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Hi, I have a couple of questions about the inner workings
of the apachectl graceful command and I can’t seem to find the answer
anywhere so maybe you can help. Normally with a graceful the following happens. I issue a graceful. With strace I see something like this: stat64("/usr/local/apache/conf/sites/www.blah.com",
{st_mode=S_IFREG|0644, st_size=680, ...}) = 0 open("/usr/local/apache/conf/sites/www.blah.com",
O_RDONLY) = 4 fstat64(4,
{st_mode=S_IFREG|0644, st_size=680, ...}) = 0 read(4, "ServerRoot
/usr/local/apache\n###"..., 4096) = 680 stat64("/usr/local/apache",
{st_mode=S_IFDIR|S_ISGID|0755, st_size=4096, ...}) = 0 read(4, "",
4096)
= 0 etc.etc. Then I see this: stat64("/usr/home/ws/blah/www.blah.com/www/",
{st_mode=S_IFDIR|0755, st_size=4096, ...}) = 0 etc.etc. So my config is read and the DocumentRoots from the
VHost are ‘statted’ on the disc. This process/pid is done rather quickly after which I
see that this process terminates. During this time Apache functions fine! Next I can see with strace that the main Apache
thread is “taking over”. So in this case 25527. 25527
? Ss 10:01
/usr/local/apache/bin/httpd -k start 5371
? S
0:15 \_ /usr/local/apache/bin/httpd -k start According to strace this happens: stat64("/usr/home/ws/blah/www.blah.nl/www/",
{st_mode=S_IFDIR|0755, st_size=4096, ...}) = 0 etc.etc. Apache is “statting” all the DocumentRoot
directories on disk. This usually takes a long time and at this point
Apache stops accepting new threads! This is really painful. My question based on my observations are: I did a little research on the stat64 function and
this seems to be a function that causes a lot of IO. From what I gather all
extended file attributes for all dirs are processed. This seems like of lot of
attributes. 1. It seems Apache does an stat64 of my DocumentRoots
twice! Why? This doesn’t make sense. First with the graceful command and
next the Apache process itself. 2. Is there a way to get rid of stat64 or use a
lighter/less intense stat function? 3. Further it seems when Apache is actually
restarting/gracefulling that Apache stops accepting new threads. This isn’t
very convenient. What can I do about this? I run my Apache server from a NFS storage mount. Statting
files by querying their (extended) attributes is very costly/slow/inefficient. So
I’m running into problems; are there ways to speed this up (apart from
the obvious NFS and other filesystem optimizations I have done). I seems Apache is statting the directories because it
wants to make sure it exists. But should I care whether a DocumentRoot from a
Virtual Host exists? I’ve tested deleting directories and this doesn’t
crash Apache. So what’s the reason behind this. Hope someone can provide some insight. Cheers. Jan van den Berg |
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