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Nginxdevops~10 mins

Open file cache in Nginx - Step-by-Step Execution

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Process Flow - Open file cache
Request for file
Check open file cache
Serve file
Return response
Serve file
Return response
When nginx receives a file request, it first checks the open file cache. If the file is cached (hit), it serves it directly. If not (miss), it opens the file from disk, adds it to the cache, then serves it.
Execution Sample
Nginx
open_file_cache max=1000 inactive=20s;
open_file_cache_valid 30s;
open_file_cache_min_uses 2;

location /images/ {
}
This config sets up nginx to cache open files with limits and validity times, improving file serving performance.
Process Table
StepActionCache StateFile OpenedResponse
1Request file /images/logo.pngEmptyNoNo response yet
2Check cache for /images/logo.pngEmptyNoCache miss
3Open /images/logo.png from diskEmptyYesNo response yet
4Add /images/logo.png to cacheContains /images/logo.pngYesNo response yet
5Serve /images/logo.png from cacheContains /images/logo.pngYesFile content sent
6Request file /images/logo.png againContains /images/logo.pngNoNo response yet
7Check cache for /images/logo.pngContains /images/logo.pngNoCache hit
8Serve /images/logo.png from cacheContains /images/logo.pngNoFile content sent
9Request file /images/banner.pngContains /images/logo.pngNoNo response yet
10Check cache for /images/banner.pngContains /images/logo.pngNoCache miss
11Open /images/banner.png from diskContains /images/logo.pngYesNo response yet
12Add /images/banner.png to cacheContains /images/logo.png, /images/banner.pngYesNo response yet
13Serve /images/banner.png from cacheContains /images/logo.png, /images/banner.pngYesFile content sent
14Cache entry /images/logo.png inactive for 21sContains /images/logo.png, /images/banner.pngYesNo response yet
15Remove /images/logo.png from cache due to inactivityContains /images/banner.pngNoNo response yet
16Request file /images/logo.pngContains /images/banner.pngNoNo response yet
17Check cache for /images/logo.pngContains /images/banner.pngNoCache miss
18Open /images/logo.png from diskContains /images/banner.pngYesNo response yet
19Add /images/logo.png to cacheContains /images/banner.png, /images/logo.pngYesNo response yet
20Serve /images/logo.png from cacheContains /images/banner.png, /images/logo.pngYesFile content sent
💡 Execution stops after serving files and cache updates; cache entries removed after inactivity timeout.
Status Tracker
VariableStartAfter Step 4After Step 8After Step 12After Step 15After Step 20
open_file_cacheempty/images/logo.png/images/logo.png/images/logo.png, /images/banner.png/images/banner.png/images/banner.png, /images/logo.png
file_openedNoYesNoYesNoYes
response_sentNoNoYesNoNoYes
Key Moments - 3 Insights
Why does nginx open the file from disk even though it was requested before?
Because the file was removed from the cache after being inactive for longer than the inactive timeout (step 15), so nginx must open it again (step 18).
What happens when a file is requested and found in the open file cache?
Nginx serves the file directly from the cache without opening it again on disk, as shown in steps 6-8.
How does nginx decide to remove a file from the open file cache?
If a cached file is inactive longer than the configured inactive time (20s here), nginx removes it from the cache (step 15).
Visual Quiz - 3 Questions
Test your understanding
Look at the execution table, at which step does nginx add /images/banner.png to the cache?
AStep 10
BStep 12
CStep 14
DStep 16
💡 Hint
Check the 'Action' column for 'Add /images/banner.png to cache' in the execution table.
According to the variable tracker, what is the state of open_file_cache after step 15?
AContains /images/logo.png and /images/banner.png
BEmpty
CContains /images/banner.png only
DContains /images/logo.png only
💡 Hint
Look at the 'open_file_cache' row under 'After Step 15' in the variable tracker.
If the inactive time was set to 60s instead of 20s, what would change in the execution table?
AStep 15 (removal of /images/logo.png) would not occur
BCache misses would increase
CFiles would never be added to cache
DFiles would be opened from disk every time
💡 Hint
Consider the cache removal step based on inactivity timeout in the execution table.
Concept Snapshot
open_file_cache caches open file descriptors to speed up file serving.
Configure max entries, inactive timeout, and validity.
Cache hit serves file directly; miss opens file and caches it.
Inactive files removed after timeout to save resources.
Improves performance by reducing disk opens.
Full Transcript
This visual execution shows how nginx handles open file caching. When a file is requested, nginx checks if it is in the open file cache. If found (cache hit), nginx serves it directly without opening the file again on disk. If not found (cache miss), nginx opens the file from disk, adds it to the cache, then serves it. Cached files are removed after being inactive longer than the configured inactive timeout. The execution table traces requests, cache hits and misses, file openings, and cache updates step-by-step. The variable tracker shows how the cache contents and file open states change over time. Key moments clarify why files are reopened after removal and how cache hits speed up serving. The quiz tests understanding of cache addition, removal, and configuration effects. This helps beginners see exactly how open file caching works in nginx to improve performance.