Querying Big Keys and Hot Keys in a DCS Redis Instance

Notes and Constraints

Notes on big key analysis:

• During big key analysis, all keys will be traversed. The larger the number of keys, the longer the analysis takes.
• Perform big key analysis during off-peak hours and avoid automatic backup periods.
• For a master/standby, read/write splitting, or cluster instance, the big key analysis is performed on the standby node, so the impact on the instance is minor. For a single-node instance, the big key analysis is performed on the only node of the instance and will reduce the instance access performance.
• A maximum of 100 analysis records are retained for each instance. When this limit is reached, the oldest records will be deleted to make room for new records. You can also manually delete records you no longer need.

Notes on hot key analysis:

• The maxmemory-policy parameter of the instance must be set to allkeys-lfu or volatile-lfu.
• During hot key analysis, all keys will be traversed. The larger the number of keys, the longer the analysis takes.
• Perform hot key analysis shortly after peak hours to ensure the accuracy of the analysis results.
• The hot key analysis is performed on the master node of each instance and will reduce the instance access performance.
• A maximum of 100 hot key analysis records are retained for each instance. When this limit is reached, the oldest records will be deleted to make room for new records. You can also manually delete records you no longer need.

Big key and hot key analysis consumes CPU. Perform big key and hot key analysis during off-peak hours to avoid 100% CPU usage.

Querying Big Keys

1. Log in to the management console, and choose Application > Distributed Cache Service in the service list.
2. Click in the upper left corner of the management console and select the region where your instance is located.
3. In the navigation pane, choose Cache Manager.
4. Click the name of a DCS Redis instance.
5. Choose Analysis and Diagnosis > Cache Analysis.
6. On the Big Key Analysis tab page, you can manually start a big key analysis or schedule a daily automatic analysis.
7. After an analysis task completes, click View to view the analysis results of different data types.

   You can also click Download or Delete in the Operation column to download or delete the analysis result.

   

   The big key analysis result shows records of the top 100 (20 for Strings and 80 for Lists/Sets/Zsets/Hashes) data size.

   Figure 1 Viewing the results of big key analysis (for Strings)
   
   Figure 2 Viewing the results of big key analysis (for Lists/Sets/Zsets/Hashes)
   

   Table 1 Results of big key analysis

   Parameter	Description
   Key	The key name in a big key analysis result.
   Type	Type of a key, which can be string, hash, list, set, or zset.
   Size	The value size of a key, in Bytes.
   Quantity	Number of elements in a key. This parameter is displayed only for list, set, zset, or hash type. Unit: counts
   Database	Database where the key is located.

Querying Hot Keys

1. Log in to the management console, and choose Application > Distributed Cache Service in the service list.
2. Click in the upper left corner of the management console and select the region where your instance is located.
3. In the navigation pane, choose Cache Manager.
4. Click the name of a DCS Redis instance.
5. Choose Analysis and Diagnosis > Cache Analysis.
6. On the Hot Key Analysis tab page, you can manually start a hot key analysis or schedule a daily automatic analysis.
   

   To perform hot key analysis, set this parameter to allkeys-lfu or volatile-lfu on the Instance Configuration > Parameters page. For details about allkeys-lfu and volatile-lfu, see What Is the Default Data Eviction Policy?

7. After an analysis task completes, click View to view the analysis results.

   You can also click Download or Delete in the Operation column to download or delete the analysis result.

   

   The hot key analysis result shows the most 100 frequently accessed keys within the specified period.

   Figure 3 Viewing the results of hot key analysis
   

   Table 2 Results of hot key analysis

   Parameter	Description
   Key	The key name in a hot key analysis result.
   Type	Type of a key, which can be string, hash, list, set, or zset.
   Size	The value size of a key, in Bytes.
   FREQ	Reflects the access frequency of a key within a specific period of time (usually 1 minute). FREQ is the logarithmic access frequency counter. The maximum value of FREQ is 255, which indicates 1 million access requests. After FREQ reaches 255, it will no longer increment even if access requests continue to increase. FREQ will decrement by 1 for every minute during which the key is not accessed.
   Shard	Shard where the key is located. NOTE: This parameter is displayed only for cluster instances.
   Database	Database where a key is located.

FAQs About Big Keys and Hot Keys

• Why Is the Capacity or Performance of a Shard of a Redis Cluster Instance Overloaded When That of the Instance Is Still Below the Bottleneck?
• What Is the Impact of a Hot Key?
• How Do I Avoid Big Keys and Hot Keys?
• How Do I Detect Big Keys and Hot Keys in Advance?