Re: Timing out A Blocker Based on Time or Count of Waiters
От | Adrian Klaver |
---|---|
Тема | Re: Timing out A Blocker Based on Time or Count of Waiters |
Дата | |
Msg-id | 8a8aef5b-5239-4617-8b4c-ec54de02d4bb@aklaver.com обсуждение исходный текст |
Ответ на | Re: Timing out A Blocker Based on Time or Count of Waiters (Fred Habash <fmhabash@gmail.com>) |
Список | pgsql-general |
On 3/22/24 12:41, Fred Habash wrote: > Lock tree: All PID's waiting on a lock held by/blocked by single blocker > PID. Similar to what you see in the output of this script: > https://github.com/dataegret/pg-utils/blob/master/sql/locktree.sql > <https://github.com/dataegret/pg-utils/blob/master/sql/locktree.sql> . > It uses the dot connotation to draw a tree. > > Waiters: The PID (first column) returned by this query, for example > > SELECT > activity.pid, > activity.usename, > activity.query, > blocking.pid AS blocking_id, > blocking.query AS blocking_query > FROM pg_stat_activity AS activity > JOIN pg_stat_activity AS blocking ON blocking.pid = > ANY(pg_blocking_pids(activity.pid)); > > DDL example: An 'alter table ... alter column ...' would cause all DML > and SELECT statements to wait/block. > > Hope this answers your question. Thanks for your interest. Yes. To me the issue is, "Facing an issue where sometimes humans login to a database and run DDL statements causing a long locking tree of over 1000 waiters." where the problem is people running disruptive statements without regard to planning or what else is happening on the database. I am not sure that dropping a statement just based on a count is progress. If the DDL is important then it needs to be run at some point and you are conceivably back at the same blocking issue. This then leads to two possibilities either the DDL is not important and shouldn't be run or it is and some thought and timing needs to be applied before it is run. > > On Fri, Mar 22, 2024 at 12:32 PM Adrian Klaver > <adrian.klaver@aklaver.com <mailto:adrian.klaver@aklaver.com>> wrote: > > On 3/22/24 09:25, Fred Habash wrote: > > Facing an issue where sometimes humans login to a database and > run DDL > > statements causing a long locking tree of over 1000 waiters. As a > > The above needs more explanation: > > 1) Define locking tree. > > 2) Define waiters. > > 3) Provide examples of the DDL. > > > > workaround, we asked developers to always start their DDL sessions > > with 'SET lock_timeout = 'Xs'. > > > > I reviewed the native lock timeout parameter in Postgres and > found 7. > > None seem to be related to blocker timeouts directly. > > > > idle_in_transaction_session_timeout > > idle_session_timeout > > lock_timeout: How long a session waits for a lock > > statement_timeout > > authentication_timeout > > deadlock_timeout > > log_lock_waits > > > > Instead, I put together a quick procedure that counts waiter > sessions > > for a given blocker and terminates it if waiter count exceeds a > threshold. > > > > Is there not a native way to ... > > 1. Automatically time out a blocker > > 2. A metric that shows how many waiters for a blocker? > > > > Thanks > > -- > > > > ---------------------------------------- > > Thank you > > > > > > -- > Adrian Klaver > adrian.klaver@aklaver.com <mailto:adrian.klaver@aklaver.com> > > > > -- > > ---------------------------------------- > Thank you > > -- Adrian Klaver adrian.klaver@aklaver.com
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