HUNTING DOWN
HUNTING DOWN
HUNTING DOWN
MEMORY LEAKS WITH
MEMORY LEAKS WITH
MEMORY LEAKS WITH
PHP MEMINFO
PHP MEMINFO
PHP MEMINFO
Benoit Jacquemont
@bjacquemont
Slide 2
Slide 2 text
What Is A Memory Leak?
A memory leak occurs when memory which
is no longer needed is not released.
en.wikipedia.org/wiki/Memory_leak
Slide 3
Slide 3 text
Memory Leaks: Should You Care?
Usually, PHP process life time = HTTP exchange lifetime
PHP process memory released a er each HTTP exchange
Yes but...
more and more capable-but-complex stacks
long running background jobs
Slide 4
Slide 4 text
Why I Care About Memory Leaks
E-COMMERCE
MOBILE APPLICATION
PRINT CATALOG
POINTS OF SALE
ERP
MEDIA SERVER
SUPPLIERS
PURCHASING DPT
MARKETING DPT
CSV
FTP
XML
XLS
SUPPLIERS
PORTAL
ENRIC
H
TRAN
SLATE
CO N T RO L
Import Jobs Export Jobs
Mass Edition Jobs
Rules Engine Jobs
...
Slide 5
Slide 5 text
The Effects Of A Memory Leak
Less memory available for other processes (surprise !)
The more memory your program uses, the slower it
becomes
Slide 6
Slide 6 text
But,
How Is Memory Released In PHP?
Slide 7
Slide 7 text
The Refcounter
Basic and efficient.
Frees memory as soon as it isn't used anymore.
Slide 8
Slide 8 text
No content
Slide 9
Slide 9 text
No content
Slide 10
Slide 10 text
No content
Slide 11
Slide 11 text
No content
Slide 12
Slide 12 text
No content
Slide 13
Slide 13 text
No content
Slide 14
Slide 14 text
No content
Slide 15
Slide 15 text
No content
Slide 16
Slide 16 text
No content
Slide 17
Slide 17 text
No content
Slide 18
Slide 18 text
No content
Slide 19
Slide 19 text
No content
Slide 20
Slide 20 text
No content
Slide 21
Slide 21 text
No content
Slide 22
Slide 22 text
No content
Slide 23
Slide 23 text
No content
Slide 24
Slide 24 text
No content
Slide 25
Slide 25 text
No content
Slide 26
Slide 26 text
1st object will be released only when 2nd object is released
2nd object will be released only when 1st object is released
Neither of them can be released by the refcounter...
The Refcounter Cannot Handle
Circular References
Slide 27
Slide 27 text
"Yeah sure, but circular references don't
exist in the real world..."
Tree structure:
parent → children → parent
Doctrine bidirectional mapping:
entity1 → entity2 → entity1
...
Slide 28
Slide 28 text
Circular Reference Collector
To The Rescue!
garbage collector exclusively dedicated to collect circular
references
Slide 29
Slide 29 text
But my memory usage keeps increasing!
function buildObjects()
{
$objA = new StdClass();
$objB = new StdClass();
$objA->attr = $objB;
$objB->attr = $objA;
}
for ($i = 0; $i < 2000; $i++) { buildObjects(); }
Slide 30
Slide 30 text
Keep Calm And Wait For The Collect!
There's a delay before the Collector cleans up memory
Slide 31
Slide 31 text
Circular Reference Collection
How It Works
Each time an object or array has its refcount decremented,
it gets added to the collector buffer.
Slide 32
Slide 32 text
Circular Reference Collection
How It Works
Slide 33
Slide 33 text
Circular Reference Collection
How It Works
Slide 34
Slide 34 text
Circular Reference Collection
How It Works
Slide 35
Slide 35 text
Circular Reference Collection
How It Works
Slide 36
Slide 36 text
Circular Reference Collection
How It Works
Slide 37
Slide 37 text
Circular Reference Collection
How It Works
Slide 38
Slide 38 text
Circular Reference Collection
How It Works
Slide 39
Slide 39 text
Circular Reference Collection
How It Works
Slide 40
Slide 40 text
Circular Reference Collection
How It Works
Slide 41
Slide 41 text
Circular Reference Collection
How It Works
Slide 42
Slide 42 text
Circular Reference Collection
How It Works
Slide 43
Slide 43 text
Circular Reference Collection
How It Works
Slide 44
Slide 44 text
Circular Reference Collection
How It Works
Slide 45
Slide 45 text
Refcounter +
Cycles Collector
=
Proper Cleanup Of Items
That Are Not Referenced
Anymore
Slide 46
Slide 46 text
Memory Leak
=
Items Non Needed Anymore
But Still Referenced, Directly
Or Indirectly,
By A Variable Still Alive
Slide 47
Slide 47 text
Let's Leak !
function buildObjects() {
$objA = new StdClass();
$objB = new StdClass();
$objA->attr = $objB;
$objB->attr = $objA;
return $objA;
}
$leakHolder = [];
for ($i = 0; $i < 200000; $i++) {
$object = buildObjects();
if ($i % 10 === 0) {
$leakHolder[] = $object;
}
}
Slide 48
Slide 48 text
GC + Memory Leak Perf Impacts
Slide 49
Slide 49 text
Why The Slow Down When The GC
Buffer Is Full Of Referenced Items?
Slide 50
Slide 50 text
Why The Slow Down When The GC
Buffer Is Full Of Referenced Items?
Slide 51
Slide 51 text
Why The Slow Down When The GC
Buffer Is Full Of Referenced Items?
Slide 52
Slide 52 text
Why The Slow Down When The GC
Buffer Is Full Of Referenced Items?
Each time a refcount is decremented,
your program is interrupted to rescan
the buffer!
Slide 53
Slide 53 text
Hunting Down Memory Leaks
from bird's eye view to ant's eye view
Slide 54
Slide 54 text
Hunting Memory Leaks
With Profilers
only provides information on when (at function level)
memory is taken or released
not on what or why
Slide 55
Slide 55 text
Hunting Memory Leaks
With PhpMeminfo
provides information on what so we can get to the why
faster
Slide 56
Slide 56 text
PHP Meminfo
MIT License
Two parts:
the extension itself, to dump memory content
analyzers to work with memory dump files
github.com/BitOne/php-meminfo
Slide 57
Slide 57 text
Import Example
Slide 58
Slide 58 text
Import Example - Data File
durgan.esta,maryjane82@blick.com,"Ms. Juliana Friesen"
gmorar,hessel.jarrod@gmail.com,"Tessie Haley"
norma11,maida55@hotmail.com,"Mr. Zack Sawayn"
Slide 59
Slide 59 text
Import Example
foreach ($fileContent as $data) {
$counter++;
$user = new User();
$user->setLogin($data[0]);
$user->setEmail($data[1]);
$user->setFullName($data[2]);
$this->getEntityManager()->persist($user);
if (0 === $counter % 1000) {
$this->getEntityManager()->flush();
}
}
$this->getEntityManager()->flush();
Why Is This Object Still In Memory?
$ bin/analyzer ref-path 0x2b46aa8 mem5000.json
Found 1 path(s)
Path to 0x2b46aa8
()$GLOBALS["kernel"]
->container
->services["doctrine.orm.default_entity_manager"]
->unitOfWork
->identityMap["AppBundle\Entity\User"]["9"]
Slide 65
Slide 65 text
Fixing The Leak!
....
$this->getEntityManager()->persist($user);
if (0 === $counter % 1000) {
$this->getEntityManager()->flush();
$this->getEntityManager()->clear('AppBundle\\Entity\\User');
}
...
Slide 66
Slide 66 text
Performances Before And A er Fix
Slide 67
Slide 67 text
Memory Leak - Good Practices
monitor your long running processes speed and memory
usage
avoid (or at least be aware of) stateful services
use a reasonable memory limit (not -1 !)
keep the number of items in memory at a low level