Request to add graph for InnoDB History List Length to CloudWatch Metrics for RDS MySQL Databases

Question

The InnoDB History List Length is an important metric to monitor to ensure that Disk I/O is sufficient for an instance.  See [Baron Schwartz excellent article](https://orangematter.solarwinds.com/2015/07/20/what-is-innodb-history-list-length/) about what it is.

When the InnoDB purge process is not able to keep up, it can lead to very unexpected behavior, such as otherwise unexplainable high disk I/O, and slow performance. [example](https://repost.aws/questions/QUGwYpYuhVRymUcRacwT1QQw/the-innodb-history-list-length-increased-significantly)

It would be useful for the community to have this metric monitored automatically with CloudWatch for all MySQL instances.  You can obtain the value easily with the command

```
SELECT count
FROM information_schema.innodb_metrics
WHERE name = 'trx_rseg_history_len'
```

Since InnoDB is the default storage engine on MySQL and Aurora/MySQL instances, this would help customer understand if their write capacity is insufficient, and provide a starting point for investigating more complex issues.

Accepted Answer

You can get the specific metric using Performance Insights, if you enabled Performance insights for the RDS MySQL instances there are multiple [Non-native counters for Amazon RDS for MariaDB and MySQL](https://docs.aws.amazon.com/AmazonRDS/latest/UserGuide/USER_PerfInsights_Counters.html#USER_PerfInsights_Counters.MySQL.NonNative) which are supported.

Checking the link attached it also supports **trx_rseg_history_len**.

On an added Note: 
Performance Insights offers a rolling seven days of performance data history at no charge. This is enough time to troubleshoot a wide variety of issues. The Performance Insights free tier includes:
   *  7 days of performance data history
   * 1 million API requests per month
   
Hope it helps and if it does, I would appreciate if answer can be accepted so that community can benefit for clarity when searching for similar enquirers in Repost, thank you ;)

Request to add graph for InnoDB History List Length to CloudWatch Metrics for RDS MySQL Databases

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