Shulou(Shulou.com)06/01 Report--

Modifying N bytes on the page can be regarded as a physical log. It includes the following types: MLOG_WRITE_STRING, MLOG_8BYTES, MLOG_2BYTES, MLOG_1BYTES, MLOG_4BYTES. All kinds of page list pointer modifications and file headers and segment page content changes are logged in these ways. The specific format is as follows:

1 、 MLOG_2BYTES 、 MLOG_1BYTES 、 MLOG_4BYTES:

2 、 MLOG_8BYTES

3 、 MLOG_WRITE_STRING

4. Variable length byte algorithm mach_write_compressed:

If (n < 0x80UL) {mach_write_to_1 (b, n); return (1);} else if (n < 0x4000UL) {mach_write_to_2 (b, n | 0x8000UL); return (2);} else if (n < 0x200000UL) {mach_write_to_3 (b, n | 0xC00000UL); return (3) } else if (n < 0x10000000UL) {mach_write_to_4 (b, n | 0xE0000000UL); return (4);} else {mach_write_to_1 (b, 0xF0UL); mach_write_to_4 (b + 1, n); return (5);}

5. Mlog_write_ulint, mlog_write_ull, and mlog_log_string are the log writing functions for writing 1, 2, and 4-byte strings, respectively.

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