---- On Thu, 24 Nov 2022 08:00:59 -0700 Thomas Kellerer wrote --- > Pavel Stehule schrieb am 24.11.2022 um 07:03: > > There are many Oracle users that find global indexes useful despite > > their disadvantages. > > > > I have seen this mostly when the goal was to get the benefits of > > partition pruning at runtime which turned the full table scan (=Seq > > Scan) > > on huge tables to partition scans on much smaller partitions. > > Partition wise joins were also helpful for query performance. > > The substantially slower drop partition performance was accepted in > > thos cases > > > > > > I think it would be nice to have the option in Postgres as well. > > > > I do agree however, that the global index should not be created > > automatically. > > > > Something like CREATE GLOBAL [UNIQUE] INDEX ... would be a lot better > > > > > > Is it necessary to use special marks like GLOBAL if this index will > > be partitioned, and uniqueness will be ensured by repeated > > evaluations? > > > > Or you think so there should be really forced one relation based > > index? > > > > I can imagine a unique index on partitions without a special mark, > > that will be partitioned, and a second variant classic index created > > over a partitioned table, that will be marked as GLOBAL. > > > My personal opinion is, that a global index should never be created > automatically. > > The user should consciously decide on using a feature > that might have a serious impact on performance in some areas.
Agreed, if a unique index is created on non-partition key columns without including the special mark (partition key columns), it may be a mistake from user. (At least I make this mistake all the time). Current PG will give you a warning to include the partition keys, which is good. If we were to automatically turn that into a global unique index, user may be using the feature without knowing and experiencing some performance impacts (to account for extra uniqueness check in all partitions).
