Our setup is as follows:
Primary DB Server, Amazon EC2 m2.xlarge instance (17GB ram, 2x3.25ecu CPU) running Percona 5.5.x
Application Server(s), Amazon EC2 m1.large instance (7.5GB ram, 2x2ecu CPU) running PHP 5.4
php-handlersocket PECL library found here http://code.google.com/p/php-handlersocket/
For the most part it works but as soon as I load up the app server with even relative traffic, the results start failing on queries where the result record(s) have fields with medium to large values. The two main culprits in our case are XML strings that are ~5Kb, and media files stored as binary objects 5-500Kb. The symptom is if I request 10 fields and the XML is in the 8th field, I'll get 7 results with data, and the 8th will be empty, 9 and 10 are not included at all.
There is a reported issue for the php-handlersocket library relating to this kind of problem, however there's also a proposed fix, which I've implemented and I thought it helped, but it seems not entirely. The issue details and fix are here http://code.google.com/p/php-handlersocket/issues/detail?id=28
My HandlerSocket settings are just slightly different than the defaults, should I be setting these different?
loose_handlersocket_port = 9998
loose_handlersocket_port_wr = 9999
loose_handlersocket_threads = 4
loose_handlersocket_threads_wr = 1
open_files_limit = 65535
I've reduced the default read threads to 4 since they recommend CORES * 2, the default is 16. I thought slower responses would be better than none at all, but this didn't seem to make a difference.
The php-handlersocket project looks to be dead which on it's own is a bit surprising, the last source updates were more than a year ago, but there doesn't seem to be any other PHP library available so I'm stuck.
I'm wondering if anyone has had similar problems, if there are other libraries available or if I should be exploring skipping libraries and creating my own interface with something like CURL.
So in the end, as with many problems, I became wary of an open source project with limited attention and decided to write my own php sockets based solution that's working perfectly.
Related
TL;DR – What's the simplest approach to very quickly loading large files (~tens of MB) in PHP to avoid responsiveness issues in a web page? For example, I suspect I'll need to do something like pre-loading the files and sharing the resulting large (static) associative arrays from one PHP instance to the instances created by the web server. I'm specifically trying to avoid having to deal with SQL...
Details
I've put together an online dictionary (here) with a home-brew search engine that works beautifully on my local computer, but has performance problems on the server. (Note: I have no control over the server aside from updating my own files.)
The performance problems are largely due to the index files that I need to load (large associative arrays, json encoded). These are on the order of 6-16 MB and only those required for the specific type of search are loaded. This means non-typical searches (e.g., searching specifically in quotes or etymology) show a significant performance hit due to the necessity of loading extra (large) files.
Now, I realize many people will tell me that I should be using SQL or some other DB solution instead of loading and searching my own index files. They're correct, but right now I don't have the time or energy to fight with learning how to roll my own SQL server, converting all my data structures over to SQL format, and figuring out how to interface PHP with SQL, etc. I have no experience with SQL and all the tutorials I've looked at so far make it seem ill suited to my data structures (i.e., I can't define my records in terms of fixed-width strings because I have arbitrary length blocks of text for every entry and arbitrary numbers of entries associated with a given headword, etc.)
Again, my current code works perfectly on my local computer - all the problems boil down to the time expensive step of loading these large index files. A "simple" fix (that allows me to keep my current design) would seem to be pre-loading these index files in a separate script and then have any PHP instances created by the web server access these static data structures that already exist in memory (again, they're just a bunch of large/complex associative arrays). These data structures/files are static, so locking/race conditions aren't an issue (i.e., the data only changes periodically when I push out updates with corrections/updated inflection lists, etc.).
I've attempted to find information on how to approach this, but the results are confusing and contradictory and are beyond the scope of things I've worked with before. I'm happy to learn new things, but it's not clear which path will even work for what I'm trying to do.
Lot's of (older?) recommendations to use ACP, but I see comments that this only works for instances on the same processor - so even if they're on the same server it may not work (even worse, maybe the host server will spread different instances across different virtual machines). I also see comments that some aspects of ACP are deprecated as well as discussions about re-compiling PHP with various flags - this is obviously not an option for me; I only have what's available on the server.
A recommendation to use built in IPC functions within PHP (link) - but it's not clear if I can carve out a ~50 MB chunk to share (the way it's written makes it sound like this is for small chunks of memory) and some of the comments suggest there can memory collision problems or that this would cause performance issues and a daemon/socket approach (see comments at the end of the linked article). Honestly, this approach looks appealing as I can just use my existing data structures. However, I'm worried this will have the same problems as those leveled at APC (e.g., will this work if the server is putting different instances on different virtual machines?)
Daemon/socket approach - a comment in the link above claims this would be best performance-wise. I haven't worked with sockets before, but I feel like it would be less painful to learn this than restructuring everything around an SQL approach (maybe that's a bad assessment on my part?) I can at least conceptualize how this would work, but I would need to learn how to get a daemon script that's always running in the background and ensure it's responsive to multiple simultaneous instances, etc.
I'm sure there are other approaches that I haven't yet stumbled across.
Again, ideally, I'd like an approach that simply lets me load all the index files and hang those associative arrays out in the wind for everyone to look at. Security's not an issue (it's just a processed version of the data in the simple web pages) and the data is static.
Note: the web server is running PHP 7.4 (Zend 3.4) and my local environment is OSX 10.14 or 10.15 with PHP 7.3 (Zend 3.3)
The easiest solution is to use memcached to store your large objects. It is well supported in PHP. You will need to increase the maximum object size, the default is 1MB, but this is a simple configuration option.
Got an obscure one. Been at this one for weeks. Here is what we’re doing:
Upgrade of Silverstripe 3.1 -> 3.7
Upgrade of Platform. PHP 5.6 -> 7.4, Postgres 9.5 -> 13
Old system is running mod_php, New is running PHP_FPM
Parallel hosting systems running. Old and New. Both have identical resources.
Performance tests run on both systems for Old -> New comparisons.
Both platforms consist of two App nodes, and one DB node
Most tests are great. PHP 7.4 obviously smokes the old system. But one test is Apache Bench just hitting home page. Which shows a pretty serious degradation on the New system. Digging further into this, we created a series of test files for Apache Bench to hit that isolate specific things - Static HTML, Raw PHP, PHP + Raw pg_ commands and queries.
All thrash the old system except the latter. DB interactions. So drilling down further we created a new target file that simply does a pg_connect() and immediately closes it, then hit that with Apache Bench. Same result as the query test script. Suggesting the deficit is in the action of pg_connect(). Database connections.
Clearly there's a lot of variables in this issue. And I'm loath to pack this question out with a bunch of details about the tests (and other tests like pgbench) until needed. I'm more hoping to stumble across someone who has observed a similar issue with pg_connect() specifically, and has even the most random idea for an angle to test.
Other testing ideas would be welcome. One thing we are trying to work out right now is how to get connection timing from pgbench to see if the issue exists on Postgres itself. Our tests are as follows:
Apache Bench hitting several target pages
PGBench (showing the new system performing better than the old)
PHP test
jMeter is being set up now
UPDATE
We've done a bit of manual digging in the Postgres logs in each environment, and see something a bit strange looking at the received/authorised log entry pairs like this:
2021-05-19 11:34:25.708 NZST,,,404734,"10.220.218.21:50560",60a44f01.62cfe,1,"",2021-05-19 11:34:25 NZST,,0,LOG,00000,"connection received: host=xx.xx.xx.xx port=50560",,,,,,,,,""
2021-05-19 11:34:25.908 NZST,"db_user","db_name",404734,"xx.xx.xx.xx:50560",60a44f01.62cfe,2,"authentication",2021-05-19 11:34:25 NZST,7/486524,0,LOG,00000,"connection authorized: user=db_user database=db_name",,,,,,,,,""
I captured a bunch of these pairs on both environments (Old and New) and calculated the gap between the recieved log message and the authentication log message.
On Old, the average is 0.011s. On New, the average is 0.195s. Difference aside, this makes no sense, as the test page on the application node of that environment takes ~0.02s to complete in full.
We try to deploy APC user-cache in a high load environment as local 2nd-tier cache on each server for our central caching service (redis), for caching database queries with rarely changing results, and configuration. We basically looked at what Facebook did (years ago):
http://www.slideshare.net/guoqing75/4069180-caching-performance-lessons-from-facebook
http://www.slideshare.net/shire/php-tek-2007-apc-facebook
It works pretty well for some time, but after some hours under high load, APC runs into problems, so the whole mod_php does not execute any PHP anymore.
Even a simple PHP script with only does not answer anymore, while static resources are still delivered by Apache. It does not really crash, there is no segfault. We tried the latest stable and latest beta of APC, we tried pthreads, spin locks, every time the same problem. We provided APC with far more memory it can ever consume, 1 minute before a crash we have 2% fragmentation and about 90% of the memory is free. When it „crashes“ we don’t find nothing in error logs, only restarting Apache helps. Only with spin locks we get an php error which is:
PHP Fatal error: Unknown: Stuck spinlock (0x7fcbae9fe068) detected in
Unknown on line 0
This seems to be a kind of timeout, which does not occur with pthreads, because those don’t use timeouts.
What’s happening is probably something like that:
http://notmysock.org/blog/php/user-cache-timebomb.html
Some numbers: A server has about 400 APC user-cache hits per second and about 30 inserts per second (which is a lot I think), one request has about 20-100 user-cache requests. There are about 300.000 variables in the user-cache, all with ttl (we store without ttl only in our central redis).
Our APC-settings are:
apc.shm_segments=1
apc.shm_size=4096M
apc.num_files_hint=1000
apc.user_entries_hint=500000
apc.max_file_size=2M
apc.stat=0
Currently we are using version 3.1.13-beta compiled with spin locks, used with an old PHP 5.2.6 (it’s a legacy app, I’ve heard that this PHP version could be a problem too?), Linux 64bit.
It's really hard to debug, we have written monitoring scripts which collect as much data as we could get every minute from apc, system etc., but we cannot see anything uncommon - even 1 minute before a crash.
I’ve seen a lot of similar problems here, but by now we couldn’t find a solution which solves our problem yet. And when I read something like that:
http://webadvent.org/2010/share-and-enjoy-by-gopal-vijayaraghavan
I’m not sure if going with APC for a local user-cache is the best idea in high load environments. We already worked with memcached here, but APC is a lot faster. But how to get it stable?
best regards,
Andreas
Lesson 1: https://www.kernel.org/doc/Documentation/spinlocks.txt
The single spin-lock primitives above are by no means the only ones. They
are the most safe ones, and the ones that work under all circumstances,
but partly because they are safe they are also fairly slow. They are slower
than they'd need to be, because they do have to disable interrupts
(which is just a single instruction on a x86, but it's an expensive one -
and on other architectures it can be worse).
That's written by Linus ...
Spin locks are slow; that assertion is not based on some article I read online by facebook, but upon the actual facts of the matter.
It's also, an incidental fact, that spinlocks are deployed at levels higher than the kernel because of the very problems you speak of; untraceable deadlocks because of a bad implementation.
They are used by the kernel efficiently, because that's where they were designed to be used, locking tiny tiny tiny sections, not sitting around and waiting for you to copy your amazon soap responses into apc and back out a billion times a second.
The most suitable kind of locking (for the web, not the kernel) available in APC is definitely rwlocks, you have to enable rwlocks with a configure option in legacy APC and it is the default in APCu.
The best advice that can be given, and I already gave it, is don't use spinlocks, if mutex are causing your stack to deadlock then try rwlocks.
Before I continue, your main problem is you are using a version of PHP from antiquity, which nobody even remembers how to support, in general you should look to upgrade, I'm aware of the constraints on the OP, but it would be irresponsible to negate to mention that this is a real problem, you do not want to deploy on unsupported software. Additionally APC is all but unmaintained, it is destined to die. O+ and APCu are it's replacement in modern versions of PHP.
Anyway, I digress ...
Synchronization is a headache when you are programming at the level of the kernel, with spinlocks, or whatever. When you are several layers removed from the kernel, when you rely on 6 or 7 bits of complicated software underneath you synchronizing properly in order that your code can synchronize properly synchronization becomes, not only a headache for the programmer, but for the executor too; it can easily become the bottleneck of your shiny web application even if there are no bugs in your implementation.
Happily, this is the year 2013, and Yahoo aren't the only people able to implement user caches in PHP :)
http://pecl.php.net/package/yac
This is an, extremely clever, lockless cache for userland PHP, it's marked as experimental, but once you are finished, have a play with it, maybe in another 7 years we won't be thinking about synchronization issues :)
I hope you get to the bottom of it :)
Unless you are on a freebsd derived operating system it is not a good idea to use spinlocks, they are the worst kind of synchronization on the face of the earth. The only reason you must use them in freebsd is because the implementer negated to include PTHREAD_PROCESS_SHARED support for mutex and rwlocks, so you have little choice but to use the pg-sql inspired spin lock in that case.
Running WordPress on IIS 7 (Windows Server 2008) with WP-SuperCache as per IIS.net's guide.
Was running great but recently we changed the permissions on some folders and the administrator password and we're getting huge spikes in our CPU usage as a result of the PHP-cgi.exe processes.
This leads me to believe it's not caching however the pages themselves have the "Cached with WP-SuperCache" comments at the bottom, and the caching seems to be working correctly.
What else could be the issue here?
I think I may have found a solution or at least a work round to this problem, at least it seems to be working for me reliably.
Try setting the Max Instances setting, under IIS Server --> FastCGI Settings, to 1.
It seemed to me that only certain requests were causing a php-cgi.exe process to go rogue and hog the cpu, usually when updating a post. When reading other posts on this issue one of them mentioned the Max Instances setting and that it is set to default at 0 or automatic. I wondered if this might not have a good effect when things aren't as they should be. I'm guessing (but this isn't quite my field of expertise) if a certain request(s) is causing the process to lock-up, so FastCGI just creates another, whilst leaving the first in place. Somehow it seems only having a single instance allows PHP to move on from the lock-up and the cpu stays under control.
For servers with high-levels of requests setting FastCGI to only a single instance may not be ideal, but it certainly beats the delays I was getting before. Used in combination with WP-SuperCache and WinCache, things seem to nipping along nicely now.
Looking at that task mgr looks like its missing the cache on every request. Plus that article dates to 2008 so difficult to say whether the directions as written would still work. Something with WP-SuperCache could have changed.
I would recommend using W3 Total Cache. I've done extensive testing with it on Windows Server 2008 and IIS 7 and it works great. It is also compatible with and leverages the WinCache extension for PHP. Has some other great features too if you're interested, minification, CDN support, etc. It's a really great performance plugin for WordPress. You can get the plugin here, http://wordpress.org/extend/plugins/w3-total-cache/
some other things to check...
What size is the app pool? (# of processes?)
Make sure you are using PHP 5.3.
Make sure you are using WinCache.
Make sure to set MaxInstanceRequests to something less than PHP_FCGI_MAX_REQUESTS. Definitely do not allow PHP to handle recyling the app pool. The default is 10K requests. If you are seeing these results during a load test then this might be the cause. Increase MaxInstanceRequests and keep it one less than PHP_FCGI_MAX_REQUESTS.
Hope that helps.
We run a medium-size site that gets a few hundred thousand pageviews a day. Up until last weekend we ran with a load usually below 0.2 on a virtual machine. The OS is Ubuntu.
When deploying the latest version of our application, we also did an apt-get dist-upgrade before deploying. After we had deployed we noticed that the load on the CPU had spiked dramatically (sometimes reaching 10 and stopping to respond to page requests).
We tried dumping a full minute of Xdebug profiling data from PHP, but looking through it revealed only a few somewhat slow parts, but nothing to explain the huge jump.
We are now pretty sure that nothing in the new version of our website is triggering the problem, but we have no way to be sure. We have rolled back a lot of the changes, but the problem still persists.
When look at processes, we see that single Apache processes use quite a bit of CPU over a longer period of time than strictly necessary. However, when using strace on the affected process, we never see anything but
accept(3,
and it hangs for a while before receiving a new connection, so we can't actually see what is causing the problem.
The stack is PHP 5, Apache 2 (prefork), MySQL 5.1. Most things run through Memcached. We've tried APC and eAccelerator.
So, what should be our next step? Are there any profiling methods we overlooked/don't know about?
The answer ended up being not-Apache related. As mentioned, we were on a virtual machine. Our user sessions are pretty big (think 500kB per active user), so we had a lot of disk IO. The disk was nearly full, meaning that Ubuntu spent a lot of time moving things around (or so we think). There was no easy way to extend the disk (because it was not set up properly for VMWare). This completely killed performance, and Apache and MySQL would occasionally use 100% CPU (for a very short time), and the system would be so slow to update the CPU usage meters that it seemed to be stuck there.
We ended up setting up a new VM (which also gave us the opportunity to thoroughly document everything on the server). On the new VM we allocated plenty of disk space, and moved sessions into memory (using memcached). Our load dropped to 0.2 on off-peak use and around 1 near peak use (on a 2-CPU VM). Moving the sessions into memcached took a lot of disk IO away (we were constantly using about 2MB/s of disk IO, which is very bad).
Conclusion; sometimes you just have to start over... :)
Seeing an accept() call from your Apache process isn't at all unusual - that's the webserver waiting for a new request.
First of all, you want to establish what the parameters of the load are. Something like
vmstat 1
will show you what your system is up to. Look in the 'swap' and 'io' columns. If you see anything other than '0' in the 'si' and 'so' columns, your system is swapping because of a low memory condition. Consider reducing the number of running Apache children, or throwing more RAM in your server.
If RAM isn't an issue, look at the 'cpu' columns. You're interested in the 'us' and 'sy' columns. These show you the percentage of CPU time spent in either user processes or system. A high 'us' number points the finger at Apache or your scripts - or potentially something else on the server.
Running
top
will show you which processes are the most active.
Have you ruled out your database? The most common cause of unexpectedly high load I've seen on production LAMP stacks come down to database queries. You may have deployed new code with an expensive query in it; or got to the point where there are enough rows in your dataset to cause previously cheap queries to become expensive.
During periods of high load, do
echo "show full processlist" | mysql | grep -v Sleep
to see if there are either long-running queries, or huge numbers of the same query operating at once. Other mysql tools will help you optimise these.
You may find it useful to configure and use mod_status for Apache, which will allow you to see what request each Apache child is serving and for how long it has been doing so.
Finally, get some long-term statistical monitoring set up. Something like zabbix is straightforward to configure, and will let you monitor resource usage over time, such that if things get slow, you have historical baselines to compare against, and a better ieda of when problems started.
Perhaps you where using worker MPM before and now you are not?
I know PHP5 does not work with the Worker MPM. On my Ubuntu server, PHP5 can only be installed with the Prefork MPM. It seems that PHP5 module is not compatible with multithreading version of Apache.
I found a link here that will show you how to get better performance with mod_fcgid
To see what worker MPM is see here.
I'd use dTrace to solve this mystery... if it was running on Solaris or Mac... but since Linux doesn't have it you might want to try their Systemtap, however I can't say anything about its usability since I haven't used it.
With dTrace you could easily sniff out the culprits within a day, and would hope with Systemtap it would be similiar
Another option that I can't assure you will do any good, but it's more than worth the effort. Is to read the detailed changelog for the new version, and review what might have changed that could remotely affect you.
Going through the changelogs has saved me more than once. Especially when some config options have changed and when something got deprecated. Worst case is it'll give you some clues as to where to look next