On this page:
http://httpd.apache.org/docs/2.2/mod/mod_unique_id.html
it says, "The UNIQUE_ID environment variable is constructed by encoding
the 112-bit (32-bit IP address, 32 bit pid, 32 bit time stamp, 16 bit
counter) quadruple using the alphabet [EMAIL PROTECTED] in a manner similar
to MIME base64 encoding, producing 19 characters."
However, in the log files of my new server, the Unique ID is always 24
characters. Am I missing something?
I enabled mod_unique_id and put it in my LogFormat like this
"%{UNIQUE_ID}e". I have Apache 2.2.3 on FreeBSD 6.0. The length is not
causing me any problems, I just want to know if something was changed.
I think I figured it out.
In 2.2.3 mod_unique_id.c, the unique_id structure is defined as:
typedef struct {
unsigned int stamp;
unsigned int in_addr;
unsigned int pid;
unsigned short counter;
unsigned int thread_index;
} unique_id_rec;
In 1.3.36 mod_unique_id.c, the unique_id structure is defined as:
typedef struct {
unsigned int stamp;
unsigned int in_addr;
unsigned int pid;
#ifdef MULTITHREAD
unsigned int tid;
#endif
unsigned short counter;
} unique_id_rec;
My old Apache version did not have MULTITHREAD defined in the build
options (found by running httpd -V). In Apache 2.0+, multi-threading is
enabled by default. Thus, the old structure is 112 bits (divide by 6 to
get psuedo-UUencoded base64 value), or 19 characters. The new structure
(or the old one with multi-threading) is 144 bits, which translates to
24 characters. Therefore, in all 2.0+ versions of Apache on typical
32-bit systems, the UniqueID will be 24 characters. However, it will
still vary based on the size of integral types on the host system.
I want to eventually store the UniqueID in a MySQL Archive table. It
helps to know the fixed size for the the field in the table.
Maybe this can be made more clear in the documentation?
Sincerely,
Shailesh
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