Lately i have seen high time to first byte for my sites.
Most of the time it is by javascript. A test at webpagetest.org usually shows like....
URL: http://example.com/
Loaded by: http://example.com/some-kind-of-javascript.js
When i remove that javascript then anothe javascript appears in that place.
What does loaded by exactly mean??
Check example test result....
https://www.webpagetest.org/result/190729_JY_cb028989b0f44671fba830c9eaca29d7/1/details/#waterfall_view_step1
I'm not sure why you think it's Javascript that is the problem? It looks to me like it's the initial HTML that is causing the problem.
Time to First byte for a resource is the time take from after sending the request (e.g. GET /) until it receives the first byte back. It excludes the DNS lookup, TCP connection and SSL handshake time, so really is a measure of the time take to start receiving that resource. Note that the "first byte" time at the top of the waterfall is the full end to end time, including DNS/TCP/SSL and any redirects, but the TTFB for each resource this is split out more.
I don't know how your home page is created - I would guess it's not a static page so whatever is generating this (PHP?) is taking too long. Whether this is due to bad backend code, an under-resourced server, a slow database, or something else is impossible to say from the outside. I would suggest getting in touch with your hosting provider and/or reviewing your code and server.
Related
I need to measure the response time for a file export using Trueclient protocol in loadrunner.After i click on the export button the file will get downloaded. But i am not able to measure the time for the download accurately.
Pull that data from the HTTP request log, which will show the download request, and, if the w3c time-taken value is included in the log, the time required to fulfill the download.
You can process the log at the end of the test for the response time data. If you need to, you cam import a set of datapoints into analysis for representation with the rest of your data. You might want to consider a normalized value for your download, instead of a raw response time. I imagine that the files are of different sizes, so naturally they will have different download times. However, if you divide download bytes with time (in seconds), then you will have a normalized measurement of bytes per second which then allows you to compare one download to the next for consistent operation.
Also, keep in mind that since you are downloading a file, writing to a local disk, for (presumably) multiple users on a host, you will face the risk of turning your local file system into a bottleneck. You can see this same effect if you turn up logging on all users to the highest level and run your test. The wait for lock and wait for write, plus the actual writing of data, becomes a drag anchor to the performance of your virtual user. This is why the recommended log level is "log on error" or send the error to the output window of the controller via lr_output_message() or lr_vuser_status_message(). Consider a control load generator of the same hardware definition as the others with only a single virtual user of this type on it. If the control group and global group degrade together then you have an app issue. If your control user does not degrade, but your other users do, then you have a test bed induced influence on your results.
These are all issues independent of the tool you are using for the test.
I get this every time I try to create an account to ask this on Stack Overflow:
Oops! Something Bad Happened!
We apologize for any inconvenience, but an unexpected error occurred while you were browsing our site.
It’s not you, it’s us. This is our fault.
That's the reason I post it here. I literally cannot ask it on Overflow, even after spending hours of my day (on and off) repeating my attempts and solving a million reCAPTCHA puzzles. Can you maybe fix this error soon?
With no meaningful/complete examples, and basically no documentation whatsoever, I've been trying to use the "shmop" part of PHP for many years. Now I must find a way to send data between two different CLI PHP scripts running on the same machine, without abusing the database for this. It must work without database support, which means I'm trying to use shmop, but it doesn't work at all:
$shmopid = shmop_open(1, 'w', 0644, 99999); // I have no idea what the "key" is supposed to be. It says: "System's id for the shared memory block. Can be passed as a decimal or hex.", so I've given it a 1 and also tried with 123. It gave an error when I set the size to 64, so I increased it to 99999. That's when the error changed to the one I now face above.
shmop_write($shmopid, 'meow 123', 0); // Write "meow 123" to the shared variable.
while (1)
{
$shared_string = shmop_read($shmopid, 0, 8); // Read the "meow 123", even though it's the same script right now (since this is an example and minimal test).
var_dump($shared_string);
sleep(1);
}
I get the error for the first line:
shmop_open(): unable to attach or create shared memory segment 'No error':
What does that mean? What am I doing wrong? Why is the manual so insanely cryptic for this? Why isn't this just a built-in "superarray" that can be accessed across the scripts?
About CLI:
It cannot work in standalone CLI processes, as an answer here says:
https://stackoverflow.com/a/34533749
The master process is the one to hold the shared memory block, so you will have to use php-fpm or mod_php or some other web/service-running version, and maybe even start/request/stop it all from a CLI php script.
About shmop usage itself:
Use "c" mode in shmop_open() for creating the segment before it can be used with "a" or "w".
I stumbled on this error in a different scenario where shared memory is completely optional to speed up some repeated operations. So I wanted to try reading first without knowing memory size and then allocate from actual data when needed. In my case I had to call it as #shmop_open() to hide this error output.
About shmop on Windows:
PHP 7 crashed Apache worker process causing its restart with status 3221225477 when trying to reallocate a segment with the same predefined (arbitrary number) key but different size, even after shmop_delete(). As a workaround for this, I took filemtime() of the source file which contains data to be stored in memory, and used that timestamp as the key in shmop_open(). It still was not flawless IIRC, and I don't know if it would cause memory leaks, but it was enough to test my code which would mainly run on Linux anyway.
Finally, as of PHP version 8.0.7, shmop seems to work fine with Apache 2.4.46 and mod_php in Windows 10.
I am working on a python 3.6 based script to monitor dns resolution time, using dns python. I need to understand what is the best approach to get the resolution time. I am currently using the following:
Method:1
import dns.resolver
import time
dns_start = time.perf_counter()
answers = dns.resolver.query(domain, qtype)
dns_end = time.perf_counter()
print("DNS record is: " ,answers.rrset)
print('DNS time =' ,(dns_end - dns_start)* 1000,"ms")
Method 2
import dns.resolver
import time
answers = dns.resolver.query(domain, qtype)
print("DNS record is: " ,answers.rrset)
print('DNS time =' , answers.response.time * 1000,"ms")
Thanks
"It depends" as the famous saying says.
You need to define what is "best" for you in "best approach". The two methods do things correctly, just different things.
First one will count both network time, remote server processing, and then local generation and parsing of DNS messages, including time spent by Python in the dnspython library.
The second method takes only into account the network and remote processing time: if you search for response_time in https://github.com/rthalley/dnspython/blob/master/dns/query.py you will see it is computed as a difference between the time just before sending the message (hence after it is been build, so the generation time will not be included) and just after it has been received (hence before it is parsed, so parsing time will not be included).
Second method can basically test the remote server performances, irrespective of your local program (including Python itself and the dnspython library) performances (but the network time needed between you and remote server will be counted in).
First method shows the perceived time, as it includes all time needed in the code to do something, that is build the DNS packet and parse the result, actions without which the calling application could do nothing with the DNS content.
I have an EC2 server running Elasticsearch 0.9 with a nginx server for read/write access. My index has about 750k small-medium documents. I have a pretty continuous stream of minimal writes (mainly updates) to the content. The speeds/consistency I receive with search is fine with me, but I have some sporadic timeout issues with multi-get (/_mget).
On some pages in my app, our server will request a multi-get of a dozen to a few thousand documents (this usually takes less than 1-2 seconds). The requests that fail, fail with a 30,000 millisecond timeout from the nginx server. I am assuming this happens because the index was temporarily locked for writing/optimizing purposes. Does anyone have any ideas on what I can do here?
A temporary solution would be to lower the timeout and return a user friendly message saying documents couldn't be retrieved (however they still would have to wait ~10 seconds to see an error message).
Some of my other thoughts were to give read priority over writes. Anytime someone is trying to read a part of the index, don't allow any writes/locks to that section. I don't think this would be scalable and it may not even be possible?
Finally, I was thinking I could have a read-only alias and a write-only alias. I can figure out how to set this up through the documentation, but I am not sure if it will actually work like I expect it to (and I'm not sure how I can reliably test it in a local environment). If I set up aliases like this, would the read-only alias still have moments where the index was locked due to information being written through the write-only alias?
I'm sure someone else has come across this before, what is the typical solution to make sure a user can always read data from the index with a higher priority over writes. I would consider increasing our server power, if required. Currently we have 2 m2x-large EC2 instances. One is the primary and the replica, each with 4 shards.
An example dump of cURL info from a failed request (with an error of Operation timed out after 30000 milliseconds with 0 bytes received):
{
"url":"127.0.0.1:9200\/_mget",
"content_type":null,
"http_code":100,
"header_size":25,
"request_size":221,
"filetime":-1,
"ssl_verify_result":0,
"redirect_count":0,
"total_time":30.391506,
"namelookup_time":7.5e-5,
"connect_time":0.0593,
"pretransfer_time":0.059303,
"size_upload":167002,
"size_download":0,
"speed_download":0,
"speed_upload":5495,
"download_content_length":-1,
"upload_content_length":167002,
"starttransfer_time":0.119166,
"redirect_time":0,
"certinfo":[
],
"primary_ip":"127.0.0.1",
"redirect_url":""
}
After more monitoring using the Paramedic plugin, I noticed that I would get timeouts when my CPU would hit ~80-98% (no obvious spikes in indexing/searching traffic). I finally stumbled across a helpful thread on the Elasticsearch forum. It seems this happens when the index is doing a refresh and large merges are occurring.
Merges can be throttled at a cluster or index level and I've updated them from the indicies.store.throttle.max_bytes_per_sec from the default 20mb to 5mb. This can be done during runtime with the cluster update settings API.
PUT /_cluster/settings HTTP/1.1
Host: 127.0.0.1:9200
{
"persistent" : {
"indices.store.throttle.max_bytes_per_sec" : "5mb"
}
}
So far Parmedic is showing a decrease in CPU usage. From an average of ~5-25% down to an average of ~1-5%. Hopefully this can help me avoid the 90%+ spikes I was having lock up my queries before, I'll report back by selecting this answer if I don't have any more problems.
As a side note, I guess I could have opted for more balanced EC2 instances (rather than memory-optimized). I think I'm happy with my current choice, but my next purchase will also take more CPU into account.
Ive found this gem : http://watirwebdriver.com/page-performance/
But i cant seem to understand what this measures
browser.performance.summary[:response_time]/1000
Does it start measuring from the second i open the browser?
Watir::Browser.new :chrome
or from the last Watir-webdriver command writen?
And how can i set when it starts the timer?
** I've tried several scripts but i keep getting 0 seconds
Thats why im not sure.**
From what I have read (I have not actually used it on a project), the response_time is the time from starting navigation to the end of the page loading - see Tim's (the gem's author) answer in a previous question. The graphical image on Tim's blog will helps to understand the different values - http://90kts.com/2011/04/19/watir-webdriver-performance-gem-released/.
The gem is for getting performance results of single response, rather than overall usage of a browser during a script. So there is no need to start/stop the timer.
If you are getting 0 seconds, it likely means that the response_time is less than 1000 milliseconds (ie in Ruby, doing 999/1000 gives 0). To make sure you are getting something non-zero, try doing:
browser.performance.summary[:response_time]/1000.0
Dividing by 1000.0 will ensure that you get the decimal values (eg 0.013).