_avg: 0.380681297 Cop_wait_addr: tikv-i7i4xlarge-31v250627-p3-tikv-1.tikv-i7i4xlarge-31v250627-p3-tikv-peer.tidb-serverless.svc:20160
# Mem_max: 278
# Prepared: false
# Plan_from_cache: false
# Plan_from_binding: false
# Has_more_results: false
# KV_total: 0
# PD_total: 0
# Backoff_total: 0
# Write_sql_response_total: 0
# Result_rows: 1
# Succ: true
# IsExplicitTxn: false
# IsSyncStatsFailed: false
# Plan: tidb_decode_plan('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')
# Plan_digest: d08b69dd675b721c4057e3e0d054f1fdfe2de3f3dfb26be812792f32d3910162
# Binary_plan: tidb_decode_binary_plan('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')
# Resource_group: default
# Tikv_cpu_time: 0.000076819
# Serverless_cluster_ID: 10606699983184926324
# Serverless_project_ID: 1372813089454575345
# Serverless_tenant_ID: 1372813089209251856
select `variable_name` from `mysql` . `tidb` limit ?;
```

### 4. What is your TiDB version? (Required)