Environment

• YugabyteDB Anywhere - All Versions

Issue

Customers who have enabled the DocDB cache miss percentage is high alert policy may see alerts for this policy during periods of low or no load.

During a period of low or no load, a compaction may trigger the DocDB cache miss percentage is high alert.

This is because compaction clears the cache. Therefore, whenever compaction occurs for the tablet, the next attempt to read from the tablet will result in a cache miss.

On a Universe with low or no load, any amount of cache misses could constitute a high miss percentage for a given period of time.

Resolution

Overview

Know that the DocDB cache miss percentage is high alert policy is not enabled by default. A user has explicitly enabled it at some point in the past.

Steps

If you and are receiving an alert during periods of no load, and it not impacting the application, consider doing one or more of the following:

• Lowering the Severity of the alert
• Increasing the Duration of the alert
• Increasing the Threshold of the alert
• Disabling the alert

Additional Information

An overview of caching in Yugabyte:

A table is divided into tablets, and each tablet is contains one or more Sorted String Tables (SST) files.

Each SST file is an immutable, sorted file containing key-value pairs. The data is organized into data blocks. Realistically, a block is larger than a single key-value pair, but smaller than a whole SST file.

A certain amount of RAM is used as SST Block Cache. That is, whole blocks are loaded into/unloaded from RAM.

A cache hit corresponds to the event where a SST block is found in RAM and a cache miss corresponds to the event where a SST block is not found in RAM, and the SST block must be read from disk.