From: | "Hayato Kuroda (Fujitsu)" <kuroda(dot)hayato(at)fujitsu(dot)com> |
---|---|
To: | "Zhijie Hou (Fujitsu)" <houzj(dot)fnst(at)fujitsu(dot)com> |
Cc: | shveta malik <shveta(dot)malik(at)gmail(dot)com>, Nisha Moond <nisha(dot)moond412(at)gmail(dot)com>, pgsql-hackers <pgsql-hackers(at)postgresql(dot)org>, Dilip Kumar <dilipbalaut(at)gmail(dot)com>, Jan Wieck <jan(at)wi3ck(dot)info>, Ashutosh Bapat <ashutosh(dot)bapat(dot)oss(at)gmail(dot)com>, Amit Kapila <amit(dot)kapila16(at)gmail(dot)com> |
Subject: | RE: Conflict detection and logging in logical replication |
Date: | 2024-08-07 06:59:59 |
Message-ID: | TYAPR01MB5692C288CD6F14ED80531E48F5B82@TYAPR01MB5692.jpnprd01.prod.outlook.com |
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Lists: | pgsql-hackers |
Dear Hou,
While playing with the 0003 patch (the patch may not be ready), I found that
when the insert_exists event occurred, both apply_error_count and insert_exists_count
was counted.
```
-- insert a tuple on the subscriber
subscriber =# INSERT INTO tab VALUES (1);
-- insert the same tuple on the publisher, which causes insert_exists conflict
publisher =# INSERT INTO tab VALUES (1);
-- after some time...
subscriber =# SELECT * FROM pg_stat_subscription_stats;
-[ RECORD 1 ]--------+------
subid | 16389
subname | sub
apply_error_count | 16
sync_error_count | 0
insert_exists_count | 16
update_differ_count | 0
update_exists_count | 0
update_missing_count | 0
delete_differ_count | 0
delete_missing_count | 0
stats_reset |
```
Not tested, but I think this could also happen for the update_exists_count case,
or sync_error_count may be counted when the tablesync worker detects the conflict.
IIUC, the reason is that pgstat_report_subscription_error() is called in the
PG_CATCH part in start_apply() even after ReportApplyConflict(ERROR) is called.
What do you think of the current behavior? I wouldn't say I like that the same
phenomenon is counted as several events. E.g., in the case of vacuum, the entry
seemed to be separated based on the process by backends or autovacuum.
I feel the spec is unfamiliar in that only insert_exists and update_exists are
counted duplicated with the apply_error_count.
An easy fix is to introduce a global variable which is turned on when the conflict
is found.
Thought?
Best regards,
Hayato Kuroda
FUJITSU LIMITED
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