While investigating a long running perl program for memory leaks I tried to use Test::LeakTrace.
Looking at one of the leaks it reports I can narrow down the leaking code to just:
/$?/
So running: perl -MTest::LeakTrace::Script -e'/$?/' prints:
leaked SCALAR(0x10d3d48) from -e line 1.
Why is this, do I need to worry about it ?
Update: Also tried Devel::LeakTrace::Fast, it's not complaining about the same code.
Assuming you got a leak. Then this:
perl -e'/$?/ for 1..1E9'
should make your process grow in memory
ps -o rss,vsz <PID>
In my case it stays stable all the way. You should check it for your setup. It could be that leak your module detects is some late destruction. You could write a note to the module authors to help you figure out its output, you can help them to improve it...
BTW another thing confirming "no leak" for me is that on
perl -MTest::LeakTrace::Script -e'/$?/ for 1..1000'
I don't see multiple leaked scalars, just one.
Related
I have a Perl script, fetch url like http://1.1.1.1/1.jpg from MySQL using DBI, and download this jpg file using LWP::Simple. It's a infinite loop.
while (1) {
my $url=&fetch_url_from_mysql;
if ($url){
&download_jpg($url);
} else {
sleep 1;
}
}
Plain simple. I suppose the memory usage would be stay in certain amount. But after one month of continuous running of this script. The memory usage is 7.5G!
How can I profile it?
For profiling, set an explitict exit. Create a counter, and exit from your program if your iteration is equal or bigger than this.
For profiling, use NYTprof:
perl -d:NYTProf script.pl
nytprofhtml
But you are dealing with a memory leak here.
Read this to find a memory leak: How can I find memory leaks in long-running Perl program?
Most probably you have a variable that will never be freed. Perl frees memory if a variable goes out of scope, but one of your variables never goes out of scope.
Use $variable=undef to free up the memory.
If you port your whole script maybe we could find a leak in it.
regards,
We have a pretty big perl codebase.
Some processes that run for multiple hours (ETL jobs) suddenly started consuming a lot more RAM than usual. Analysis of the changes in the relevant release is a slow and frustrating process. I am hoping to identify the culprit using more automated analysis.
Our live environment is perl 5.14 on Debian squeeze.
I have access to lots of OS X 10.5 machines, though. Dtrace and perl seem to play together nicely on this platform. Seems that using dtrace on linux requires a boot more work. I am hoping that memory allocation patterns will be similar between our live system and a dev OS X system - or at least similar enough to help me find the origin of this new memory use.
This slide deck:
https://dgl.cx/2011/01/dtrace-and-perl
shows how to use dtrace do show number of calls to malloc by perl sub. I am interested in tracking the total amount of memory that perl allocates while executing each sub over the lifetime of a process.
Any ideas on how this can be done?
There's no single way to do this, and doing it on a sub-by-sub basis isn't always the best way to examine memory usage. I'm going to recommend a set of tools that you can use, some work on the program as a whole, others allow you to examine a single section of your code or a single variable.
You might want to consider using Valgrind. There's even a Perl module called Test::Valgrind that will help set up a suppression file for your Perl build, and then check for memory leaks or errors in your script.
There's also Devel::Size which does exactly what you asked for, but on a variable-by-variable basis rather than a sub-by-sub basis.
You can use Devel::Cycle to search for inadvertent circular memory references in complex data structures. While a circular reference doesn't mean that you're wasting memory as you use the object, circular references prevent anything in the chain from being freed until the cycle is broken.
Devel::Leak is a little bit more arcane than the rest, but it basically will allow you to get full information on any SVs that are created and not destroyed between two points in your program's execution. If you check this across a sub call, you'll know any new memory that that subroutine allocated.
You may also want to read the perldebguts section of the Perl manual.
I can't really help more because every codebase is going to wind up being different. Test::Valgrind will work great for some codebases and terribly on others. If you are going to try it, I recommend you use the latest version of Valgrind available and Perl >= 5.10, as Perl 5.8 and Valgrind historically didn't get along too well.
You might want to look at Memory::Usage and Devel::Size
To check the whole process or sub:
use Memory::Usage;
my $mu = Memory::Usage->new();
# Record amount of memory used by current process
$mu->record('starting work');
# Do the thing you want to measure
$object->something_memory_intensive();
# Record amount in use afterwards
$mu->record('after something_memory_intensive()');
# Spit out a report
$mu->dump();
Or to check specific variables:
use Devel::Size qw(size total_size);
my $size = size("A string");
my #foo = (1, 2, 3, 4, 5);
my $other_size = size(\#foo);
my $foo = {
a => [1, 2, 3],
b => {a => [1, 3, 4]}
};
my $total_size = total_size($foo);
The answer to the question is 'yes'. Dtrace can be used to analyze memory usage in a perl process.
This snippet of code:
https://github.com/astletron/perl-dtrace-malloc/blob/master/perl-malloc-total-bytes-by-sub.d
tracks how memory use increases between the call and return of every sub in a program. As an added bonus, dtrace seems to sort the output for you (at least on OS X). Cool.
Thanks to all that chimed in. I answered this one myself as the question is really specific to dtrace/perl.
You could write a simple debug module based on Devel::CallTrace that prints the sub entered as well as the current memory size of the current process. (Using /proc or whatever.)
I've slurped in a big file using File::Slurp but given the size of the file I can see that I must have it in memory twice or perhaps it's getting inflated by being turned into 16 bit unicode. How can I best diagnose that sort of a problem in Perl?
The file I pulled in is 800mb in size and my perl process that's analysing that data has roughly 1.6gb allocated at runtime.
I realise that I may be wrong about my reason for the problem but I'm not sure the most efficient way to prove/disprove my theory.
Update:
I have elminated dodgy character encoding from the list of suspects. It looks like I'm copying the variable at some point, I just can't figure out where.
Update 2:
I have now done some more investigation and discovered that it's actually just getting the data from File::Slurp that's causing the problem. I had a look through the documentation and discovered that I can get it to return a scalar_ref, i.e.
my $data = read_file($file, binmode => ':raw', scalar_ref => 1);
Then I don't get the inflation of my memory. Which makes some sense and is the most logical thing to do when getting the data in my situation.
The information about looking at what variables exist etc. has generally helpful though thanks.
Maybe Devel::DumpSizes and/or Devel::Size can help out? I think the former would be more useful in your case.
Devel::DumpSizes - Dump the name and size in bytes (in increasing order) of variables that are available at a give point in a script.
Devel::Size - Perl extension for finding the memory usage of Perl variables
Here are some generic resources on memory issues in Perl:
http://perl.active-venture.com/pod/perldebguts-perlmemory.html
Perl memory usage profiling and leak detection?
How can I find memory leaks in long-running Perl program?
As far as your own suggestion, the simplest way to disprove would be to write a simple Perl program that:
Creates a big (100M) file of plain text, probably by just outputting the same string in a loop into a file, or for binary files running dd command via system() call
Read the file in using standard Perl open()/#a=<>;
Measure memory consumption.
Then repeat #2-#3 for your 800M file.
That will tell you if the issue is File::Slurp, some weird logic in your program, or some specific content in the file (e.g. non-ascii, although I'd be surprized if that ends up to be the reason)
I'm trying to enable the garbage collector of my script to do a better job. There's a ton of memory that it should be able to reclaim, but something is stopping it.
I've used Devel::Cycle a bit and that's allowed me to get closer but I'm not quite there.
How do I find out the current reference count for a Perl hash (the storage for my objects)?
Is there a way to track who is holding a reference to an object? Perhaps a sort of Tie that says, whenever someone points are this object, remember who that someone is.
You are looking for Devel::Refcount.
If you are worried about returning unused memory to the OS, you should know that is not possible in general. The memory footprint of your Perl program will be proportional to the largest allocation during the lifetime of your program.
See How can I make my Perl program take less memory? in the Perl FAQ list as well as Mini-Tutorial: Perl's Memory Management (as pointed out by #Evan Carroll in the comments).
SOLVED see Edit 2
Hello,
I've been writing a Perl program to handle automatic upgrading of local (proprietary) programs (for the company I work for).
Basically, it runs via cron, and unfortunately has a memory leak (or something similar). The problem is that the leak only happens when I'm not looking (aka when run via cron, not via command line).
My code does not contain any circular (or other) references, so the commonly cited tools will not help me (Devel::Cycle, Devel::Peek).
How would I go about figuring out what is using so much memory that the kernel kills it?
Basically, the code SFTPs into a server (using ```sftp...`` `), calls OpenSSL to verify the file, and then SFTPs more if more files are needed, and installs them (untars them).
I have seen delays (~15 sec) before the first SFTP session, but it has never used so much memory as to be killed (in my presence).
If I can't sort this out, I'll need to re-write in a different language, and that will take precious time.
Edit: The following message is printed out by the kernel which led me to believe it was a memory leak:
[100023.123] Out of memory: kill process 9568 (update.pl) score 325406 or a child
[100023.123] Killed Process 9568 (update.pl)
I don't believe it is an issue with cron because of the stalling (for ~15 sec, sometimes) when running it via the command-line. Also, there are no environmental variables used (at least by what I've written, maybe underlying things do?)
Edit 2: I found the issue myself, with help from the below comment by mobrule (in response to this question). It turns out that the script was called from a crontab of a user (non-root) just once a day and that (non-root privs) caused a special infinite loop situation.
Sorry guys, I feel kinda stupid for not finding this before, but thanks.
mobrule, if you submit your comment as an answer, I will accept it as it lead to me finding the problem.
End Edits
Thanks,
Brian
P.S. I may be able to post small snippets of code, but not the whole thing due to company policy.
You could try using Devel::Size to profile some of your objects. e.g. in the main:: scope (the .pl file itself), do something like this:
use Devel::Size qw(total_size);
foreach my $varname (qw(varname1 varname2 ))
{
print "size used for variable $varname: " . total_size($$varname) . "\n";
}
Compare the actual size used to what you think is a reasonable value for each object. Something suspicious might pop out immediately (e.g. a cache that is massively bloated beyond anything that sounds reasonable).
Other things to try:
Eliminate bits of functionality one at a time to see if suddenly things get a lot better; I'd start with the use of any external libraries
Is the bad behaviour localized to just one particular machine, or one particular operating system? Move the program to other systems to see how its behaviour changes.
(In a separate installation) try upgrading to the latest Perl (5.10.1), and also upgrade all your CPAN modules
How do you know that it's a memory leak? I can think of many other reasons why the OS would kill a program.
The first question I would ask is "Does this program always work correctly from the command line?". If the answer is "No" then I'd fix these issues first.
On the other hand if the answer is "Yes", I would investigate all the differences between having the program executed under cron and from the command line to find out why it is misbehaving.
If it is run by cron, that shouldn't it die after iteration? If that is the case, hard for me to see how a memory leak would be a big deal...
Are you sure it is the script itself, and not the child processes that are using the memory? Perhaps it ends up creating a real lot of ssh sessions , instead of doing a bunch of stuff in one session?