> - a cache hit means that the resource should also be in the linux
page cache - so no physical disk read needed.
That's a very wrong assumption to make, and only makes sense in very
small scale setups - and multiple terabytes of memory isn't exactly
cheap, that's why we have SSD storage to handle such things, and it
would still be a "HIT" even if it's not within the memory.
Peter Booth wrote:
This might not be a bug at all. Remember that when nginx logs request
time it's doing so with millisecond precision. This is very, very
coarse-grained when you consider what
modern hardware is capable of. The Tech Empower benchmarks shwo that
an (openresty) nginx on
a quad-socket host can server more than 800,000 dynamic lua requests
per second. We should expect
that static resources served from ngixn cache to be faster than this.
Remember:
- a cache hit means that the resource should also be in the linux
page cache - so no physical disk read needed.
- writing a small png file from memory to the network (on a 10G
ethernet ) could take a few microsec. Depending on NIC IRQ
consolidation settings this might be as much as 60/70micros.
- reading the time (gettimeofday()) will itself take about 30 nanoseconds.
These are al intervals that are too small to be visible to the 1ms
granularity of the request_time logging.
My experience has been that very busy webservers running on even five
year old hardware
will consistently log 0ms request time for cache hits. If I saw
anything different I'd be wondering
what was wrong with the environment.
Peter
On Jun 22, 2017, at 05:53 AM, jindov <nginx-fo...@forum.nginx.org> wrote:
Hi guys,
I've configured for nginx to cache static like jpeg|png. The problem
is if
request with MISS status, it will show a non-zero value request_time,
but if
a HIT request, the request_time value is 0.000.
This is an nginx bug and is there anyway to resolve it.
My log format
```
log_format cache '$remote_addr - [$time_local] $upstream_cache_status
$upstream_addr '
'"$request" $status $body_bytes_sent $request_time
["$upstream_response_time"] "$http_referer" '
'"$http_user_agent" "$host" "$server_port"
"$connection"';
```
I read a topic about this but this is not informational. I've try to set
timer_resolution to 0ms but nothing was changed
Thanks
Posted at Nginx Forum:
https://forum.nginx.org/read.php?2,275053,275053#msg-275053
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