čt 30. 1. 2020 v 10:44 odesílatel Konstantin Knizhnik < k.knizh...@postgrespro.ru> napsal:
> > > On 30.01.2020 12:23, Pavel Stehule wrote: > > > Building regular index requires two kinds of lock: >> 1. You have to lock pg_class to make changes in system catalog. >> 2. You need to lock heap relation to pervent concurrent updates while >> building index. >> >> GTT requires 1) but not 2). >> Once backend inserts information about new index in system catalog, all >> other sessions may use it. pg_class lock prevents any race condition here. >> And building index itself doesn't affect any other backends. >> > > It is true. The difference for GTT, so any other sessions have to build > index (in your proposal) as extra operation against original plan. > > What is "index"? > For most parts of Postgres it is just an entry in system catalog. > And only executor deals with its particular implementation and content. > > My point is that if we process GTT index metadata in the same way as > regular index metadata, > then there will be no differences for the postgres between GTT and regular > indexes. > And we can provide the same behavior. > There should be a difference - index on regular table is created by one process. Same thing is not possible on GTT. So there should be a difference every time. You can reduce some differences, but minimally me and Robert don't feel it well. Starting a building index from routine, that is used for reading from buffer doesn't look well. I can accept some stranges, but I need to have feeling so it is necessary. I don't think so it is necessary in this case. Regards Pavel > Concerning actual content of the index - it is local to the backend and it > is safe to construct it a t any point of time (on demand). > It depends only on private data and can not be somehow affected by other > backends (taken in account that we preserve locking policy of regular > tables). > > > -- > Konstantin Knizhnik > Postgres Professional: http://www.postgrespro.com > The Russian Postgres Company > >
