Hi. Just a short message, confirming that after we've altered the tables to have matching types, deletes now take 1 ms, instead of 5 sec. Indexes are being used now.
Thanks for assistance. Regards Kristian ps. would be nice with some warnings or indications in analyze output when this happens. [cid:imagec5a681.PNG@530b3f9e.479048e5] Kristian Ejvind Linux System Administrator IT Operations | Technical Operations Resurs Bank Ekslingan 8 Box 222 09, SE-25467 Helsingborg Mobil: +46 728571483 Växel: +46 42 38 20 00 E-post: kristian.ejv...@resurs.se<mailto:kristian.ejv...@resurs.se> Webb: www.resursbank.se<http://www.resursbank.se> From: Maxim Boguk <maxim.bo...@gmail.com> Date: Wednesday, 24 July 2019 at 19:17 To: Kristian Ejvind <kristian.ejv...@resurs.se> Cc: "pgsql-performance@lists.postgresql.org" <pgsql-performance@lists.postgresql.org> Subject: Re: zabbix on postgresql - very slow delete of events On Wed, Jul 24, 2019 at 6:12 PM Kristian Ejvind <kristian.ejv...@resurs.se<mailto:kristian.ejv...@resurs.se>> wrote: Hi Maxim Thanks for your advice, and let me start with your second email, which I'll copy here: ===== Hi Kristian, After comparing structure of zabbix tables with same in my zabbix installation I found one very weird difference. Why type of events.eventid had been changed from default bigint to numeric? I suspect that the difference between events.eventid (numeric) type and event_recovery.*_eventid (bigint) types might lead to inability of use index during foreign key checks. Anyway it will be clearly visible on the pg_stat_xact_user_tables results (I now expect to see 3 sequential scan on event_recovery and may be on some other tables as well). Kind Regards, Maxim ===== Well spotted! On closer examination it seems that data types are wrong in several places. I suspect that this comes from the time when our Zabbix ran on a MySQL database, which was converted over to PostgreSQL a few years ago. I agree this discrepancy is suspicious and I will continue to examine it. Regarding your ideas in the email below, I can say that 1) is not valid, disk latency is in the range of a few ms. This is the output from your recommended query, which seems to verify your suspicions. zabbix_34=# begin; delete from zabbix.events where eventid = 7123123; select * from pg_stat_xact_user_tables where seq_scan>0 or idx_scan>0 order by seq_scan+idx_scan desc; rollback; Time: 0.113 ms Time: 4798.189 ms (00:04.798) relid | schemaname | relname | seq_scan | seq_tup_read | idx_scan | idx_tup_fetch | n_tup_ins | n_tup_upd | n_tup_del | n_tup_hot_upd --------+------------+----------------+----------+--------------+----------+---------------+-----------+-----------+-----------+--------------- 41940 | zabbix | event_recovery | 3 | 35495224 | 0 | 0 | 0 | 0 | 1 | 0 41675 | zabbix | alerts | 1 | 544966 | 1 | 0 | 0 | 0 | 0 | 0 42573 | zabbix | problem | 2 | 13896 | 0 | 0 | 0 | 0 | 0 | 0 41943 | zabbix | event_tag | 1 | 22004 | 0 | 0 | 0 | 0 | 0 | 0 41649 | zabbix | acknowledges | 1 | 47 | 0 | 0 | 0 | 0 | 0 | 0 41951 | zabbix | events | 0 | 0 | 1 | 1 | 0 | 0 | 1 | 0 260215 | zabbix | event_suppress | 1 | 0 | 0 | 0 | 0 | 0 | 0 | 0 Hi Kristian, This result definitely proves that indexes not used during foreign key checks (see that non-zero seq_scan counters for linked tables). Only possible reason (IMHO) that wrong usage numeric in place of bigint. I recommend change types of events.eventid (and any other similar fields) to bigint. It should resolve your performance issues with deletes on events table (as additional bonus - bigint a lot faster and compact type than numeric). -- Maxim Boguk Senior Postgresql DBA https://dataegret.com/<https://smex12-5-en-ctp.trendmicro.com:443/wis/clicktime/v1/query?url=https%3a%2f%2fdataegret.com&umid=90a98c9f-46cd-4941-b939-8da90b514311&auth=daed959355609b907128d19d56c675829c94a38e-92a73de4d891916aa17d6a4577153d5be0a70dd8> Phone RU: +7 985 433 0000 Phone UA: +380 99 143 0000 Phone AU: +61 45 218 5678 LinkedIn: http://www.linkedin.com/pub/maksym-boguk/80/b99/b1b Skype: maxim.boguk "??????, ?? ??? ?????????? ??? ?? ??????, ?? ?????? ??? ??-???????? ?????? ????? ? ??? ????? ??? ????"
