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Tencent Cloud Distributed Cache (Redis OSS-Compatible)

Monitoring Overview

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Last updated: 2026-09-08 15:48:31
AI-Translated
Distributed Cache provides a complete monitoring data collection system that covers three dimensions: Proxy nodes, Redis nodes, and instances. The monitoring system collects performance metrics from each node in real time at second-level granularity and presents accurate, comprehensive monitoring views after unified aggregation. This section describes the complete processing flow of monitoring data from collection to display, helping you better understand the meaning and characteristics of monitoring metrics.

Proxy Node Data Collection

Each Distributed Cache instance contains at least 3 Proxy nodes (typically 1.5 times the number of Redis nodes). Proxy nodes serve as the access proxy layer between clients and Redis nodes, collecting monitoring data in real time across the following dimensions:
Collection Dimension
Collection methods
Representative Metric
CPU resources
Collect the CPU utilization of Proxy processes in real time.
cpu_util
Request statistics
Collect command execution counts and type distribution through Proxy.
proxy_commands,cmd_key_count,cmd_mget,cmd_err,cmd_big_value
Network traffic
Collect inbound and outbound network traffic and bandwidth utilization.
in_flow,out_flow,in_bandwidth_util,out_bandwidth_util
Traffic throttling
Record the number of times bandwidth throttling is triggered.
in_flow_limit,out_flow_limit
Connection management
Collect the number and utilization of client TCP connections.
connections,connections_util,connections_max_util
Execution latency
Collect command execution latency distribution between Proxy and Redis Server.
latency_avg,latency_max,latency_read,latency_write,latency_other
Note:
The latency metric of Proxy nodes reflects the time elapsed from when the Proxy receives a client command to when it receives a response from the Redis Server, accurately indicating the internal processing efficiency of the database.

Data Node Data Collection

Data node monitoring covers all master nodes and replica nodes within an instance. Data node metrics are collected in the following ways based on their characteristics:
Collection methods
Description
Representative Metric
Real-time status collection
Directly read the status information of the data node at runtime to obtain the instantaneous value at the current moment.
cpu_util (CPU utilization), connections (number of connections), mem_used (memory usage), mem_util (memory utilization), keys (total number of keys), expires (number of keys with expiration time set)
Periodic increment calculation
In each collection cycle, calculate the change in the metric value relative to the previous cycle, reflecting the incremental change within the collection cycle.
expired (number of expired keys), evicted (number of evicted keys), cmd_slow (number of slow queries), cmd_hits (number of read request hits), cmd_miss (number of read request misses)
Rate calculation
Divide the result of the incremental calculation by the collection interval to obtain the per-second rate, reflecting the processing capability per unit time.
commands (total request QPS), cmd_read (read request QPS), cmd_write (write request QPS), cmd_other (other request QPS)
Combined derivative calculation
Generate derived metrics based on combined calculations of multiple basic metrics, reflecting higher-level performance characteristics.
cmd_hits_ratio (read request hit ratio = hits / (hits + misses))
Note:
For metrics based on periodic incremental calculation and rate calculation, the monitoring system requires data from multiple consecutive collection cycles to output stable metric values. Shortly after an instance starts or a failover occurs, these metrics may experience brief data fluctuations, which is normal.

Instance-Level Data Aggregation

Instance-level monitoring data is not collected independently. Instead, it is aggregated from Proxy node and Redis node monitoring data through aggregation algorithms. Different monitoring metrics use different aggregation methods based on their business meanings:
Aggregation Algorithm
Scenarios
Representative Metric
Calculation Method
SUM
Countable metrics that can be summed, where the combined values of all nodes represent the total instance count.
commands (total request QPS), cmd_read (read request QPS), cmd_write (write request QPS), cmd_slow (slow query count), cmd_hits (hit count), cmd_miss (miss count)
Sum the metric values of all nodes involved in aggregation.
AVG
Ratio metrics that need to reflect the overall average level of an instance
cpu_util (CPU utilization)
Calculate the arithmetic mean of metric values across all Redis nodes, including master and replica nodes.
MAX (maximum value)
Metrics that need to reflect the bottleneck node status within an instance
cpu_max_util (maximum node CPU utilization), mem_max_util (maximum node memory utilization), connections_max_util (maximum node connection utilization)
Take the maximum metric value among all nodes involved in aggregation.
Weighted average
Ratio metrics whose global characteristics cannot be accurately reflected by simple averaging need to be weighted based on the actual data volume of each node.
cmd_hits_ratio (read request hit ratio)
Total hits of all nodes / (total hits of all nodes + total misses of all nodes), rather than the simple average of the hit ratio of each node.
LAST (latest value)
Take the value from the latest collection.
Some status metrics
Take the value from the most recent collection cycle.
Note:
The read request hit ratio (cmd_hits_ratio) is calculated using a weighted average algorithm, which more accurately reflects the overall cache hit status of the instance compared with a simple average. For example, when access volumes vary significantly across nodes, a simple average may be skewed by low-traffic nodes, whereas a weighted average is calculated based on the actual total number of hits and misses, producing more accurate data. When the instance has no access requests, this value is null.

Skewness Metric

The skew ratio metric is used to evaluate the CLB degree among shards in a cluster architecture instance. It is calculated as the ratio of a single node's metric value to the average value of all nodes participating in aggregation within the instance. When the skew ratio is greater than 100%, it indicates that the node's load is higher than the average level and that skew exists.
Note:
When a skew ratio metric remains above 150%, you are advised to check the load of the corresponding shard and improve CLB through capacity expansion or data distribution optimization if necessary.
Metric
Metric Name
Description
Total request tilt rate
qps_slope_util
Reflects the balance of request volume across shards.
Memory utilization tilt rate
mem_util_slope_util
Reflects the balance of memory usage across shards.

Special Scenarios for Monitoring Data

In the following scenarios, monitoring data may experience brief fluctuations or changes, which is normal:
Scenario
Impact
Description
Instance initialization
Brief fluctuations in some metrics
Incremental calculation metrics (such as QPS and slow query quantity) require data from consecutive collection cycles to output stable values, and may briefly show zero or abnormal values during the initial startup phase.
Primary-secondary switch
Brief data interruption
During a failover, there may be a brief data gap between when the original node stops reporting and when the new node starts reporting. After the switchover is complete, monitoring data is automatically restored.
Scale-out or scale-in
Node ID change
Scale-out and scale-in operations cause node ID changes. If you query monitoring data by node through the API, you need to obtain node information again after the operation is complete. For details, see DescribeInstanceNodeInfo.
Enabling or disabling read-only replica
Instance-level metric baseline change
After enabling or disabling the read-only replica feature, the scope of nodes involved in instance-level aggregate calculation may change, and the value baselines of some metrics may be adjusted accordingly.

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