inconsistency between docker stats command and docker rest api memory stats - docker

Question

when looking at a running container with docker stats command, I can see that the memory usage of a container is 202.3MiB.
However, when looking at the same container through the REST API with
GET /containers/container_name/stats -> memory_stats-> usage , the usage there shows 242.10 MiB.
there is a big difference between those values.
What might be the reason for the difference? I know that the docker client uses the REST API to get its stats, but what am I missing here?

Answer 1

Solved my problem. Initially, I did not take into account cache memory when calculating memory usage.
Say "stats" is the returned json from
GET /containers/container_name/stats,
the correct formula is:
memory_usage = stats["memory_stats"]["usage"] - stats["memory_stats"]["stats"]["cache"]
limit = stats["memory_stats"]["limit"]
memory_utilization = memory_usage/limit * 100

Answer 2

Use the rss value i.e (rss = usage - cache)
"memory_stats": {
"stats": {
"cache": 477356032,
"rss": 345579520,
},
"usage": 822935552
}
On Linux, the Docker CLI reports memory usage by subtracting page cache usage from the total memory usage.
The API does not perform such a calculation but rather provides the total memory usage and the amount from the page cache so that clients can use the data as needed. (https://docs.docker.com/engine/reference/commandline/stats/)

Answer 3

The accepted answer is incorrect for recent Docker versions (version greater than 19.03).
The correct way that gets the same number docker stats reports is:
memory = stats['memory_stats']['usage'] - stats["memory_stats"]["stats"]["total_inactive_file"]
memory_limit = stats['memory_stats']['limit']
memory_perc = (memory / memory_limit) * 100

Answer 4

JavaScript code according to the Docker cli source code:
const memStats = stats.memory_stats
const memoryUsage = memStats.stats.total_inactive_file && memStats.stats.total_inactive_file < memStats.usage
? memStats.usage - memStats.stats.total_inactive_file
: memStats.usage - memStats.stats.inactive_file