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update docs about logs (#4575) #4773

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Nov 2, 2020
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update docs about logs (#4575) #4773

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12 changes: 10 additions & 2 deletions identify-slow-queries.md
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Original file line number Diff line number Diff line change
Expand Up @@ -14,11 +14,13 @@ TiDB 默认启用慢查询日志，可以修改配置 [`enable-slow-log`](/tidb-
```sql
# Time: 2019-08-14T09:26:59.487776265+08:00
# Txn_start_ts: 410450924122144769
# User: root@127.0.0.1
# User@Host: root[root] @ localhost [127.0.0.1]
# Conn_ID: 3086
# Exec_retry_time: 5.1 Exec_retry_count: 3
# Query_time: 1.527627037
# Parse_time: 0.000054933
# Compile_time: 0.000129729
# Rewrite_time: 0.000000003 Preproc_subqueries: 2 Preproc_subqueries_time: 0.000000002
# Process_time: 0.07 Request_count: 1 Total_keys: 131073 Process_keys: 131072 Prewrite_time: 0.335415029 Commit_time: 0.032175429 Get_commit_ts_time: 0.000177098 Local_latch_wait_time: 0.106869448 Write_keys: 131072 Write_size: 3538944 Prewrite_region: 1
# DB: test
# Is_internal: false
Expand All @@ -36,6 +38,7 @@ TiDB 默认启用慢查询日志，可以修改配置 [`enable-slow-log`](/tidb-
# Plan_from_cache: false
# Succ: true
# Plan: tidb_decode_plan('ZJAwCTMyXzcJMAkyMAlkYXRhOlRhYmxlU2Nhbl82CjEJMTBfNgkxAR0AdAEY1Dp0LCByYW5nZTpbLWluZiwraW5mXSwga2VlcCBvcmRlcjpmYWxzZSwgc3RhdHM6cHNldWRvCg==')
use test;
insert into t select * from t;
```

Expand All @@ -61,6 +64,11 @@ Slow Query 基础信息：
* `Plan`：表示语句的执行计划，用 `select tidb_decode_plan('xxx...')` SQL 语句可以解析出具体的执行计划。
* `Prepared`：表示这个语句是否是 `Prepare` 或 `Execute` 的请求。
* `Plan_from_cache`：表示这个语句是否命中了执行计划缓存。
* `Rewrite_time`：表示这个语句在查询改写阶段花费的时间。
* `Preproc_subqueries`：表示这个语句中被提前执行的子查询个数，如 `where id in (select if from t)` 这个子查询就可能被提前执行。
* `Preproc_subqueries_time`：表示这个语句中被提前执行的子查询耗时。
* `Exec_retry_count`：表示这个语句执行的重试次数。一般出现在悲观事务中，上锁失败时重试执行该语句。
* `Exec_retry_time`：表示这个语句的重试执行时间。例如某个查询一共执行了三次（前两次失败），则 `Exec_retry_time` 表示前两次的执行时间之和，`Query_time` 减去 `Exec_retry_time` 则为最后一次执行时间。

和事务执行相关的字段：

Expand Down Expand Up @@ -113,7 +121,7 @@ Slow Query 基础信息：
* [tidb_slow_log_threshold](/system-variables.md#tidb_slow_log_threshold)：设置慢日志的阈值，执行时间超过阈值的 SQL 语句将被记录到慢日志中。默认值是 300 ms。
* [tidb_query_log_max_len](/system-variables.md#tidb_query_log_max_len)：设置慢日志记录 SQL 语句的最大长度。默认值是 4096 byte。
* [tidb_log_desensitization](/system-variables.md#tidb_log_desensitization)：设置慢日志记录 SQL 时是否将用户数据脱敏用 `?` 代替。默认值是 0 ，即关闭该功能。
* [tidb_enable_collect_execution_info](/system-variables.md#tidb_enable_collect_execution_info)：设置是否记录执行计划中各个算子的执行信息，默认值是 1。该功能对性能的影响约为 3%。开启该项后查看 `Plan` 的示例如下：
* [tidb_enable_collect_execution_info](/system-variables.md#tidb_enable_collect_execution_info)：设置是否记录执行计划中各个算子的物理执行信息，默认值是 `1`。该功能对性能的影响约为 3%。开启该项后查看 `Plan` 的示例如下：

```sql
> select tidb_decode_plan('jAOIMAk1XzE3CTAJMQlmdW5jczpjb3VudChDb2x1bW4jNyktPkMJC/BMNQkxCXRpbWU6MTAuOTMxNTA1bXMsIGxvb3BzOjIJMzcyIEJ5dGVzCU4vQQoxCTMyXzE4CTAJMQlpbmRleDpTdHJlYW1BZ2dfOQkxCXQRSAwyNzY4LkgALCwgcnBjIG51bTogMQkMEXMQODg0MzUFK0hwcm9jIGtleXM6MjUwMDcJMjA2HXsIMgk1BWM2zwAAMRnIADcVyAAxHcEQNQlOL0EBBPBbCjMJMTNfMTYJMQkzMTI4MS44NTc4MTk5MDUyMTcJdGFibGU6dCwgaW5kZXg6aWR4KGEpLCByYW5nZTpbLWluZiw1MDAwMCksIGtlZXAgb3JkZXI6ZmFsc2UJMjUBrgnQVnsA');
Expand Down