Commit c04c42ae authored by Martin Kraemer's avatar Martin Kraemer
Browse files

Add notice about some inefficient SVR4 implementations of time zones in gettimeofday() 


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk@80925 13f79535-47bb-0310-9956-ffa450edef68
parent ce9e244d

docs/manual/platform/perf.html

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@@ -30,6 +30,7 @@ for the heavier TCP load, hardware/software conflicts that arise, etc. 
<LI><A HREF="#Linux">Linux</A>

<LI><A HREF="#Solaris">Solaris</A>

<LI><A HREF="#SunOS">SunOS 4.x</A>

<LI><A HREF="#SVR4">SVR4</A>

</UL>



<HR>
@@ -120,6 +121,54 @@ http://www.islandnet.com/~mark/somaxconn.html</A>. 


<P><HR>



<H3><A NAME="SVR4">

SVR4

</A></H3>



Some SVR4 versions waste three system calls on every

<SAMP>gettimeofday()</SAMP> call. Depending on the syntactic

form of the <SAMP>TZ</SAMP> environment variable, these

systems have several different algorithms to determine the

local time zone (presumably <EM>compatible</EM> with

something). The following example uses the central european

time zone to demonstrate this:

<DL>

 <DT><STRONG>TZ=:MET</STRONG>

 <DD>This form delegates the knowledge of the time zone

     information to an external compiled zoneinfo file

     (&agrave; la BSD).<BR>

     <STRONG>Caveat:</STRONG> Each time the gettimeofday()

     function is called, the external zone info is read in

     again (at least on some SVR4 systems). That results in

     three wasted system calls with every apache request

     served.<PRE>

     open("/usr/lib/locale/TZ/MET", O_RDONLY) = 3

     read(3, "\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0"..., 7944) = 778

     close(3)                                = 0</PRE>



 <DT><STRONG>TZ=MET-1MDT,M3.5.0/02:00:00,M10.5.0/03:00:00</STRONG>

 <DD>This syntax form (&agrave; la SYSV) contains all the

     knowledge about time zone beginning and ending times in

     its external representation. It has to be parsed each

     time it is evaluated, resulting in a slight computing

     overhead, but it requires no system call. Though the

     table lookup &agrave; la BSD is the more sophisticated

     technical solution, the bad SVR4 implementation makes

     this the preferred syntax on systems which otherwise

     access the external zone info file repeatedly.

</DL>

You should use the <SAMP>truss</SAMP> utility on a

single-process apache server (started with the <SAMP>-X</SAMP>

debugging switch) to determine whether your system can profit

from the second form of the <SAMP>TZ</SAMP> environment

variable. If it does, you could integrate the setting of the

preferred <SAMP>TZ</SAMP> syntax into the httpd startup

script, which is usually simply a copy of (or symbolic link

to) the <SAMP>apachectl</SAMP> utility script, or into the

system's <SAMP>/etc/TIMEZONE</SAMP> script.



<P><HR>



<H3>More welcome!</H3>



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