Introduction

In a previous article we learned about Creating a PHP Daemon Service. Now we are going to learn how to use methods to perform IPC - Inter-Process Communication - to communicate with daemon processes.

Message Queues

In the world of UNIX, there is an incredible variety of ways to send a message or a command to a daemon script and vice versa. But first I want to talk only about message queues - "System V IPC Messages Queues".

A long time ago I learned that a queue can be either in the System V IPC implementation, or in the POSIX implementation. I want to comment only about the System V implementation, as I know it better.

Lets get started. At the "normal" operating system level, queues are stored in memory. Queue data structures are available to all system programs. Just as in the file system, it is possible to configure queues access rights and message size. Usually a queue message size is small, less than 8 KB.

This introductory part is over. Lets move on to the practice with same example scripts.queue-send.php

$key = ftok(__FILE__, 'A'); 
$queue = msg_get_queue($key);

msg_send($queue, 1, 'message, type 1');
msg_send($queue, 2, 'message, type 2');
msg_send($queue, 3, 'message, type 3');
msg_send($queue, 1, 'message, type 1');

echo "send 4 messages
";

queue-receive.php

$key = ftok('queue-send.php', 'A');
$queue = msg_get_queue($key);

for ($i = 1; $i <= 3; $i++) {
 echo "type: {$i}
";

 while ( msg_receive($queue, $i, $msgtype, 4096, $message, false, MSG_IPC_NOWAIT) ) {
 echo "type: {$i}, msgtype: {$msgtype}, message: {$message}
";
 }
}

Lets run on the first stage of the file queue-send.php, and then queue-receive.php.

u% php queue-send.php
send 4 messages
u% php queue-receive.php
type: 1
type: 1, msgtype: 1, message: s:15:"message, type 1";
type: 1, msgtype: 1, message: s:15:"message, type 1";
type: 2
type: 2, msgtype: 2, message: s:15:"message, type 2";
type: 3
type: 3, msgtype: 3, message: s:15:"message, type 3";

You may notice that the messages have been grouped. The first group gathered 2 messages of the first type, and then the remaining messages.

If we would have indicated to receive messages of type 0, you would get all messages, regardless of the type.

while (msg_receive($queue, $i, $msgtype, 4096, $message, false, MSG_IPC_NOWAIT)) {

Here it is worth noting another feature of the queues: if we do not use the constant MSG_IPC_NOWAIT in the script and run the script queue-receive.php from a terminal, and then run periodically the file queue-send.php, we see how a daemon can effectively use this to wait jobs.queue-receive-wait.php

$key = ftok('queue-send.php', 'A');
$queue = msg_get_queue($key);

while ( msg_receive($queue, 0, $msgtype, 4096, $message) ) {
 echo "msgtype: {$msgtype}, message: {$message}
";
}

Actually that is the most interesting information of all I have said. There are also functions to get statistics, disposal and checking for the existence of queues.

Lets now try to write a daemon listening to a queue:queue-daemon.php

$pid = pcntl_fork();
$key = ftok('queue-send.php', 'A');
$queue = msg_get_queue($key);

if ($pid == -1) {
 exit;
} elseif ($pid) {
 exit;
} else {
 while ( msg_receive($queue, 0, $msgtype, 4096, $message) ) {
 echo "msgtype: {$msgtype}, message: {$message}
";
 }
}

posix_setsid();

Shared Memory

We have learned to work with queues, with which you can send small system messages. But then we may certainly be faced with the task of transmitting large amounts of data. My favorite type of system, System V, has solved the problem of rapid transmission and preservation of large data in memory using a mechanism calledShared Memory.

In short, the data in the Shared Memory lives until the system is rebooted. Since the data is in memory, it works much faster than if it was stored in a database somewhere in a file, or, God forgive me on a network share.

Lets try to write a simple example of data storage.shared-memory-write-base.php

$id = ftok(__FILE__, 'A');


$shmId = shm_attach($id);

$var = 1;

if (shm_has_var($shmId, $var)) {
 $data = (array) shm_get_var($shmId, $var);
} else {
 $data = array();
}

$data[time()] = file_get_contents(__FILE__);

shm_put_var($shmId, $var, $data);

Run this script several times to save the value in memory. Now lets write a script only to read from the memory.shared-memory-read-base.php

$id = ftok(__DIR__ . '/shared-memory-write-base.php', 'A');
$shmId = shm_attach($id);
$var = 1; 

if (shm_has_var($shmId, $var)) {
 $data = (array) shm_get_var($shmId, $var);
} else {
 $data = array();
}

foreach ($data as $key => $value) {
 $path = "/tmp/$key.php";
 file_put_contents($path, $value);

 echo $path . PHP_EOL;
} 

Semaphores

So, in general terms, it should be clear for you by now how to work with shared memory. The only problems left to figure out are about a couple of nuances, such as: "What to do if two processes want to record one block of memory?" Or "How to store binary files of any size?".

To prevent simultaneous accesses we will use semaphores. Semaphores allow us to flag that we want to have exclusive access to some resource, like for instance a shared memory block. While that happens other processes will wait for their turn on semaphore.

In this code it explained clearly:shared-memory-semaphors.php

$id = ftok(__FILE__, 'A');

$semId = sem_get($id);

sem_acquire($semId);

$data = file_get_contents(__DIR__.'/06050396.JPG', FILE_BINARY);

$shmId = shm_attach($id, strlen($data)+4096);
$var = 1;
 
if (shm_has_var($shmId, $var)) {
 $data = shm_get_var($shmId, $var);

 $filename = '/tmp/' . time();
 file_put_contents($filename, $data, FILE_BINARY);

 shm_remove($shmId);
} else {
 shm_put_var($shmId, $var, $data); 
}

sem_release($semId); 

Now you can use the md5sum command line utility to compare two files, the original and the saved file. Or, you can open the file in image editor or whatever prefer to compare the images.

With this we are done with shared memory and semaphores. As your homework I want to ask you to write code that a demon will use semaphores to access shared memory.

Conclusion

Exchanging data between the daemons is very simple. This article described two options for data exchange: message queues and shared memory.

Post a comment here if you have questions or comments about how to exchange data with daemon services in PHP.

Now that the Thanksgiving and Black Friday are left behind, we're all back at our desks, some of us having PHPStorm open for the whole day. In this post, I'll say a few words on this beautiful IDE, PHPUnit and XDebug.
You know that unit tests are essential, don't you? So do the PHPStorm developers. This industry-standard level IDE has tons of capabilities for integrating test frameworks and debuggers into your project. Even if you use VMs or containers to run your development environment, chances are they got you covered!



I often see even experienced PHP programmers debugging their code with var_dump(), which is obviously not the best way to do it. If you see the code for the first time, if you work with legacy code - step-by-step interactive debugging is the way to go. Sometimes it can save you hours of old school var_dumping.

As of unit tests, I often hear that it's good enough to run tests from the terminal. I even know a guy who runs watch phpunit /path/to/test while developing: this way the test is run every 2 seconds, you switch to the terminal whenever you want to see the latest results and that's it. However, there are certain advantages in running tests from the IDE. First, it's super-handy to launch a test method, test class or a whole folder with tests, just by pressing a hotkey. Second, the test results appear right there, in PHPStorm, with failures and their stack traces, every entry clickable and takes you directly to the file:line where a nasty thing happened. I also find the ability to run a debugger for a unit test, extremely attractive. Test fails, you click on a trace entry, get to a problematic line, place a break point, re-run the test in debug mode - and there you go.

For all those integrations, you will first need to setup the PHP interpreter for the project: Configuring PHP Development Environment. You will find both local and remote interpreter setups. "Local" is the PHP that you have on your workstation, the host machine. "Remote" can be pretty much everything: SSH if your Dev environment runs on a shared sandbox for all developers, docker or docker-compose if you run it using docker containers.

Next step - creating PHPUnit configuration. Go toSettings -> Languages and Frameworks -> PHP -> Test Frameworks. Follow this guide, it has much more information which will be more up-to-date than this post.Don't forget to set Path Mappings for your remote environments! That is, you probably have your project in, say, $HOME/projects/cool-project, but inside a docker or on a remote host it might be located at /app or /var/www, then you have to let PHPStorm know about this.

Once you're done with PHPUnit setup, you can finally run your tests! The default shortcut on my Linux machine isCtrl+Shift+F10 (shortcuts are usually different on Mac though). Place a cursor inside a test method, press the shotcut: PHPStorm will launch PHPUnit withthat particular test method! When the cursor in a scope of test class but not inside a test method - the whole test class will be run. And, you also can select a whole folder with tests, in the project tree and run it, ain't that cool?

A small tip for the docker-compose lovers. When I first set PHPStorm integration with docker-compose and ran the tests, I was quite surprised (unpleasantly) to see that myphp-fpm service that I was connecting to, is gone after the test process is finished. Took me some time to figure out that it's PHPStorm's expected behavior. It stops the target service after it's done testing. A workaround I started to use is as follows: I just add another service calledphpunit which uses a php-fpm or php-cli image, and is not needed by anything except unit testing in PHPStorm.

Now to debugging.

Debugging is like being the detective in a crime movie where you are also the murderer. Filipe Fortes a.k.a. @fortes

Obviously, your PHP interpreter in development environment will need a debugger extension in order for you to debug interactively. PHPStorm support the two most widely used options: XDebug and Zend Debugger. When using docker I usually make a separate Dockerfile for development, using production image as base, then add development tools,XDebug being the most important. Honestly, I've never usedZend Debugger, so have little to tell about its' nuances.

Got an extension? Go to Debugging Ultimate Guide! Debugger settings in PHPStorm are atSettings -> Languages and Frameworks -> PHP -> Debug. Most of the time you don't need to change them.Again, a note for docker-compose users. There is an XDebug setting that allow debugger to resolve the client (PHPStorm) IP address:xdebug.remoteconnect_back_. That's a disappointment but those will not work, at least with a default docker-compose setup. Thing is, all containers in a compose stack are running behind a network proxy provided by docker-compose. That is, the REMOTE_ADDR for all the containers will always be the IP of proxy. A workaround:

* disablexdebug.remoteconnect_back_;
* add.user.ini to the application root folder with the following contents:xdebug.remotehost = 192.168.X.X_ (your machine's IP address in the LAN). It's generally a good idea to exclude.user.ini from VCS control.

As a conclusion: if you still usevardump()_ to debug, stop living in the stone age, upgrade your knowledge and become more productive! If you don't write unit tests, start doing it. If your managers say it's a waste of time, tell them that it's coding without tests that is a waste of time. And, if you find this post of any use, or have an opinion, or a question - please do comment!

What is a Daemon?

The term daemon was coined by the programmers of Project MAC at MIT. It is inspired on Maxwell's demon in charge of sorting molecules in the background. The UNIX systems adopted this terminology for daemon programs.

It also refers to a character from Greek mythology that performs the tasks for which the gods do not want to take. As stated in the "Reference System Administrator UNIX", in ancient Greece, the concept of "personal daemon" was, in part, comparable to the modern concept of "guardian angel." BSD family of operating systems use the image as a demon's logo.

Daemons are usually started at machine boot time. In the technical sense, a demon is considered a process that does not have a controlling terminal, and accordingly there is no user interface. Most often, the ancestor process of the deamon is init - process root on UNIX, although many daemons run from special rcd scripts started from a terminal console.

Richard Stevenson describes the following steps for writing daemons:
    . Resetting the file mode creation mask to 0 function umask(), to mask some bits of access rights from the starting process.
    . Cause fork() and finish the parent process. This is done so that if the process was launched as a group, the shell believes that the group finished at the same time, the child inherits the process group ID of the parent and gets its own process ID. This ensures that it will not become process group leader.
    . Create a new session by calling setsid(). The process becomes a leader of the new session, the leader of a new group of processes and loses the control of the terminal.
    . Make the root directory of the current working directory as the current directory will be mounted.
    . Close all file descriptors.
    . Make redirect descriptors 0,1 and 2 (STDIN, STDOUT and STDERR) to /dev/null or files /var/log/project_name.out because some standard library functions use these descriptors.
    . Record the pid (process ID number) in the pid-file: /var/run/projectname.pid.
    . Correctly process the signals and SigTerm SigHup: end with the destruction of all child processes and pid - files and / or re-configuration.

How to Create Daemons in PHP

To create demons in PHP you need to use the extensions pcntl and posix. To implement the fast communication withing daemon scripts it is recommended to use the extension libevent for asynchronous I/O.

Lets take a closer look at the code to start a daemon:

umask(0);
$pid = pcntl_fork(); 
if ($pid < 0) {
 print('fork failed');
 exit 1; 
}

After a fork, the execution of the program works as if there are two branches of the code, one for the parent process and the second for the child process. What distinguishes these two processes is the result value returned the fork() function call. The parent process ID receives the newly created process number and the child process receives a 0.

if ($pid > 0) { echo "daemon process started
";
 exit;
} 
 
$sid = posix_setsid();
if ($sid < 0) {
 exit 2;
}

chdir('/');
file_put_contents($pidFilename, getmypid() ); 
run_process();

The implementation of step 5 "to close all file descriptors" can be done in two ways. Well, closing all file descriptors is difficult to implement in PHP. You just need to open any file descriptors before fork(). Second, you can override the standard output to an error log file using init_set() or use buffering using ob_start() to a variable and store it in log file:

ob_start();
var_dump($some_object);
$content = ob_get_clean();
fwrite($fd_log, $content); 

Typically, ob_start() is the start of the daemon life cycle and ob_get_clean() and fwrite() calls are the end. However, you can directly override STDIN, STDOUT and STDERR:

ini_set('error_log', $logDir.'/error.log');
fclose(STDIN); 
fclose(STDOUT);
fclose(STDERR);
$STDIN = fopen('/dev/null', 'r'); 
$STDOUT = fopen($logDir.'/application.log', 'ab');
$STDERR = fopen($logDir.'/application.error.log', 'ab');

Now, our process is disconnected from the terminal and the standard output is redirected to a log file.

Handling Signals

Signal processing is carried out with the handlers that you can use either via the library pcntl (pcntl_signal_dispatch()), or by using libevent. In the first case, you must define a signal handler:

function sig_handler($signo)
{
 global $fd_log;
 switch ($signo) {
 case SIGTERM:
 fclose($fd_log); unlink($pidfile); exit;
 break;
 case SIGHUP:
 init_data(); break;
 default:
 }
}


pcntl_signal(SIGTERM, "sig_handler");
pcntl_signal(SIGHUP, "sig_handler");

Note that signals are only processed when the process is in an active mode. Signals received when the process is waiting for input or in sleep mode will not be processed. Use the wait function pcntl_signal_dispatch(). We can ignore the signal using flag SIG_IGN: pcntl_signal(SIGHUP, SIG_IGN); Or, if necessary, restore the signal handler using the flag SIG_DFL, which was previously installed by default: pcntl_signal(SIGHUP, SIG_DFL);

Asynchronous I/O with Libevent

In the case you use blocking input / output signal processing is not applied. It is recommended to use the library libevent which provides non-blocking as input / output, processing signals, and timers. Libevent library provides a simple mechanism to start the callback functions for events on file descriptor: Write, Read, Timeout, Signal.

Initially, you have to declare one or more events with an handler (callback function) and attach them to the basic context of the events:

$base = event_base_new();
$event = event_new();
$errno = 0;
$errstr = '';
$socket = stream_socket_server("tcp://$IP:$port", $errno, $errstr);
stream_set_blocking($socket, 0);
event_set($event, $socket, EV_READ | EV_PERSIST, 'onAccept', $base);

Function handlers 'onRead', 'onWrite', 'onError' must implement the processing logic. Data is written into the buffer, which is obtained in the non-blocking mode:

function onRead($buffer, $id)
{
 while($read = event_buffer_read($buffer, 256)) {
 var_dump($read);
 }
}

The main event loop runs with the function event_base_loop($base);. With a few lines of code, you can exit the handler only by calling: event_base_loobreak(); or after the specified time (timeout) event_loop_exit();.

Error handling deals with failure Events:

function onError($buffer, $error, $id)
{
 global $id, $buffers, $ctx_connections;
 event_buffer_disable($buffers[$id], EV_READ | EV_WRITE);
 event_buffer_free($buffers[$id]);
 fclose($ctx_connections[$id]);
 unset($buffers[$id], $ctx_connections[$id]);
}

It should be noted the following subtlety: Working with timers is only possible through the file descriptor. The example of official the documentation does not work. Here is an example of processing that runs at regular intervals.

$event2 = event_new();
$tmpfile = tmpfile();
event_set($event2, $tmpfile, 0, 'onTimer', $interval);
$res = event_base_set($event2, $base);
event_add($event2, 1000000 * $interval);

With this code we can have a working timer finishes only once. If we need a "permanent" Timer, using the function onTimer we need create a new event each time, and reassign it to process through a "period of time":

function onTimer($tmpfile, $flag, $interval)
{
 $global $base, $event2;

 if ($event2) {
 event_delete($event2);
 event_free($event2);
 }

 call_user_function(‘process_data’,$args);

 $event2 = event_new();
 event_set($event2, $tmpfile, 0, 'onTimer', $interval);
 $res = event_base_set($event2, $base);
 event_add($event2, 1000000 * $interval);
}

At the end of the daemon we must release all previously allocated resources:

event_delete($event);
event_free($event);
event_base_free($base);

event_base_set($event, $base);
event_add($event);

Also it should be noted that for the signal processing handler is set the flag EV_SIGNAL: event_set($event, SIGHUP, EV_SIGNAL, 'onSignal', $base);

If needed constant signal processing, it is necessary to set a flag EV_PERSIST. Here follows a handler for the event onAccept, which occurs when a new connection is a accepted on a file descriptor:

function onAccept($socket, $flag, $base) {
 global $id, $buffers, $ctx_connections;
 $id++;
 $connection = stream_socket_accept($socket);
 stream_set_blocking($connection, 0);
 $buffer = event_buffer_new($connection, 'onRead', NULL, 'onError', $id);
 event_buffer_base_set($buffer, $base);
 event_buffer_timeout_set($buffer, 30, 30);
 event_buffer_watermark_set($buffer, EV_READ, 0, 0xffffff); event_buffer_priority_set($buffer, 10); event_buffer_enable($buffer, EV_READ | EV_PERSIST); $ctx_connections[$id] = $connection;
 $buffers[$id] = $buffer;
}

Monitoring a Daemon

It is good practice to develop the application so that it was possible to monitor the daemon process. Key indicators for monitoring are the number of items processed / requests in the time interval, the speed of processing with queries, the average time to process a single request or downtime.

With the help of these metrics can be understood workload of our demon, and if it does not cope with the load it gets, you can run another process in parallel, or for running multiple child processes.

To determine these variables need to check these features at regular intervals, such as once per second. For example downtime is calculated as the difference between the measurement interval and total time daemon.

Typically downtime is determined as a percentage of a measurement interval. For example, if in one second were executed 10 cycles with a total processing time of 50ms, the time will be 950ms or 95%.

Query performance wile be 10rps (request per second). Average processing time of one request: the ratio of the total time spent on processing requests to the number of requests processed, will be 5ms.

These characteristics, as well as additional features such as memory stack size queue, number of transactions, the average time to access the database, and so on.

An external monitor can be obtain data through a TCP connection or unix socket, usually in the format of Nagios or zabbix, depending on the monitoring system. To do this, the demon should use an additional system port.

As mentioned above, if one worker process can not handle the load, usually we run in parallel multiple processes. Starting a parallel process should be done by the parent master process that uses fork() to launch a series of child processes.

Why not run processes using exec() or system()? Because, as a rule, you must have direct control over the master and child processes. In this case, we can handle it via interaction signals. If you use the exec command or system, then launch the initial interpreter, and it has already started processes that are not direct descendants of the parent process.

Also, there is a misconception that you can make a demon process through command nohup. Yes, it is possible to issue a command: nohup php mydaemon.php -master >> /var/log/daemon.log 2 >> /var/log/daemon.error.log &

But, in this case, would be difficult to perform log rotation, as nohup "captures" file descriptors for STDOUT / STDERR and release them only at the end of the command, which may overload of the process or the entire server. Overload demon process may affect the integrity of data processing and possibly cause partial loss of some data.

Starting a Daemon

Starting the daemon must happen either automatically at boot time, or with the help of a "boot script."

All startup scripts are usually in the directory /etc/rc.d. The startup script in the directory service is made /etc/init.d/ . Run command start service myapp or start group /etc/init.d/myapp depending on the type of OS.

Here is a sample script text:

#! /bin/sh
#
$appdir = /usr/share/myapp/app.php
$parms = --master –proc=8 --daemon
export $appdir
export $parms
if [ ! -x appdir ]; then
 exit 1
fi

if [ -x /etc/rc.d/init.d/functions ]; then
 . /etc/rc.d/init.d/functions
fi

RETVAL=0

start () {
 echo "Starting app"
 daemon /usr/bin/php $appdir $parms 
 RETVAL=$?
 [ $RETVAL -eq 0 ] && touch /var/lock/subsys/mydaemon
 echo
 return $RETVAL
}

stop () {
 echo -n "Stopping $prog: "
 killproc /usr/bin/fetchmail
 RETVAL=$?
 [ $RETVAL -eq 0 ] && rm -f /var/lock/subsys/mydaemon
 echo
 return $RETVAL
}

case in
 start)
 start
 ;;
 stop)
 stop
 ;;
 restart)
 stop
 start
 ;;
 status)
 status /usr/bin/mydaemon
 ;;
 *)
 echo "Usage: 

php
if (is_file('app.phar')) {
unlink('app.phar');
}
$phar = new Phar('app.phar', 0, 'app.phar');
$phar->compressFiles(Phar::GZ);
$phar->setSignatureAlgorithm (Phar::SHA1);
$files = array();
$files['bootstrap.php'] = './bootstrap.php';
$rd = new RecursiveIteratorIterator(new RecursiveDirectoryIterator('.'));
foreach($rd as $file){
if ($file->getFilename() != '..' && $file->getFilename() != '.' && $file->getFilename() != __FILE__) {
if ( $file->getPath() != './log'&& $file->getPath() != './script'&& $file->getPath() != '.')
$files[substr($file->getPath().DIRECTORY_SEPARATOR.$file->getFilename(),2)] =
$file->getPath().DIRECTORY_SEPARATOR.$file->getFilename();
}
}
if (isset($opt['version'])) {
$version = $opt['version'];
$file = "buildFromIterator(new ArrayIterator($files));
$phar->setStub($phar->createDefaultStub('bootstrap.php'));
$phar = null;
}

 {start|stop|restart|status}"
 ;;
 
RETVAL=$?
exit $RETVAL

Distributing Your PHP Daemon

To distribute a daemon it is better to pack it in a single phar archive module. The assembled module should include all the necessary PHP and .ini files.

Below is a sample build script:

#php app.phar
myDaemon version 0.1 Debug
usage:
--daemon – run as daemon
--debug – run in debug mode
--settings – print settings
--nofork – not run child processes
--check – check dependency modules
--master – run as master
--proc=[8] – run child processes

Additionally, it may be advisable to make a PEAR package as a standard unix-console utility that when run with no arguments prints its own usage instruction:
[NMD%%CODE%%]

Conclusion

Creating daemons in PHP it is not hard but to make them run correctly it is important to follow the steps described in this article.

Post a comment here if you have questions or comments on how to create daemon services in PHP.

For those of you not familiar with the concept of underclocking: it's the opposite of overclocking, that is, you don't speed up CPU but instead slow it down..

What for?

Ask the underclockers, I'm totally not sure. Actually, hanging around the Web these days leaves a feeling that nearly every website out there must have been underclocked, but most of the time it's about tons of unnecessary images, megabytes of javascript (of which hardly a hundred kilobytes gets actually executed), and all that. In this post I will, however, tell you about a server-side approach to underclocking, with a help of our good old friend - the MySQL Database Server.

Today I had a nice chat in my client's development telegram channel. The two other devs, R** and V**, were making a switch of the old image API app to a new MySQL server. A couple of days before that, we have discussed a plan, it was as dumb as possible, just as I like it. Super-simple clear steps that a five-year-old can make. Switch to readonly mode (stop uploads), dump DB, restore the dump on the new server, update database connection details, turn off readonly mode. What could possibly go wrong?

Nothing. Except that it did go wrong. The app that I'm talking about, is a really ancient piece of what is gently called "legacy". Once the app was back to normal again, we noticed a significant slowdown on every page that made use of images. Before that point, I never got to that app and/or its database. I logged in to the MySQL console, and started investigating, at the same point chatting with colleagues.

Me: Is that really important that the tables are MyISAM? It's 2018, you know.. There are dozens of queries in queue waiting for table-level locks.

R**: Are they MyISAM? Really?

Me: Yes.. Any objection against converting them to InnoDB? With the current state of the website, with all those tons of Gateway Timeouts, it's not going to make it worse if I do it right now..

    . minutes later:

Me: Nah, it didn't help a lot.. But, looking at the SHOW PROCESSLIST output, I see something weird. What, do you think, this query does? SELECT LAST_INSERT_ID() FROM images? 

R**: ehh... Gets you the last AUTO_INCREMENT id from images table?

Me: Let's play another good news bad news joke.. Good news: you're right, it gets you the last AUTO_INCREMENT id. Bad news: it's not for table, it's for the session. Worse news: this query gets you the last AUTO_INCREMENT id and does it exactly as many times as there are rows in the images table. how many are there?

R**: about 8mln. #@%&! It's sending 8mln rows on every image upload, through the network!

Me: Bingo! 8mln rows, with one and the same integer value in all of them.

R**: Ouch... Aaaand... Before today, it was not an issue. Because the database was on the same server as the application..

Me: Exactly, it used the loopback interface, and now it's using ehternet, which, apparently, doesn't have a super good bandwidth. We don't have a gigabit channel between servers, do we?

R**: No, it's 100 Mbit

Me: Are you fixing the query, BTW?

R**: yeah, man, deploying it...

Another 10 minutes later, problem is gone, performance is back to normal.

What conclusions can one make from this story?

I can think of two at least:
First: never underestimate legacy code. The ways it can move to bite you in the ass, are mysterious.
Second: if you're working with MySQL or another RDBMS, learn SQL, learn the specific SQL dialect you're using and learn how to trouble shoot issues. In this case, I did not need to look in the PHP code at all in order to help my fellow colleagues out. You can also generalize this principle as "you have to know the tools you're using".

Happy optimizing, folks! Comments appreciated!

It's 2018, and you're a top-notch modern web developer, with a load of knowledge and tools right there at your disposal: Google and StackOverflow, debugger with a GUI, IDE with autocomplete, you name it. Occasionally, though, you still find yourself in a plain old text console on a remote server, or you have to do something without IDE, or there is no network connection... In such cases it might be helpful to feel comfortable in a simple terminal. In this post I'm going to list some switches for the PHP command that you can use to get information and some utilities.

Getting basic information about PHP

$ php -i
phpinfo()
PHP Version => 7.2.10-0ubuntu1

System => Linux awesome 4.18.0-10-generic #11-Ubuntu SMP Thu Oct 11 15:13:55 UTC 2018 x86_64
Build Date => Sep 13 2018 13:38:55
Server API => Command Line Interface
Virtual Directory Support => disabled
...

Full information about your PHP interpreter. Pipe the output to the Unix less command in order to get pagination and search: php -i | less. Type Q to exit the less shell. Some distros might lack less, in that case you may try php -i | more, which doesn't give you search but still has pagination.

Want a short summary of which PHP extensions you have? Just ask:

$ php -m
[PHP Modules]
calendar
Core
ctype
date
dom
ds
exif
...

More specific info about core and extensions' functions and classes

Full information about functions and classes provided by an extension:

$ php --re ds
Extension [ <persistent> extension #46 ds version 1.2.6 ] {

 - Dependencies {
 Dependency [ json (Required) ]
 Dependency [ spl (Required) ]
 }

 - Classes [11] {
 Interface [ <internal:ds> interface Ds\Hashable ] {

 - Constants [0] {
 }

 - Static properties [0] {
 }
...

Information on a specific class:

$ php --rc Ds\Vector
Class [ <internal:ds> <iterateable> final class Ds\Vector implements Ds\Sequence, Traversable, Countable, JsonSerializable, Ds\Collection ] {

 - Constants [1] {
 Constant [ public integer MIN_CAPACITY ] { 8 }
 }

 - Static properties [0] {
 }
...

Same for a function:

$ php --rf fopen
Function [ <internal:standard> function fopen ] {

 - Parameters [4] {
 Parameter #0 [ <required> $filename ]
 Parameter #1 [ <required> $mode ]
 Parameter #2 [ <optional> $use_include_path ]
 Parameter #3 [ <optional> $context ]
 }
}

Utilities

Ever found yourself creating a dummy PHP file of just a few lines - only to be run once and then deleted? The -a switch might be what you're looking for:

$ php -a
Interactive mode enabled

php > var_dump(join(", ", [1, 2, 3]));
php shell code:1:
string(7) "1, 2, 3"
php > 

It starts an interactive shell so you can type any PHP code and execute it straight away. Requires PHP to be compiled with readline support (most distros have that anyway).

Want a quick check for any parse/syntax errors in a PHP file? Use linter:

$ php -l test.php 
PHP Parse error: syntax error, unexpected 'array_shift' (T_STRING) in test.php on line 4
Errors parsing test.php

It has a web-server!

Yes! Just in case you missed it, as of PHP 5.4.0, the CLI SAPI provides a built-in web server. Want a quick look at a web page generated by an app? Here you go:

$ cd /my_application/document_root
$ php -S localhost:8000

Then open http://localhost:8000/ in your browser of choice and enjoy!

Hope you also have enjoyed this reading. Your feedback and questions are always appreciated!