| Bug #115351 | page tracking cannot find stop point | ||
|---|---|---|---|
| Submitted: | 17 Jun 4:32 | Modified: | 17 Jun 11:42 |
| Reporter: | gang liu | Email Updates: | |
| Status: | Can't repeat | Impact on me: | |
| Category: | MySQL Server: InnoDB storage engine | Severity: | S3 (Non-critical) |
| Version: | mysql-8.0.32 | OS: | Any |
| Assigned to: | CPU Architecture: | Any | |
| Tags: | page-tracking | ||
[17 Jun 9:32]
MySQL Verification Team
Hi Mr. liu, Thank you for your bug report. However, we do not see why this should be a bug ??? In the latest software releases, struct Arch_Page_Pos has that variable defined properly: uint64_t m_block_num; Hence, we do not see why would we require a cast in that place ???? Not a bug
[17 Jun 10:10]
gang liu
if binary search stop condition is right_pos.m_block_num = -1, it will be 18446744073709551615. since, right_pos.m_block_num is uint64_t. then, the binary search will not stop.
[17 Jun 10:24]
MySQL Verification Team
Hi Mr. liu, Can you point us to the code where that assignment: right_pos.m_block_num = -1 is made ????
[17 Jun 10:27]
gang liu
` if middle_pos.m_block_num=0, `right_pos.m_block_num = middle_pos.m_block_num - 1;
[17 Jun 10:34]
MySQL Verification Team
Hi, Can you, please, name the source file and the line number in 8.0.37 ???
[17 Jun 11:00]
gang liu
mysql-8.0.37, storage/innobase/arch/arch0page.cc:559
[17 Jun 11:09]
MySQL Verification Team
Hi Mr. Liu,
We see this code around that line number:
if (block_stop_lsn > check_lsn) {
right_pos.m_block_num = middle_pos.m_block_num - 1;
} else {
left_pos.m_block_num = middle_pos.m_block_num + 1;
}
right_pos.m_block_num is NOT assigned to -1.
It can be -1 only if middle_pos.m_block_num is 0, which can nothappen at all.
[17 Jun 11:42]
gang liu
```
...
while (left_pos.m_block_num <= right_pos.m_block_num) {
middle_pos.m_block_num = left_pos.m_block_num +
(right_pos.m_block_num - left_pos.m_block_num) / 2;
....
if (block_stop_lsn > check_lsn) {
right_pos.m_block_num = middle_pos.m_block_num - 1;
} else {
left_pos.m_block_num = middle_pos.m_block_num + 1;
}
}
...
```
assum initial condition： left_pos.m_block_num = 0, right_pos.m_block_num =12
1th loop：
middle_pos.m_block_num = 6，left_pos.m_block_num = 0, right_pos.m_block_num =5
2th loop：
middle_pos.m_block_num = 2，left_pos.m_block_num = 0, right_pos.m_block_num =1
3th loop：
middle_pos.m_block_num = 0，left_pos.m_block_num = 0, right_pos.m_block_num =-1
[17 Jun 14:25]
MySQL Verification Team
Hi, We are afraid that this scenario is not possible, but we shall check it out again ......
[17 Jun 14:26]
MySQL Verification Team
Hi, Even if it is a possible scenario, a patch would be different ....... to prevent the subtraction when the left operand is 0 (zero).
Description: in function: ``` bool Arch_File_Ctx::find_stop_point(Arch_Group *group, lsn_t check_lsn, Arch_Point &stop_point, Arch_Page_Pos last_pos){ ... while (left_pos.m_block_num <= right_pos.m_block_num) { middle_pos.m_block_num = left_pos.m_block_num + (right_pos.m_block_num - left_pos.m_block_num) / 2; .... if (block_stop_lsn > check_lsn) { right_pos.m_block_num = middle_pos.m_block_num - 1; } else { left_pos.m_block_num = middle_pos.m_block_num + 1; } } ... ``` there is one condition is: left_pos.m_block_num = 0, right_pos.m_block_num =-1, ince the the type of right_pos.m_block_num is int64_t, then the condition (left_pos.m_block_num < right_pos.m_block_num) is right, // the group will open a file which not exist. How to repeat: see the description. Suggested fix: diff --git a/storage/innobase/arch/arch0page.cc b/storage/innobase/arch/arch0page.cc index bc07f88c78c..946eefef2b6 100644 --- a/storage/innobase/arch/arch0page.cc +++ b/storage/innobase/arch/arch0page.cc @@ -524,7 +524,8 @@ bool Arch_File_Ctx::find_stop_point(Arch_Group *group, lsn_t check_lsn, lsn_t block_stop_lsn; int err; - while (left_pos.m_block_num <= right_pos.m_block_num) { + while (static_cast<int64_t>(left_pos.m_block_num) <= + static_cast<int64_t>(right_pos.m_block_num)) { Arch_Page_Pos middle_pos; middle_pos.init(); middle_pos.m_offset = 0;