On Mon, Jun 28, 2021 at 9:50 AM Amit Langote <amitlangot...@gmail.com> wrote: > > On Thu, Jun 24, 2021 at 7:27 AM David Rowley <dgrowle...@gmail.com> wrote: > > On Wed, 23 Jun 2021 at 21:07, Amit Kapila <amit.kapil...@gmail.com> wrote: > > > I noticed that while inserting directly into a partition table we > > > compute the PartitionCheckExpr by traversing all the parent partitions > > > via > > > ExecPartitionCheck()->RelationGetPartitionQual()->generate_partition_qual(). > > > We take AccessShareLock on parent tables while generating qual. > > > > > > Now, on the other hand, while dropping constraint on a partitioned > > > table, we take the lock from parent to all the child tables. > > > > > > I think taking locks in opposite directions can lead to deadlock in > > > these operations. > > > > I wonder if it's possible to do any better here? Surely when > > traversing from child to parent we must lock the child before checking > > what the parent relation is. > > I remember there was a discussion where I proposed to document the > deadlock hazard that exists when performing DML directly on > partitions. >
+1. I think it is better if we can also write in code comments or README about this. How about adding something to README/code about locking of partitions for different operations? Unless I am missing it, I think some of this information is there in bits and pieces but it would be great if we can have it consolidated at someplace. > The proposal didn't get enough attention, perhaps because > it was in the middle of a long reply about other concerns: > > https://www.postgresql.org/message-id/16db1458-67cf-4add-736e-31b053115e8e%40lab.ntt.co.jp > > Maybe a good idea to add a line or 2 in 5.11. Table Partitioning? > Sounds reasonable, but I think it would be better if can mention the scenarios/cases where there is a possibility of deadlocks. -- With Regards, Amit Kapila.
