| Bug #109829 | Bug of function minAck in semisync plugin lead to unexpected behavior | ||
|---|---|---|---|
| Submitted: | 29 Jan 2023 9:52 | Modified: | 30 Jan 2023 14:46 |
| Reporter: | Ken Lau (OCA) | Email Updates: | |
| Status: | Verified | Impact on me: | |
| Category: | MySQL Server: Replication | Severity: | S3 (Non-critical) |
| Version: | all | OS: | Any |
| Assigned to: | CPU Architecture: | Any | |
| Tags: | semi-sync | ||
[30 Jan 2023 14:46]
MySQL Verification Team
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Description: There is a bug in function minAck in semisync_source.h in semisync plugin. The function doesn't find the minimum ack but the maximum index ack which is smaller than given position. And this will lead to unexpected behavior when rpl_semi_sync_master_wait_slaves is set to more than 3. ``` /** Find the minimum ack which is smaller than given position. When more than one slots are minimum acks, it returns the one has smallest index. @param[in] log_file_name binlog file name @param[in] log_file_pos binlog file position @return NULL if no ack is smaller than given position, otherwise return its pointer. */ AckInfo *minAck(const char *log_file_name, my_off_t log_file_pos) { unsigned int i; AckInfo *ackinfo = nullptr; for (i = 0; i < m_size; i++) { if (m_ack_array[i].less_than(log_file_name, log_file_pos)) ackinfo = m_ack_array + i; } return ackinfo; } ``` How to repeat: Suppose rpl_semi_sync_master_wait_slaves = 4. coming acks slot 1 slot 2 slot 3 =========== ========== ========== ========== 1:log1:120 1:log1:120 2:log1:120 1:log1:120 2:log1:120 1:log1:150 1:log1:150 2:log1:120 1:log1:170 1:log1:170 2:log1:120 3:log1:150 1:log1:170 2:log1:120 3:log1:150 4:log1:170 The minAck will return '3:log1:150' and m_greatest_ack will asign to '3:log1:150' too. Then the array will look like: coming acks slot 1 slot 2 slot 3 =========== ========== ========== ========== 1:log1:170 2:log1:120 log1:170 Slot 2 in this case will never become empty again. Suggested fix: Just fix the bug in minAck. Like: ``` AckInfo *minAck(const char *log_file_name, my_off_t log_file_pos) { unsigned int i; AckInfo *ackinfo = nullptr; const char *min_log_file_name = log_file_name; my_off_t min_log_file_pos = log_file_pos; for (i = 0; i < m_size; i++) { if (m_ack_array[i].less_than(min_log_file_name, min_log_file_pos)) { ackinfo = m_ack_array + i; min_log_file_name = m_ack_array[i].binlog_name; min_log_file_pos = m_ack_array[i].binlog_pos; } } ``` return ackinfo; }