Every saga needs at least a second episode. |
What happens if data are not committed to a journaled file? To discover
the core of libjf
transactionality it's sufficient to remove
jf_file_commit statement as in
hello_world2.c example:
Example 2-2. hello_world2.c
1 #include <jf_file.h>
2 int main()
3 {
4 int rc;
5 jf_file_t jf;
6 size_t write;
7 rc = jf_file_open(&jf, NULL, "jf_tut_foo", "w", NULL);
8 if (JF_RC_OK != rc)
9 return 1;
10 rc = jf_file_printf(&jf, &write, "%s", "Hello world!\n");
11 if (JF_RC_OK != rc)
12 return 1;
13 rc = jf_file_close(&jf);
14 if (JF_RC_OK != rc)
15 return 1;
16 printf("Hello world II program is OK!\n");
17 return 0;
18 }
libtool --mode=link gcc -Wall -I/opt/libjf/include -L/opt/libjf/lib -ljf \
-o hello_world2 hello_world2.c
remove temporary files wrote by hello_world:
tiian@linux:~/tutorial> rm -f jf_tut_foo*
and run hello_world2 program:
tiian@linux:~/tutorial> ./hello_world2
Hello world II program is OK!
Take a look to files produced by hello_world2 execution:
tiian@linux:~/tutorial> ls -la jf_tut_foo*
-rw-r--r-- 1 tiian users 0 2005-08-11 11:05 jf_tut_foo
-rw-r--r-- 1 tiian users 8278 2005-08-11 11:05 jf_tut_foo.jf
jf_tut_foo is now an empty file because data was not
committed before calling jf_file_close (this
behavior is named "implicit rollback"); just for the sake of
curiosity, inspect the associated journal file:
tiian@linux:~/tutorial> jf_report -dt -j jf_tut_foo.jf
<?xml version="1.0" encoding="UTF-8"?>
<journal>
<header magic_number='0x41524153' version='1' file_id_mask='0x8'
file_id_mask_shift='3' size_mask='0xfffffff0' size_mask_shift='4'
file_size='4194304' file_num='3' rotation_threshold='0.800'
ctrl_recs='36' journal_recs='8278' />
<journaled_file_table max_files='2' number_of_files='2'
file_table='0x804b170'>
<file id='0' name='jf_tut_foo.jf' last_pos='8278' last_size='0'
status='0' last_uc_pos='0' last_uc_size='8278' stream='0x804b008' />
<file id='1' name='jf_tut_foo' last_pos='0' last_size='0' status='0'
last_uc_pos='0' last_uc_size='0' stream='(nil)' />
</journaled_file_table>
<records>
</records>
</journal>
no records have been written.