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Web Performance Tuning by Patrick Killelea

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Detailed Analysis of a Trace

Here is a system call trace of Apache 1.3 running on Linux. The runtime configuration file is essentially the default plus:

<Directory />
    AllowOverride none
    Options FollowSymLinks
</Directory>

The file being requested is a static 6K file of no particular content. Traces of non-static requests or requests with content negotiation look wildly different (and quite ugly in some cases). First we’ll look at the entire trace, then we’ll examine details. (This was generated by the strace program, other similar programs include truss, ktrace, and par):

accept(15, {sin_family=AF_INET, sin_port=htons(22283), sin_addr=inet_addr("127.0.0.1")}, [16]) = 3 flock(18, LOCK_UN) = 0 sigaction(SIGUSR1, {SIG_IGN}, {0x8059954, [], SA_INTERRUPT}) = 0 getsockname(3, {sin_family=AF_INET, sin_port=htons(8080), sin_addr=inet_addr("127.0.0.1")}, [16]) = 0 setsockopt(3, IPPROTO_TCP1, [1], 4) = 0 read(3, "GET /6k HTTP/1.0\r\nUser-Agent: "..., 4096) = 60 sigaction(SIGUSR1, {SIG_IGN}, {SIG_IGN}) = 0 time(NULL) = 873959960 gettimeofday({873959960, 404935}, NULL) = 0 stat("/home/dgaudet/ap/apachen/htdocs/6k", {st_mode=S_IFREG|0644, st_size=6144, ...}) = 0 open("/home/dgaudet/ap/apachen/htdocs/6k", O_RDONLY) = 4 mmap(0, 6144, PROT_READ, MAP_PRIVATE, 4, 0) = 0x400ee000 writev(3, [{"HTTP/1.1 200 OK\r\nDate: Thu, 11"..., 245}, {"\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0"..., 6144}], 2) = 6389 close(4) = 0 time(NULL) = 873959960 write(17, "127.0.0.1 - - [10/Sep/1997:23:39"..., 71) = 71 gettimeofday({873959960, ...

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