add release notes 8.5.6

releases/release-8.5.6.md

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+---
+title: TiDB 8.5.6 Release Notes
+summary: 了解 TiDB 8.5.6 版本的兼容性变更、改进提升，以及错误修复。
+---
+
+# TiDB 8.5.6 Release Notes
+
+发版日期：2026 年 x 月 x 日
+
+TiDB 版本：8.5.6
+
+试用链接：[快速体验](https://docs.pingcap.com/zh/tidb/v8.5/quick-start-with-tidb) | [生产部署](https://docs.pingcap.com/zh/tidb/v8.5/production-deployment-using-tiup) | [下载离线包](https://pingkai.cn/download#tidb-community)
+
+## 功能详情
+
+### 性能
+
+- 外键检查支持共享锁（GA） [#66154](https://github.com/pingcap/tidb/issues/66154) @[you06](https://github.com/glorv) **tw@qiancai** <!--2085-->
+
+    对子表进行写入时，支持用户通过设置参数 tidb_foreign_key_check_in_shared_lock 来指定在父表加共享锁实现外键约束检查，相比以前仅支持排它锁，现方案可降低锁冲突提升子表并发写入性能。
+
+    在V8.5.6 中，该功能成为正式功能 (GA)。
+
+    更多信息，请参考[用户文档](/foreign-key.md)。
+
+### 稳定性
+
+- 支持为资源管控的后台任务设置资源上限成为正式功能 (GA) [#56019](https://github.com/pingcap/tidb/issues/56019) @[glorv](https://github.com/glorv) **tw@hfxsd** <!--1933-->
+
+    TiDB 资源管控能够识别并降低后台任务的运行优先级。在部分场景下，即使有空闲资源，用户也希望后台任务消耗能够控制在很低的水平。从 v8.4.0 开始，你可以使用参数 `UTILIZATION_LIMIT` 为资源管控的后台任务设置最大可以使用的资源百分比，每个节点把所有后台任务的使用量控制在这个百分比以下。该功能可以让你精细控制后台任务的资源占用，进一步提升集群稳定性。
+
+    在 v8.5.6 中，该功能成为正式功能 (GA)。
+
+    更多信息，请参考[用户文档](/tidb-resource-control-background-tasks.md)。
+
+### 可观测性
+
+- 支持多维度、多粒度定义慢查询日志的触发规则（GA）[#62959](https://github.com/pingcap/tidb/issues/62959) @[zimulala](https://github.com/zimulala) **tw@lilin90** <!--2068-->
+
+	当前 TiDB 定位慢查询语句的主要方法是设置系统变量 tidb_slow_log_threshold，该机制触发慢日志控制粒度粗（整个实例级别全局控制，不支持会话和SQL级别精细化控制）、触发条件仅执行时间（Query_time）一种，无法满足复杂场景慢日志抓取以精细化定位问题的需求。
+
+	本功能通过设置 tidb_slow_log_rules 系统变量，支持用户在实例、会话、SQL级别定义多维度（如 Query_time、Digest、Mem_max、KV_total 等等）的慢查询日志抓取规则，实现更灵活的精细化控制。
+
+	在 v8.5.6 中，该功能成为正式功能 (GA)。
+
+	更多信息，请参考[用户文档](/identify-slow-queries.md)。
+
+- TOP SQL 增加网络流量和逻辑IO 数据 (GA) [#62916](https://github.com/pingcap/tidb/issues/62916) @[yibin87](https://github.com/yibin87) **tw@qiancai** <!--2398-->
+
+    当前 TiDB TOP SQL 中仅包含 CPU 的相关指标数据，在遇到复杂情况时不利于排查问题。
+
+    本功能在 Top SQL 设置中增加开启 **TiKV 网络I0 采集（多维度）**，方便用户进一步查看指定 TiKV 实例的 Network Bytes、Logical IO Bytes 等指标，并按 By Query、By Table、By DB 或 By Region 维度进行聚合分析。
+
+    在 v8.5.6 中，该功能成为正式功能 (GA)。
+
+    更多信息，请参考 [用户文档](/dashboard/top-sql.md)。
+
+### **SQL**
+
+- Support column-level privilege management [#61706](https://github.com/pingcap/tidb/issues/61706) [@CbcWestwolf](https://github.com/CbcWestwolf),[@fzzf678](https://github.com/fzzf678) **tw@hfxsd** <!--2332-->
+
+    Before v8.5.6, TiDB privilege control mainly covered the database, and table levels, and did not support granting or revoking privileges on specific columns as MySQL does. As a result, when you needed to restrict users to accessing only a subset of sensitive columns in a table, TiDB could not provide sufficiently fine-grained access control.
+
+    Starting from v8.5.6, TiDB supports column-level privilege management. You can use the `GRANT` and `REVOKE` statements to grant or revoke privileges on specific columns, and TiDB performs privilege checks based on column privileges during query processing and execution plan construction. This enables more fine-grained access control and better supports sensitive data isolation and the principle of least privilege.
+
+    For more information, see the [user documentation](/column-privilege-management.md).
+
+ - Support table aliases referenced in the `FOR UPDATE OF` clause [#65532](https://github.com/pingcap/tidb/pull/65532) [@cryo-zd](https://github.com/cryo-zd) **tw@lilin90** <!--2350-->
+
+    Before v8.5.6, when a `SELECT ... FOR UPDATE OF <table>` statement referenced a table alias in the locking clause, TiDB could fail to resolve the alias correctly and return a `table not exists` error even though the alias was valid.
+
+    Starting from v8.5.6, TiDB supports table aliases in the `FOR UPDATE OF` clause. TiDB can now correctly resolve the locking target from the `FROM` clause, including aliased tables, so that row locks are applied as expected. This improves MySQL compatibility and makes `SELECT ... FOR UPDATE OF` statements more reliable in queries that use table aliases.
+
+    For more information, see the user documentation. 
+
+### **DB operations**
+
+- Support specifying the maximum number of nodes for distributed execution tasks [#58937](https://github.com/pingcap/tidb/pull/58937) [@tangenta](https://github.com/tangenta), [@D3Hunter](https://github.com/D3Hunter) **tw@hfxsd** <!--2406-->
+
+    Before v8.5.6, TiDB did not support efficiently limiting how many nodes a distributed execution task could use. When you wanted to control resource usage for distributed task execution, TiDB did not provide a dedicated option to constrain the maximum node count.
+
+    Starting from v8.5.6, TiDB supports the `tidb_max_dist_task_nodes` system variable, which lets you specify the maximum number of TiDB nodes used by a distributed execution task. This gives you more flexibility to manage resource usage and tune distributed task execution based on workload and cluster conditions.
+
+    For more information, see the [user documentation](/system-variables.md#tidb_max_dist_task_nodes-new-in-v856).
+
+### 数据迁移
+
+- (dup): release-9.0.0.md > # 数据迁移 * 将 sync-diff-inspector 从 `pingcap/tidb-tools` 迁移至 `pingcap/tiflow` 代码仓库 [#11672](https://github.com/pingcap/tiflow/issues/11672) @[joechenrh](https://github.com/joechenrh)
+
+## 兼容性变更
+
+对于新部署的 TiDB v8.5.5 集群（即不是从早于 v8.5.4 的版本升级而来的集群），你可以平滑升级到 v8.5.6。v8.5.6 的大多数变更对常规升级是安全的，但也包含了若干行为变更、MySQL 兼容性变更、系统变量变更、配置参数变更以及系统表变更。在升级前，请务必仔细阅读本节内容。
+
+### 行为变更
+
+### MySQL 兼容性
+
+### 系统变量
+
+| 变量名  | 修改类型    | 描述 |
+|--------|------------------------------|------|
+|   |   |   |
+|   |   |   |
+|   |   |   |
+
+### 配置参数
+
+| 配置文件或组件 | 配置项 | 修改类型 | 描述 |
+| -------- | -------- | -------- | -------- |
+|  | |  |
+|  | |  |
+|  | |  |
+
+## 改进提升
+
++ TiDB <!--tw@qiancai: 5 notes-->
+
+    - Improve plan selection for queries with IN predicates on index prefix columns. TiDB can now leverage merge sort to preserve order in ORDER BY ... LIMIT queries, reducing unnecessary scans and improving performance.[#62694](https://github.com/pingcap/tidb/pull/62694) [@time-and-fate](https://github.com/time-and-fate)**tw@hfxsd** <!--2414-->
+    - 增强慢查询日志的控制能力，支持使用 [`tidb_slow_log_rules`](/system-variables.md#tidb_slow_log_rules-从-v900-版本开始引入) 基于多维指标组合条件定向输出慢查询日志，使用 [`tidb_slow_log_max_per_sec`](/system-variables.md#tidb_slow_log_max_per_sec-从-v900-版本开始引入) 限制每秒日志输出数量，并通过 [`WRITE_SLOW_LOG`](/optimizer-hints.md) Hint 强制记录指定 SQL 的慢查询日志 [#64010](https://github.com/pingcap/tidb/issues/64010) @[zimulala](https://github.com/zimulala)
+    - 增强 [Top SQL](/dashboard/top-sql.md) 的资源分析能力，支持展示 Top `5`、`20` 或 `100` 查询，支持按 CPU、网络流量和逻辑 IO 排序查看热点，并支持在 TiKV 实例上按 `Query`、`Table`、`DB` 或 `Region` 维度聚合分析 [#62916](https://github.com/pingcap/tidb/issues/62916) @[yibin87](https://github.com/yibin87)
+    - 新增 DXF 的 max_node_count 配置项支持 [#66376](https://github.com/pingcap/tidb/pull/66376)@[D3Hunter](https://github.com/D3Hunter)
+    - 调整部分 stats 相关日志为 warning 级别 [#58315](https://github.com/pingcap/tidb/pull/58315)@[hawkingrei](https://github.com/hawkingrei)
+    - 调整 tidb_analyze_column_options 默认值为 all [#64992](https://github.com/pingcap/tidb/issues/64992) @[0xPoe](https://github.com/0xPoe)
+
++ TiKV <!--tw@qiancai: 4 notes-->
+
+    - Add MVCC-read-aware load-based compaction to prioritize regions with heavy MVCC read overhead. [#19133](https://github.com/tikv/tikv/issues/19133) @[mittalrishabh](https://github.com/mittalrishabh)
+    - Optimize stale-range cleanup during scaling by deleting stale keys directly instead of ingesting SST files, reducing latency impact. [#18042](https://github.com/tikv/tikv/issues/18042) @[LykxSassinator](https://github.com/LykxSassinator)
+    - Make default gRPC raft connection and concurrency settings scale with CPU quota to improve resource utilization. [#18613](https://github.com/tikv/tikv/issues/18613) @[LykxSassinator](https://github.com/LykxSassinator)
+    - Add Top SQL support for collecting network traffic and logical I/O information to help diagnose SQL performance issues. [#18815](https://github.com/tikv/tikv/issues/18815) @[yibin87](https://github.com/yibin87)
+
++ PD <!--tw@Oreoxmt: 1 note-->
+
+    - 删除不存在的 label 时，现在会返回 404 [#10089](https://github.com/tikv/pd/issues/10089) @[lhy1024](https://github.com/lhy1024)
+    - (dup): release-7.5.7.md > 改进提升> PD - 减少非必要的错误日志 [#9370](https://github.com/tikv/pd/issues/9370) @[bufferflies](https://github.com/bufferflies)
+
++ TiFlash
+
++ Tools
+
+    + Backup & Restore (BR)
+
+    + TiCDC
+
+    + TiDB Data Migration (DM) <!--tw@lilin90: 2 notes-->
+
+        - 新增对 MySQL 8.4 作为 DM 上游数据源的支持，适配该版本引入的新术语和版本检测逻辑 [#11020](https://github.com/pingcap/tiflow/issues/11020) @[dveeden](https://github.com/dveeden)
+        - 在 DM syncer 中新增外键因果依赖支持，确保多 worker 场景下行变更按照父表至子表的外键顺序执行 [#12552](https://github.com/pingcap/tiflow/pull/12552) @[OliverS929](https://github.com/OliverS929)
+
+    + TiDB Lightning
+
+    + Dumpling <!--tw@Oreoxmt: 1 note-->
+
+        - Support exporting data from MySQL 8.4 by adopting the updated MySQL binary log terminology [#53082](https://github.com/pingcap/tidb/issues/53082) @[dveeden](https://github.com/dveeden)
+
+    + TiUP
+
+## 错误修复
+
++ TiDB <!--tw@lilin90: the following 7 notes-->
+
+    - Fix the issue that upgrading from release-8.5-20250606-v8.5.2 to upstream release-8.5 can skip PITR metadata upgrades and cause PITR operations to fail. [#66994](https://github.com/pingcap/tidb/issues/66994) @[fzzf678](https://github.com/fzzf678)
+    - Fix the issue that after EXCHANGE PARTITION, non-unique or nullable unique global indexes on non-clustered partitioned tables can become inconsistent and return incomplete results. [#65289](https://github.com/pingcap/tidb/issues/65289) @[mjonss](https://github.com/mjonss)
+    - Support column-level privileges in GRANT and REVOKE. [#61706](https://github.com/pingcap/tidb/issues/61706) @[CbcWestwolf](https://github.com/CbcWestwolf)
+    - Improve the performance of privilege updates such as GRANT and REVOKE in deployments with large numbers of privilege entries. [#61706](https://github.com/pingcap/tidb/issues/61706) @[CbcWestwolf](https://github.com/CbcWestwolf)
+    - Fix the issue that KILL QUERY incorrectly kills idle connections. [#65447](https://github.com/pingcap/tidb/issues/65447) @[gengliqi](https://github.com/gengliqi)
+    - Fix the issue that column-level privilege checks can be incorrect for JOIN ... USING, NATURAL JOIN, and INSERT ... ON DUPLICATE KEY UPDATE. [#61706](https://github.com/pingcap/tidb/issues/61706) @[CbcWestwolf](https://github.com/CbcWestwolf)
+    - Improve privilege-check performance for deployments with many column-level privilege entries. [#61706](https://github.com/pingcap/tidb/issues/61706) @[CbcWestwolf](https://github.com/CbcWestwolf) <!--tw@hfxsd: the following 8 notes-->
+    - Add cluster_id to mysql.tidb so external tools can determine whether two TiDB instances belong to the same cluster. [#59476](https://github.com/pingcap/tidb/issues/59476) @[YangKeao](https://github.com/YangKeao)
+    - Improve the slow query log by printing non-printable prepared-statement arguments as hexadecimal literals. [#65383](https://github.com/pingcap/tidb/issues/65383) @[dveeden](https://github.com/dveeden)
+    - 修复 tidb_service_scope 设置时未统一转换为小写的问题 [#66835](https://github.com/pingcap/tidb/pull/66835)@[D3Hunter](https://github.com/D3Hunter)
+    - 修复 TiDB 重启后无法展示亲和力表的问题 [#66284](https://github.com/pingcap/tidb/issues/66284) @[lcwangchao](https://github.com/lcwangchao)
+    - 修复可能出现的内存泄漏 [#65522](https://github.com/pingcap/tidb/issues/65522) @[bufferflies](https://github.com/bufferflies)
+    - 修复系统表可能影响 stats healthy 监控的问题 [#64080](https://github.com/pingcap/tidb/issues/64080) @[ti-chi-bot](https://github.com/ti-chi-bot)
+    - 修复 stats delta 数据可能刷新不及时的问题 [#65426](https://github.com/pingcap/tidb/issues/65426) @[ti-chi-bot](https://github.com/ti-chi-bot)
+    - 修复事务中第一条语句使用 fair locking 模式上锁时，有时可能使事务 keep alive 失效、并被意外回滚的问题  [#66571](https://github.com/pingcap/tidb/issues/66571) @[MyonKeminta](https://github.com/MyonKeminta)
+
++ TiKV <!--tw@Oreoxmt: 7 notes-->
+
+    - Fix a memory leak in crossbeam skiplist. [#19285](https://github.com/tikv/tikv/issues/19285) @[ekexium](https://github.com/ekexium)
+    - Fix the issue that global indexes on non-unique columns of partitioned tables might become inconsistent and return incorrect results in some cases. [#19262](https://github.com/tikv/tikv/issues/19262) @[mjonss](https://github.com/mjonss)
+    - Fix the issue that stalled coprocessor snapshot retrieval could occupy unified read pool workers until request deadlines expired, delaying other read requests. [#18491](https://github.com/tikv/tikv/issues/18491) @[AndreMouche](https://github.com/AndreMouche)
+    - Fix the issue that follower replica reads could remain blocked on disk-full TiKV nodes by rejecting read-index requests on disk-full followers. [#19201](https://github.com/tikv/tikv/issues/19201) @[glorv](https://github.com/glorv)
+    - Fix the issue that resolved-ts task backlogs could cause OOM when the resolved-ts worker is busy. [#18359](https://github.com/tikv/tikv/issues/18359) @[overvenus](https://github.com/overvenus)
+    - Fix long-tail follower-read latency during leader transfer by retrying read-index requests sooner and adding a dedicated retry interval setting. [#18417](https://github.com/tikv/tikv/issues/18417) @[gengliqi](https://github.com/gengliqi)
+    - Fix ingest latency spikes in large clusters by increasing the default `rocksdb.max-manifest-file-size` from 128 MiB to 256 MiB. [#18996](https://github.com/tikv/tikv/issues/18996) @[glorv](https://github.com/glorv)
+    - (dup): release-5.1.4.md > Bug 修复> TiKV - 修复悲观事务中 prewrite 请求重试在极少数情况下影响数据一致性的风险 [#11187](https://github.com/tikv/tikv/issues/11187)
+
++ PD <!--tw@hfxsd: 2 notes-->
+
+    - 修复 distribute table sql panic 问题，特别是 merge region operator 比较多的场景容易触发这个 bug。 [#10292](https://github.com/tikv/pd/pull/10292) @[bufferflies](https://github.com/bufferflies)
+    - 修复设置 store limit 后可能不马上生效的问题 [#10108](https://github.com/tikv/pd/issues/10108) @[okJiang](https://github.com/okJiang)
+
++ TiFlash <!--tw@hfxsd: 3 notes-->
+
+    - 修复当一个列执行将列属性 `NOT NULL` 转为 `NULL` 的 DDL 之后，TiFlash 与 TiKV 之间可能产生不一致数据的问题 [#10680](https://github.com/pingcap/tiflash/issues/10680) @[JaySon-Huang](https://github.com/JaySon-Huang)
+    - 修复 Grafana 面板中 Raft throughput 可能会错误地显示一个非常大的数值的问题 [#10701](https://github.com/pingcap/tiflash/issues/10701) @[CalvinNeo](https://github.com/CalvinNeo)
+    - 修复 runtime filter 开启情况下，如果 join key 数据类型不一致时，join 结果可能出错的问题 [#10699](https://github.com/pingcap/tiflash/issues/10699) @[ChangRui-Ryan](https://github.com/ChangRui-Ryan)
+
++ Tools
+
+    + Backup & Restore (BR) <!--tw@lilin90: 4 notes-->
+
+        - 修复 log backup 的 flush_ts 可能为 0 的问题 [#19406](https://github.com/tikv/tikv/issues/19406) @[YuJuncen](https://github.com/YuJuncen)
+        - 修复 BR 在使用 GCP S3 API server 进行 multipart upload 时因缺少 `Content-Length` 头而失败的问题 [#19352](https://github.com/tikv/tikv/issues/19352) @[Leavrth](https://github.com/Leavrth)
+        - 修复 BR `restore point` 可能长时间卡在 `waiting for schema info finishes reloading` 并在 15 分钟后超时失败的问题 [#66110](https://github.com/pingcap/tidb/issues/66110) @[kennytm](https://github.com/kennytm)
+        - 修复 BR 在恢复带有 `SHARD_ROW_ID_BITS`、`PRE_SPLIT_REGIONS` 和 `merge_option` 属性的表时无法正确预分裂 Region 的问题 [#65060](https://github.com/pingcap/tidb/issues/65060) @[JoyC-dev](https://github.com/JoyC-dev)
+
+    + TiCDC <!--tw@Oreoxmt: 4 notes-->
+
+        - 修复了一个在服务器重启时，changefeed 可能会重复创建无效 dispatcher 的问题。[#4452](https://github.com/pingcap/ticdc/issues/4452) @[wlwilliamx](https://github.com/wlwilliamx)
+        - 修复了当 TiDB 版本小于等于 v8.1.x 时，表重命名操作无法正常执行的问题。[#4392](https://github.com/pingcap/ticdc/issues/4392) @[lidezhu](https://github.com/lidezhu)
+        - 修复了一个扫描数据时的 Bug，避免启用 CDC 时 TiKV 可能出现异常崩溃。[#19404](https://github.com/tikv/tikv/issues/19404) @[wk989898](https://github.com/wk989898)
+        - 为 azblob 下游支持 Azure 托管标识认证，并修复了云存储上传过程中可能出现的卡住问题。[#3093](https://github.com/pingcap/ticdc/issues/3093) @[wlwilliamx](https://github.com/wlwilliamx)
+
+    + TiDB Data Migration (DM) <!--tw@qiancai: 3 notes-->
+
+        - 修复 DM 在 binlog rotate 事件时全局 checkpoint 位置未推进的问题 [#12525](https://github.com/pingcap/tiflow/pull/12525) @[OliverS929](https://github.com/OliverS929)
+        - 修复含外键约束的表在 DM safe-mode 下的异常行为，移除 UPDATE 改写中多余的 DELETE 操作并避免触发外键级联 [#12541](https://github.com/pingcap/tiflow/pull/12541) @[OliverS929](https://github.com/OliverS929)
+        - 修复 DM validator 对 UNSIGNED 列误报校验错误的问题 [#12555](https://github.com/pingcap/tiflow/pull/12555) @[OliverS929](https://github.com/OliverS929)
+
+    + TiDB Lightning
+
+    + Dumpling <!--tw@qiancai: 1 note-->
+
+        - 修复 Dumpling 与 MySQL 8.4 的兼容性问题 [#65131](https://github.com/pingcap/tidb/pull/65131) @[dveeden](https://github.com/dveeden)